Historical Background Calreticulin was discovered in the early 1970s as a high affinity calcium-b... more Historical Background Calreticulin was discovered in the early 1970s as a high affinity calcium-binding protein (HACBP) of the sarcoplasmic reticulum (Ostwald and Mac-Lennan 1974). Later, based on N-terminal amino acid sequence analysis and molecular cloning of cDNA encoding calreticulin, it was realized that the protein was identical to calregulin, CRP55, CaBP3, ERp60, and calsequestrin-like protein (Michalak et al. 2009). The name "calreticulin" is now universally accepted to reflect the protein's Ca 2+ binding capacity and localization in the sarcoplasmic/endoplasmic reticulum (ER). Calreticulin is a ubiquitous protein that is present in all eukaryotic cells except for erythrocytes, as these cells lack ER. There is reduced abundance
Current evidence supports a protective role for virus neutralizing antibodies in immunity against... more Current evidence supports a protective role for virus neutralizing antibodies in immunity against HCV infection. Many cross-neutralizing monoclonal antibodies have been identified. These antibodies have been shown to protect or clear infection in animal models. Previous clinical trials have shown a gpE1/gpE2 vaccine can induce antibodies that neutralize theinfectivity of all the major HCVcc genotypes around the world. However, cross-neutralization appeared to favour certain genotypes with significant but lower neutralization against others. HCV may employ epitope masking to avoid antibody-mediated neutralization. The hypervariable region-1 (HVR1) at the amino-terminus of glycoprotein E2 has been shown to restrict access to many neutralizing antibodies. Consistent with this, other groups have reported that recombinant viruses lacking the HVR1 are hypersensitive to neutralization. It has been proposed that gpE1/gpE2 lacking this domain could be a better vaccine antigen to induce broad...
In multiple sclerosis (MS), a demyelinating inflammatory disease of the CNS, and its animal model... more In multiple sclerosis (MS), a demyelinating inflammatory disease of the CNS, and its animal model (experimental autoimmune encephalomyelitis; EAE), circulating immune cells gain access to the CNS across the blood-brain barrier to cause inflammation, myelin destruction, and neuronal damage. Here, we discovered that calnexin, an ER chaperone, is highly abundant in human brain endothelial cells of MS patients. Conversely, mice lacking calnexin exhibited resistance to EAE induction, no evidence of immune cell infiltration into the CNS, and no induction of inflammation markers within the CNS. Furthermore, calnexin deficiency in mice did not alter the development or function of the immune system. Instead, the loss of calnexin led to a defect in brain endothelial cell function that resulted in reduced T cell trafficking across the blood-brain barrier. These findings identify calnexin in brain endothelial cells as a potentially novel target for developing strategies aimed at managing or pre...
Calreticulin is an endoplasmic reticulum (ER) resident protein critical for maintaining Ca(2+) ho... more Calreticulin is an endoplasmic reticulum (ER) resident protein critical for maintaining Ca(2+) homeostasis and glycoprotein folding in the ER. The protein has also been identified on the cell surface of apoptotic and necrotic cells and implicated to play a role in immunogenic cell death and other extracellular functions. The molecular events that promote cell surface association of calreticulin are not clear. Under cell stress conditions (environmental, drug induced, hypoxia), calreticulin may be upregulated as it attempts to regulate cell survival, death or repair. The initial signaling mechanisms involved in these processes may be regulated by the unfolded protein response (UPR) and genome damage response (GDR) pathways. Area covered: Here, the phenomenon of cell surface calreticulin and its extracellular functions are discussed, with a major emphasis on the process of immunogenic cell death. The evidence of how cell surface calreticulin may act as a damage associated molecular pattern molecule is evaluated, in addition to how these properties of the protein can be exploited for therapeutic vaccine development, cancer treatment and mediating other inflammatory processes. In addition, clarification of calreticulin functions from its intracellular, cell surface, and extracellular locations are provided. Expert opinion: While the protein folding and immune-stimulatory properties of calreticulin can be exploited to develop therapies, the molecular pathways involved remain to be elucidated. Nevertheless, exploiting the multifaceted properties of calreticulin may in the future provide a means to treat a number of diseases.
The disruption of the energy or nutrient balance triggers endoplasmic reticulum (ER) stress, a pr... more The disruption of the energy or nutrient balance triggers endoplasmic reticulum (ER) stress, a process that mobilizes various strategies, collectively called the unfolded protein response (UPR), which reestablish homeostasis of the ER and cell. Activation of the UPR stress sensor IRE1α (inositol-requiring enzyme 1α) stimulates its endoribonuclease activity, leading to the generation of the mRNA encoding the transcription factor XBP1 (X-box binding protein 1), which regulates the transcription of genes encoding factors involved in controlling the quality and folding of proteins. We found that the activity of IRE1α was regulated by the ER oxidoreductase PDIA6 (protein disulfide isomerase A6) and the microRNA miR-322 in response to disruption of ER Ca2+ homeostasis. PDIA6 interacted with IRE1α and enhanced IRE1α activity as monitored by phosphorylation of IRE1α and XBP1 mRNA splicing, but PDIA6 did not substantially affect the activity of other pathways that mediate responses to ER str...
Biochimica et Biophysica Acta (BBA) - Molecular Cell Research, 2014
Myelin oligodendrocyte glycoprotein (MOG) is a type I integral membrane protein that is expressed... more Myelin oligodendrocyte glycoprotein (MOG) is a type I integral membrane protein that is expressed in the central nervous system. MOG has a single N-glycosylation site within its extracellular domain. MOG has been linked with pathogenesis of multiple sclerosis; anti-MOG antibodies have been detected in the sera of multiple sclerosis patients. N-glycosylation is an important post-translational modification of protein that might impact their folding, localization and function. However, the role of sugar in the biology of MOG is not well understood. In this study, we created a mutant MOG lacking N-linked glycan and tested its properties. We concluded that the lack of sugar did not impact on MOG abundance in the absence of endoplasmic reticulum molecular chaperone calnexin. We also show that the absence of N-glycan did not interfere with MOG's subcellular localization and it did not result in activation of endoplasmic reticulum stress. This article is part of a Special Issue entitled: 13th European Symposium on Calcium.
Canadian Journal of Physiology and Pharmacology, 2012
The endoplasmic reticulum has an intricate network of pathways built to deal with the secretory a... more The endoplasmic reticulum has an intricate network of pathways built to deal with the secretory and integral membrane protein synthesis demands of the cell, as well as adaptive responses set up for the endoplasmic reticulum to rely on when stressed. These pathways are both essential and complex, and because of these 2 factors, several situations can lead to a dysfunctional endoplasmic reticulum and result in a dysfunctional cell with the potential to contribute to the progression of disease. The endoplasmic reticulum has been implicated in several metabolic, neurodegenerative, inflammatory, autoimmune, and renal diseases and disorders, and in particular, cardiovascular diseases. The role of the endoplasmic reticulum in cardiovascular disease shows how the change in function of a particular microscopic organelle can lead to macroscopic changes in the form of disease.
Biochemical and Biophysical Research Communications, 2012
Our previous studies have demonstrated that prion protein (PrP) leads to disassembly of microtubu... more Our previous studies have demonstrated that prion protein (PrP) leads to disassembly of microtubular cytoskeleton through binding to tubulin and its oligomerization. Here we found that PrP-treated cells exhibited improper morphology of mitotic spindles. Formation of aberrant spindles may result not only from altered microtubule dynamics - as expected from PrP-induced tubulin oligomerization - but also from impairing the function of molecular motors. Therefore we checked whether binding of PrP to microtubules affected movement generated by Ncd - a kinesin responsible for the proper organization of division spindles. We found that PrP inhibited Ncd-driven transport of microtubules. Most probably, the inhibition of the microtubule movement resulted from PrP-induced changes in the microtubule structure since Ncd-microtubule binding was reduced already at low PrP to tubulin molar ratios. This study suggests another plausible mechanism of PrP cytotoxicity related to the interaction with tubulin, namely impeding microtubule-dependent transport.
Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease, 2012
Missense mutations in human TPM3 gene encoding γ-tropomyosin expressed in slow muscle type 1 fibe... more Missense mutations in human TPM3 gene encoding γ-tropomyosin expressed in slow muscle type 1 fibers, were associated with three types of congenital myopathies-nemaline myopathy, cap disease and congenital fiber type disproportion. Functional effects of the following substitutions: Leu100Met, Ala156Thr, Arg168His, Arg168Cys, Arg168Gly, Lys169Glu, and Arg245Gly, were examined in biochemical assays using recombinant tropomyosin mutants and native proteins isolated from skeletal muscle. Most, but not all, mutations decreased the affinity of tropomyosin for actin alone and in complex with troponin (±Ca(2+)). All studied tropomyosin mutants reduced Ca-induced activation but had no effect on the inhibition of actomyosin cross-bridges. Ca(2+)-sensitivity of the actomyosin interactions, as well as cooperativity of myosin-induced activation of the thin filament was affected by individual tropomyosin mutants with various degrees. Decreased motility of the reconstructed thin filaments was a result of combined functional defects caused by myopathy-related tropomyosin mutants. We conclude that muscle weakness and structural abnormalities observed in TPM3-related congenital myopathies result from reduced capability of the thin filament to fully activate actin-myosin cross-bridges.
Kinesins form a large and diverse superfamily of proteins involved in numerous important cellular... more Kinesins form a large and diverse superfamily of proteins involved in numerous important cellular processes. The majority of them are molecular motors moving along microtubules. Conversion of chemical energy into mechanical work is accomplished in a sequence of events involving both biochemical and conformational alternation of the motor structure called the mechanochemical cycle. Different members of the kinesin superfamily can either perform their function in large groups or act as single molecules. Conventional kinesin, a member of the kinesin-1 subfamily, exemplifies the second type of motor which requires tight coordination of the mechanochemical cycle in two identical subunits to accomplish processive movement toward the microtubule plus end. Recent results strongly support an asymmetric handover hand model of ''walking'' for this protein. Conformational strain between two subunits at the stage of the cycle where both heads are attached to the microtubule seems to be a major factor in intersubunit coordination, although molecular and kinetic details of this phenomenon are not yet deciphered. We discuss also current knowledge concerning intersubunit coordination in other kinesin subfamilies. Members of the kinesin-3 class use at least three different mechanisms of movement and can translocate in monomeric or dimeric forms. It is not known to what extent intersubunit coordination takes place in Ncd, a dimeric member of the kinesin-14 subfamily which, unlike conventional kinesin, exercises a power-stroke toward the microtubule minus end. Eg5, a member of the kinesin-5 subfamily is a homotetrameric protein with two kinesin-1-like dimeric halves controlled by their relative orientation on two microtubules. It seems that diversity of subunit organization, quaternary structures and cellular functions in the kinesin superfamily are reflected also by the divergent extent and mechanism of intersubunit coordination during kinesin movement along microtubules.
A novel 120 kDa actin-binding protein (ApABP-F1) was found in Amoeba proteus. It was distributed ... more A novel 120 kDa actin-binding protein (ApABP-F1) was found in Amoeba proteus. It was distributed throughout the cytoplasm, mainly in the subplasma membrane and perinuclear–nuclear areas, enriched in actin. The full-length cDNA of ApABP consisted of 2672 nucleotides with an open reading frame of 878 amino acids, giving a *95 kDa protein with a theoretical pI value of 5.11. It had a novel domain organization pattern: the N terminus (residues 1–104) contained 1 calponin-homology (CH) domain, followed by only 1 region that was homologous to the filamin repeat (FR, residues 209–324), and a central region (residues 344–577) exhibiting a very high probability of coiled-coil formation, probably engaged in the observed protein dimerization. A phylogenetic tree constructed for CH domains from 25 various proteins revealed that the CH domain of ApABP was most related to that of the hypothetical mouse KIAA0903-like protein , whereas not much relationship to either filamins or the gelation factor (ABP-120) of Dictyostelium discoideum and Entamoeba histolytica was found. Résumé : Une nouvelle protéine de 120 kDa liant l'actine (ApABP) a e ´té identifiée chez Amoeba proteus. Elle e ´tait distri-buée a ` travers tout le cytoplasme, particulièrement dans la région sous la membrane plasmique ainsi que dans les régions périnucléaire et nucléaire enrichies en actine. L'ADNc de pleine longueur de ApABP comprenait 2672 nucléotides et un cadre de lecture ouvert de 878 acides aminés, résultant en une protéine d'environ 95 kDa dont le pI théorique e ´tait de 5.11. Ses domaines e ´taient organisés selon un nouveau patron : l'extrémité N terminale (résidus 1–104) contenait un do-maine homologue a ` la calponine (CH), suivi par une seule région homologue aux répétitions de filamine (FR, résidus 209-324), et une région centrale (résidus 344–577) formant probablement un domaine «coiled-coil», potentiellement impliqué dans la dimérisation observée de la protéine. L'arbre phylogénique des domaines CH construit a ` partir de 25 protéines a révélé que le domaine CH de ApABP e ´tait le plus apparenté au domaine CH d'une protéine hypothétique ressemblant a ` KIAA0903 chez la souris, alors que peu de relation avec les filamines ou avec les facteurs de gélification ABP-120 de Dictyostelium discoideum et d'Entamoeba histolytica n'e ´tait trouvée.
Historical Background Calreticulin was discovered in the early 1970s as a high affinity calcium-b... more Historical Background Calreticulin was discovered in the early 1970s as a high affinity calcium-binding protein (HACBP) of the sarcoplasmic reticulum (Ostwald and Mac-Lennan 1974). Later, based on N-terminal amino acid sequence analysis and molecular cloning of cDNA encoding calreticulin, it was realized that the protein was identical to calregulin, CRP55, CaBP3, ERp60, and calsequestrin-like protein (Michalak et al. 2009). The name "calreticulin" is now universally accepted to reflect the protein's Ca 2+ binding capacity and localization in the sarcoplasmic/endoplasmic reticulum (ER). Calreticulin is a ubiquitous protein that is present in all eukaryotic cells except for erythrocytes, as these cells lack ER. There is reduced abundance
Current evidence supports a protective role for virus neutralizing antibodies in immunity against... more Current evidence supports a protective role for virus neutralizing antibodies in immunity against HCV infection. Many cross-neutralizing monoclonal antibodies have been identified. These antibodies have been shown to protect or clear infection in animal models. Previous clinical trials have shown a gpE1/gpE2 vaccine can induce antibodies that neutralize theinfectivity of all the major HCVcc genotypes around the world. However, cross-neutralization appeared to favour certain genotypes with significant but lower neutralization against others. HCV may employ epitope masking to avoid antibody-mediated neutralization. The hypervariable region-1 (HVR1) at the amino-terminus of glycoprotein E2 has been shown to restrict access to many neutralizing antibodies. Consistent with this, other groups have reported that recombinant viruses lacking the HVR1 are hypersensitive to neutralization. It has been proposed that gpE1/gpE2 lacking this domain could be a better vaccine antigen to induce broad...
In multiple sclerosis (MS), a demyelinating inflammatory disease of the CNS, and its animal model... more In multiple sclerosis (MS), a demyelinating inflammatory disease of the CNS, and its animal model (experimental autoimmune encephalomyelitis; EAE), circulating immune cells gain access to the CNS across the blood-brain barrier to cause inflammation, myelin destruction, and neuronal damage. Here, we discovered that calnexin, an ER chaperone, is highly abundant in human brain endothelial cells of MS patients. Conversely, mice lacking calnexin exhibited resistance to EAE induction, no evidence of immune cell infiltration into the CNS, and no induction of inflammation markers within the CNS. Furthermore, calnexin deficiency in mice did not alter the development or function of the immune system. Instead, the loss of calnexin led to a defect in brain endothelial cell function that resulted in reduced T cell trafficking across the blood-brain barrier. These findings identify calnexin in brain endothelial cells as a potentially novel target for developing strategies aimed at managing or pre...
Calreticulin is an endoplasmic reticulum (ER) resident protein critical for maintaining Ca(2+) ho... more Calreticulin is an endoplasmic reticulum (ER) resident protein critical for maintaining Ca(2+) homeostasis and glycoprotein folding in the ER. The protein has also been identified on the cell surface of apoptotic and necrotic cells and implicated to play a role in immunogenic cell death and other extracellular functions. The molecular events that promote cell surface association of calreticulin are not clear. Under cell stress conditions (environmental, drug induced, hypoxia), calreticulin may be upregulated as it attempts to regulate cell survival, death or repair. The initial signaling mechanisms involved in these processes may be regulated by the unfolded protein response (UPR) and genome damage response (GDR) pathways. Area covered: Here, the phenomenon of cell surface calreticulin and its extracellular functions are discussed, with a major emphasis on the process of immunogenic cell death. The evidence of how cell surface calreticulin may act as a damage associated molecular pattern molecule is evaluated, in addition to how these properties of the protein can be exploited for therapeutic vaccine development, cancer treatment and mediating other inflammatory processes. In addition, clarification of calreticulin functions from its intracellular, cell surface, and extracellular locations are provided. Expert opinion: While the protein folding and immune-stimulatory properties of calreticulin can be exploited to develop therapies, the molecular pathways involved remain to be elucidated. Nevertheless, exploiting the multifaceted properties of calreticulin may in the future provide a means to treat a number of diseases.
The disruption of the energy or nutrient balance triggers endoplasmic reticulum (ER) stress, a pr... more The disruption of the energy or nutrient balance triggers endoplasmic reticulum (ER) stress, a process that mobilizes various strategies, collectively called the unfolded protein response (UPR), which reestablish homeostasis of the ER and cell. Activation of the UPR stress sensor IRE1α (inositol-requiring enzyme 1α) stimulates its endoribonuclease activity, leading to the generation of the mRNA encoding the transcription factor XBP1 (X-box binding protein 1), which regulates the transcription of genes encoding factors involved in controlling the quality and folding of proteins. We found that the activity of IRE1α was regulated by the ER oxidoreductase PDIA6 (protein disulfide isomerase A6) and the microRNA miR-322 in response to disruption of ER Ca2+ homeostasis. PDIA6 interacted with IRE1α and enhanced IRE1α activity as monitored by phosphorylation of IRE1α and XBP1 mRNA splicing, but PDIA6 did not substantially affect the activity of other pathways that mediate responses to ER str...
Biochimica et Biophysica Acta (BBA) - Molecular Cell Research, 2014
Myelin oligodendrocyte glycoprotein (MOG) is a type I integral membrane protein that is expressed... more Myelin oligodendrocyte glycoprotein (MOG) is a type I integral membrane protein that is expressed in the central nervous system. MOG has a single N-glycosylation site within its extracellular domain. MOG has been linked with pathogenesis of multiple sclerosis; anti-MOG antibodies have been detected in the sera of multiple sclerosis patients. N-glycosylation is an important post-translational modification of protein that might impact their folding, localization and function. However, the role of sugar in the biology of MOG is not well understood. In this study, we created a mutant MOG lacking N-linked glycan and tested its properties. We concluded that the lack of sugar did not impact on MOG abundance in the absence of endoplasmic reticulum molecular chaperone calnexin. We also show that the absence of N-glycan did not interfere with MOG's subcellular localization and it did not result in activation of endoplasmic reticulum stress. This article is part of a Special Issue entitled: 13th European Symposium on Calcium.
Canadian Journal of Physiology and Pharmacology, 2012
The endoplasmic reticulum has an intricate network of pathways built to deal with the secretory a... more The endoplasmic reticulum has an intricate network of pathways built to deal with the secretory and integral membrane protein synthesis demands of the cell, as well as adaptive responses set up for the endoplasmic reticulum to rely on when stressed. These pathways are both essential and complex, and because of these 2 factors, several situations can lead to a dysfunctional endoplasmic reticulum and result in a dysfunctional cell with the potential to contribute to the progression of disease. The endoplasmic reticulum has been implicated in several metabolic, neurodegenerative, inflammatory, autoimmune, and renal diseases and disorders, and in particular, cardiovascular diseases. The role of the endoplasmic reticulum in cardiovascular disease shows how the change in function of a particular microscopic organelle can lead to macroscopic changes in the form of disease.
Biochemical and Biophysical Research Communications, 2012
Our previous studies have demonstrated that prion protein (PrP) leads to disassembly of microtubu... more Our previous studies have demonstrated that prion protein (PrP) leads to disassembly of microtubular cytoskeleton through binding to tubulin and its oligomerization. Here we found that PrP-treated cells exhibited improper morphology of mitotic spindles. Formation of aberrant spindles may result not only from altered microtubule dynamics - as expected from PrP-induced tubulin oligomerization - but also from impairing the function of molecular motors. Therefore we checked whether binding of PrP to microtubules affected movement generated by Ncd - a kinesin responsible for the proper organization of division spindles. We found that PrP inhibited Ncd-driven transport of microtubules. Most probably, the inhibition of the microtubule movement resulted from PrP-induced changes in the microtubule structure since Ncd-microtubule binding was reduced already at low PrP to tubulin molar ratios. This study suggests another plausible mechanism of PrP cytotoxicity related to the interaction with tubulin, namely impeding microtubule-dependent transport.
Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease, 2012
Missense mutations in human TPM3 gene encoding γ-tropomyosin expressed in slow muscle type 1 fibe... more Missense mutations in human TPM3 gene encoding γ-tropomyosin expressed in slow muscle type 1 fibers, were associated with three types of congenital myopathies-nemaline myopathy, cap disease and congenital fiber type disproportion. Functional effects of the following substitutions: Leu100Met, Ala156Thr, Arg168His, Arg168Cys, Arg168Gly, Lys169Glu, and Arg245Gly, were examined in biochemical assays using recombinant tropomyosin mutants and native proteins isolated from skeletal muscle. Most, but not all, mutations decreased the affinity of tropomyosin for actin alone and in complex with troponin (±Ca(2+)). All studied tropomyosin mutants reduced Ca-induced activation but had no effect on the inhibition of actomyosin cross-bridges. Ca(2+)-sensitivity of the actomyosin interactions, as well as cooperativity of myosin-induced activation of the thin filament was affected by individual tropomyosin mutants with various degrees. Decreased motility of the reconstructed thin filaments was a result of combined functional defects caused by myopathy-related tropomyosin mutants. We conclude that muscle weakness and structural abnormalities observed in TPM3-related congenital myopathies result from reduced capability of the thin filament to fully activate actin-myosin cross-bridges.
Kinesins form a large and diverse superfamily of proteins involved in numerous important cellular... more Kinesins form a large and diverse superfamily of proteins involved in numerous important cellular processes. The majority of them are molecular motors moving along microtubules. Conversion of chemical energy into mechanical work is accomplished in a sequence of events involving both biochemical and conformational alternation of the motor structure called the mechanochemical cycle. Different members of the kinesin superfamily can either perform their function in large groups or act as single molecules. Conventional kinesin, a member of the kinesin-1 subfamily, exemplifies the second type of motor which requires tight coordination of the mechanochemical cycle in two identical subunits to accomplish processive movement toward the microtubule plus end. Recent results strongly support an asymmetric handover hand model of ''walking'' for this protein. Conformational strain between two subunits at the stage of the cycle where both heads are attached to the microtubule seems to be a major factor in intersubunit coordination, although molecular and kinetic details of this phenomenon are not yet deciphered. We discuss also current knowledge concerning intersubunit coordination in other kinesin subfamilies. Members of the kinesin-3 class use at least three different mechanisms of movement and can translocate in monomeric or dimeric forms. It is not known to what extent intersubunit coordination takes place in Ncd, a dimeric member of the kinesin-14 subfamily which, unlike conventional kinesin, exercises a power-stroke toward the microtubule minus end. Eg5, a member of the kinesin-5 subfamily is a homotetrameric protein with two kinesin-1-like dimeric halves controlled by their relative orientation on two microtubules. It seems that diversity of subunit organization, quaternary structures and cellular functions in the kinesin superfamily are reflected also by the divergent extent and mechanism of intersubunit coordination during kinesin movement along microtubules.
A novel 120 kDa actin-binding protein (ApABP-F1) was found in Amoeba proteus. It was distributed ... more A novel 120 kDa actin-binding protein (ApABP-F1) was found in Amoeba proteus. It was distributed throughout the cytoplasm, mainly in the subplasma membrane and perinuclear–nuclear areas, enriched in actin. The full-length cDNA of ApABP consisted of 2672 nucleotides with an open reading frame of 878 amino acids, giving a *95 kDa protein with a theoretical pI value of 5.11. It had a novel domain organization pattern: the N terminus (residues 1–104) contained 1 calponin-homology (CH) domain, followed by only 1 region that was homologous to the filamin repeat (FR, residues 209–324), and a central region (residues 344–577) exhibiting a very high probability of coiled-coil formation, probably engaged in the observed protein dimerization. A phylogenetic tree constructed for CH domains from 25 various proteins revealed that the CH domain of ApABP was most related to that of the hypothetical mouse KIAA0903-like protein , whereas not much relationship to either filamins or the gelation factor (ABP-120) of Dictyostelium discoideum and Entamoeba histolytica was found. Résumé : Une nouvelle protéine de 120 kDa liant l'actine (ApABP) a e ´té identifiée chez Amoeba proteus. Elle e ´tait distri-buée a ` travers tout le cytoplasme, particulièrement dans la région sous la membrane plasmique ainsi que dans les régions périnucléaire et nucléaire enrichies en actine. L'ADNc de pleine longueur de ApABP comprenait 2672 nucléotides et un cadre de lecture ouvert de 878 acides aminés, résultant en une protéine d'environ 95 kDa dont le pI théorique e ´tait de 5.11. Ses domaines e ´taient organisés selon un nouveau patron : l'extrémité N terminale (résidus 1–104) contenait un do-maine homologue a ` la calponine (CH), suivi par une seule région homologue aux répétitions de filamine (FR, résidus 209-324), et une région centrale (résidus 344–577) formant probablement un domaine «coiled-coil», potentiellement impliqué dans la dimérisation observée de la protéine. L'arbre phylogénique des domaines CH construit a ` partir de 25 protéines a révélé que le domaine CH de ApABP e ´tait le plus apparenté au domaine CH d'une protéine hypothétique ressemblant a ` KIAA0903 chez la souris, alors que peu de relation avec les filamines ou avec les facteurs de gélification ABP-120 de Dictyostelium discoideum et d'Entamoeba histolytica n'e ´tait trouvée.
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