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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Two crystal forms (P6(3) and R3) of human annexin V have been crystallographically refined at 2.3 A and 2.0 A resolution to R-values of 0.184 and 0.174, respectively, applying very tight stereochemical restraints with deviations from ideal geometry of 0.01 A and 2 degrees. The three independent molecules (2 in P6(3), 1 in R3) are similar, with deviations in C alpha positions of 0.6 A. The polypeptide chain of 320 amino acid residues is folded into a planar cyclic arrangement of four repeats. The repeats have similar structures of five alpha-helical segments wound into a right-handed compact superhelix. Three calcium ion sites in repeats I, II and IV and two lanthanum ion sites in repeat I have been found in the R3 crystals. They are located at the convex face of the molecule opposite the N terminus. Repeat III has a different conformation at this site and no calcium bound. The calcium sites are similar to the phospholipase A2 calcium-binding site, suggesting analogy also in phospholipid interaction. The center of the molecule is formed by a channel of polar charged residues, which also harbors a chain of ordered water molecules conserved in the different crystal forms. Comparison with amino acid sequences of other annexins shows a high degree of similarity between them. Long insertions are found only at the N termini. Most conserved are the residues forming the metal-binding sites and the polar channel. Annexins V and VII form voltage-gated calcium ion channels when bound to membranes in vitro. We suggest that annexins bind with their convex face to membranes, causing local disorder and permeability of the phospholipid bilayers. Annexins are Janus-faced proteins that face phospholipid and water and mediate calcium transport.
J Mol Biol 1992 Feb 05
PMID:Crystal and molecular structure of human annexin V after refinement. Implications for structure, membrane binding and ion channel formation of the annexin family of proteins. 131 70

Annexin VI is an eight repeat member of the annexin family of proteins which are both water soluble and bind to negatively charged phospholipids in a calcium-dependent manner. Here we present a model for annexin VI based on fitting the three-dimensional structure of two annexin V molecules (Huber (1990) EMBO J. 9, 3867-3874) to the two-dimensional stain-excluding density of lipid-bound annexin VI (Newman (1989) J. Mol. Biol. 206, 213-219). Both annexin VI lobes could only be fitted with their convex faces closest to the lipid monolayer. This supports the hypothesis that annexin-lipid binding is mediated by the interaction between calcium bound to the loops protruding from the convex protein surface and phospholipid headgroups.
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PMID:A model of the structure of human annexin VI bound to lipid monolayers. 138 88

Stimulation of cardiac phospholipid metabolism has diverse biological effects, ranging from subtle changes in cellular function to severe cellular damage. Accordingly, knowledge of the factors governing the activity of cardiac phospholipases is of great biological importance. A possible role of annexins, intracellular proteins that bind to membranes in a calcium dependent manner, as modulators of phospholipase activity has been proposed. In this study we investigated the cell type specific distribution of Annexin V and VIII in the heart. Recombinant Annexin V was used to examine the effect of this type of Annexin on cardiac phospholipase activity. Western blot analysis shows that annexin V is abundantly present in the heart. Using isolated myocytes and cultured cardiac endothelial and fibroblast-like cells, it is demonstrated that the localization of Annexin V is confined to non-myocytes. No positive bands matching the Mw of recombinant Annexin VIII are found in any of the cell types examined. In vitro studies demonstrate that recombinant Annexin V potently inhibits the activity of cardiac membrane-bound phospholipases, acting on their natural surrounding substrate, in a calcium dependent manner. Interestingly, annexin V also inhibits triacylglycerol hydrolysis. In conclusion, the expression of annexins is cell-type specific and suggests a cell-type specific function of these proteins in the heart. The absence of Annexin V in cardiac myocytes dismisses involvement of this annexin in cardiomyocyte phospholipid metabolism. The presence of Annexin V in cardiac endothelial and fibroblasts suggests a regulating role in the phospholipid homeostasis of non-myocyte cell types in the heart.
Mol Cell Biochem 1992 Oct 21
PMID:Annexins in cardiac tissue: cellular localization and effect on phospholipase activity. 148 Jan 59

Annexins are a family of water-soluble proteins that bind to membranes in a calcium-dependent manner. Some members have been shown to exhibit voltage-dependent calcium channel activity, a property characteristic of integral membrane proteins. The structures of human annexin V in crystals obtained from aqueous solution and in two-dimensional crystals when bound to phospholipid layers have been determined by X-ray and electron crystallography, respectively. They are compared here. Both structures show close correspondence, suggesting that annexins attach to phospholipid membranes without substantial structural change. These observations, together with biochemical data, lead to the conclusion that annexin V interacts with phospholipid membranes with its convex face. We propose that binding is mediated by direct interaction between the phosphoryl headgroups and the calcium bound to polypeptide loops protruding from the convex face. The membrane area covered by annexin may thus become disordered and permeable allowing calcium flux through the membrane and the central channel-like structure found in annexin molecules.
J Mol Biol 1991 Jul 20
PMID:Structure of soluble and membrane-bound human annexin V. 183 Mar 42

We have previously reported the isolation of a hydrophobic, type-II collagen-binding glycoprotein of molecular weight 31,000 (31,000-mol-wt protein) from chick chondrocyte membranes (Mollenhauer, J., and K. von der Mark, EMBO Eur. Mol. Biol. Organ. J., 2:45-50). The function of this protein in anchoring pericellular type II collagen to the chondrocyte surface was inferred from its ability to bind native type-II collagen either when detergent solubilized or when inserted into liposomes. In the present study we have used specific antibodies to localize this protein, which we now call anchorin CII, to the surface of chondrocytes in both cartilage sections, and in cell culture. In immunofluorescence studies of isolated chondrocytes we observed a dense, punctate distribution of anchorin CII on the cell surface when chondrocytes were enclosed by a pericellular type II collagen matrix. Removal of the pericellular matrix with trypsin also removed anchorin CII. The membrane protein character of anchorin CII was indicated by the demonstration of antibody-induced patching and capping on the chondrocyte surface at 22 degrees C and 37 degrees C, respectively. In monolayer culture, the amount of anchorin CII appeared reduced on flattened chondrocytes lacking a pericellular type II collagen matrix but was prominent upon intercellular cell processes. Fab' fragments prepared from either anchorin CII antiserum or an antiserum directed against the entire chondrocyte membrane inhibited the attachment of chondrocytes to a type II collagen substrate. In each case, the inhibition of attachment was neutralized by preincubation of Fab' fragments with purified anchorin CII.
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PMID:Role of anchorin CII, a 31,000-mol-wt membrane protein, in the interaction of chondrocytes with type II collagen. 632 73

Annexins are a family of proteins with calcium- and phospholipid-binding properties. The present study was performed to identify which members of the annexin family are present in rat heart and to determine the cellular and subcellular distribution of annexin V, the most prominent annexin in rat cardiac tissue, in isolated ventricular myocytes and cultured endothelial and fibroblast-like cells. The presence of annexin I plus II, III, IV, V and VI in rat cardiac tissue was positively established with western blot analysis. Immunohistochemistry and western blot analysis revealed that annexin V is present in both cardiomyocytes and non-myocytal cells of the heart. In endothelial cells and fibroblast-like cells annexin V is predominantly localized in the cytoplasm and in cardiac myocytes in close vicinity of the sarcolemma. This last finding is confirmed by electron microscopy. Northern blot analysis demonstrated that all cell types investigated showed expression of annexin V. Annexin V mRNA levels were highest in the fibroblast-like cells, followed by the endothelial cells, and a weak signal was observed in the cardiomyocytes. By means of a sandwich-type enzyme-linked immunosorbent assay (ELISA) annexin V content in intact adult rat heart, isolated myocytes, cultured cardiac endothelial cells and fibroblast-like cells was found to be 0.70, 0.17, 1.63 and 3.84 micrograms/mg total protein, respectively. The differences in subcellular localization of annexin V in myocytes and non-myocytes suggest differences in biological function of annexin V in the various cell types.
J Mol Cell Cardiol 1995 Jan
PMID:Annexin V in the adult rat heart: isolation, localization and quantitation. 776 Mar 55

This study addresses the roles of individual annexin IV domains in calcium-dependent membrane binding and aggregation through an analysis of the activities of mutant annexin IV proteins in which critical residues in one or more domains have been altered. The consensus sequence for high-affinity Ca(2+)-binding pockets obtained from the annexin V crystal structure is GXGT-38 residues-D/E [Huber, R., et al. (1992) J. Mol. Biol. 223, 683-704]. Site-directed mutagenesis was used to change the conserved acidic residues (D/E) in these sequences to alanine residues in each of the four domains of bovine annexin IV, singly or in combinations. Fourteen mutants with one, two, three, or four mutated domains were constructed and expressed in Escherichia coli. Purified recombinant product was evaluated for Ca(2+)-dependent binding to and aggregation of bovine chromaffin granules. Increases in the number of mutated domains resulted in increased Ca2+ requirements for both granule binding and aggregation. Further analysis revealed that mutations in individual domains had preferential effects on the binding or aggregating activities of the protein. For example, mutation of the first or fourth domains had a greater effect on membrane binding than aggregation, while conversely, mutation of the second domain had a more dramatic effect on membrane aggregation. Mutation of the third domain was largely silent in these assays. An additional mutation was made in the fourth domain to substitute a serine for a highly conserved arginine residue (Arg274) present at the C-terminus of the fourth endonexin fold. This mutation increased the calcium requirement for membrane binding 2-fold and for membrane aggregation 3-fold. This mutant protein was found to be an effective inhibitor of membrane aggregation by native annexin IV at intermediate levels of calcium.
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PMID:Combinatorial mutagenesis of the four domains of annexin IV: effects on chromaffin granule binding and aggregating activities. 789 24

The cellular and subcellular localization of annexins V and VI, two members of a superfamily of Ca(2+)-dependent phospholipid- and membrane-binding proteins, was investigated in chorionic villi of human placentae of different gestational ages by postembedding immunocytochemistry at the electron microscope level. All cell types of placental villi, i.e., the syncytiotrophoblast, Langhans cells, Hofbauer cells, fibroblasts, and capillary endothelial cells, appeared to express the two proteins, irrespective of the gestational age. By immunogold particle counts, annexin V was observed to be 2-3 times as much abundant as annexin VI. Syncytiotrophoblast cells appeared to contain the largest amounts and Langhans cells appeared to contain the least amounts of annexins V and VI, as judged by immunocytochemistry. The two proteins were found associated with plasma, Golgi, and vacuolar membranes, and with membranes of the endoplasmic reticulum, as well as diffusely in the cytoplasm. Annexin V appeared to be distributed in nearly equal proportions between cell membranes and the cytoplasm in stromal cells and to be about 30% associated with cell membranes in trophoblast cells, whereas annexin VI appeared almost equally distributed between cell membranes and the cytoplasm in trophoblast and stromal cells. Also, annexins V and VI appeared to be more abundant in trophoblast cells than in stromal cells. The present data strongly support the idea that placenta is a preferential site of annexin-regulated activities, and suggest that annexins V and VI are actively involved in the Ca(2+)-dependent regulation of membrane processes in trophoblast cells.
Cell Mol Biol Res 1993
PMID:Immunocytochemical localization of annexins V and VI in human placentae of different gestational ages. 801 49

Annexins are intracellular proteins which bind to membranes in a Ca(2+)-dependent manner and which have been proposed to play regulatory roles in different membrane processes. In the present study, the stoichiometry of the Ca(2+)-dependent binding of annexin V to phosphatidylserine molecules incorporated into liposomes was studied by fluorescence spectroscopy. The Ca(2+)-dependence of the binding was determined using liposomes made of dioleoylphosphatidylserine (PS) and dioleoylphosphatidylcholine (PC), with a PC/PS molar ratio ranging from 1 to 800. These liposomes were shown to be mostly unilamellar by cryoelectron microscopy. [Ca2+]1/2 concentrations required for half-maximal binding of annexin V range from 57 microM at PC/PS = 1 up to 96 mM at PC/PS = 800. Titration of accessible PS molecules showed that annexin V molecules bind equally well to liposomes of PC/PS ratio ranging from 1 to 400. The stoichiometry of the binding between annexin V and PS, determined at low PS content, is eight annexin V molecules per one PS molecule. We propose a novel model of the Ca(2+)-dependent interaction between annexin V and lipid membranes, based on the formation of two-dimensional arrays of annexin V molecules, stabilized by both protein-lipid and protein-protein interactions.
J Mol Biol 1994 Feb 11
PMID:Formation of two-dimensional arrays of annexin V on phosphatidylserine-containing liposomes. 810 5

Annexin V binds to phospholipids in a calcium-dependent manner and exhibits calcium channel activity in vitro. We prepared a variety of mutants yielding information about the structure-function relationship of the ion channel activity. All mutants were characterized by X-ray crystallography, electron microscopy and electrophysiological measurements. Their structures are insignificantly changed whereas their electrophysiological properties are drastically different. Glu95, located in the central hydrophilic pore of the molecule, is crucial for the ion selectivity filter as its exchange leads to reduced calcium and increased sodium conductance. The removal of Glu17, located on the protein surface and far from the ion conduction pathway, leads to the appearance of a second conductance level of 9 pS in addition to the conductance level of about 30 pS in the wild-type molecule. This was also the case for Glu78, which is part of a weak calcium binding site. The exchange of Glu17 and Glu78 produced a mutant retaining only the smaller conductance level. We conclude that these two residues influence the angle between the two halves of the molecule, which determines the diameter of the ion conduction pathway, thereby leading to the occurrence of a second conductance level.
J Mol Biol 1994 Apr 08
PMID:Structural and electrophysiological analysis of annexin V mutants. Mutagenesis of human annexin V, an in vitro voltage-gated calcium channel, provides information about the structural features of the ion pathway, the voltage sensor and the ion selectivity filter. 815 7


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