The amino acid sequence of protein II and its phosphorylation site for protein kinase C; the domain structure Ca2+-modulated lipid binding proteins

Regulation of the Equilibrium between Closed and Open Conformations of Annexin A2 by N-Terminal Phosphorylation and S100A4-Binding

Annexin A2 (ANXA2) has a versatile role in membrane-associated functions including membrane aggregation, endo- and exocytosis, and it is regulated by post-translational modifications and protein-protein interactions through the unstructured N-terminal domain (NTD). Our sequence analysis revealed a short motif responsible for clamping the NTD to the C-terminal core domain (CTD). Structural studies indicated that the flexibility of the NTD and CTD are interrelated and oppositely regulated by Tyr24 phosphorylation and Ser26Glu phosphomimicking mutation. The crystal structure of the ANXA2-S100A4 complex showed that asymmetric binding of S100A4 induces dislocation of the NTD from the CTD and, similar to the Ser26Glu mutation, unmasks the concave side of ANXA2. In contrast, pTyr24 anchors the NTD to the CTD and hampers the membrane-bridging function. This inhibition can be restored by S100A4 and S100A10 binding. Based on our results we provide a structural model for regulation of ANXA2-mediated membrane aggregation by NTD phosphorylation and S100 binding.

Annexin A4 self-association modulates general membrane protein mobility in living cells

Annexins are Ca2+-regulated phospholipid-binding proteins whose function is only partially understood. Annexin A4 is a member of this family that is believed to be involved in exocytosis and regulation of epithelial Cl- secretion. In this work, fluorescent protein fusions of annexin A4 were used to investigate Ca2+-induced annexin A4 translocation and self-association on membrane surfaces in living cells. We designed a novel, genetically encoded, FRET sensor (CYNEX4) that allowed for easy quantification of translocation and self-association. Mobility of annexin A4 on membrane surfaces was investigated by FRAP. The experiments revealed the immobile nature of annexin A4 aggregates on membrane surfaces, which in turn strongly reduced the mobility of transmembrane and plasma membrane associated proteins. Our work provides mechanistic insight into how annexin A4 may regulate plasma membrane protein function.

Intron disruption of the annexin IV gene reveals novel transcripts

Annexin IV (AIV), a Ca2+-dependent membrane-binding protein, is expressed in many epithelia. Annexin IV modifies membrane bilayers by increasing rigidity, reducing water and H+ permeability, promoting vesicle aggregation, and regulating ion conductances, all in a Ca2+-dependent manner. We have characterized a mouse in which a gene trap has been inserted into the first intron of annexin IV. Processing of the primary transcript is disrupted. Northern blot and immunoblot data indicated that annexin IV expression was eliminated in many but not all tissues. Immunohistochemical analysis, however, demonstrated that annexin IV expression was eliminated in some cell types, but was unaltered in others. 5'-Rapid amplification of cDNA ends analysis of intestinal and kidney RNA revealed three transcripts, AIVa, AIVb, and AIVc. AIVa is widely distributed. AIVb is expressed only in the digestive tract. AIVc expression is very restricted. A selected number of epithelial cells of unique morphology demonstrate high concentrations. All three transcripts produce an identical annexin IV protein. The different tissue and cell-specific expression profiles of the three transcripts suggest that regulation of both the annexin IV gene expression and the cellular role of the protein are complex. The AIVa-/- mouse may become a valuable model to further study transcription and the physiological role of annexin IV.

Protein kinase C alpha-dependent phosphorylation of Golgi proteins

Golgi-enriched membranes were phosphorylated in order to understand the mechanism for protein kinase C (PKC) regulation of exocytic vesicle formation at the trans-Golgi network. Two of the main PKC substrates were identified as MARCKS and Mac-MARCKS by two-dimensional electrophoresis (2-DE) and mass spectrometric sequencing. Annexin IV and profilin I, two other Golgi-associated proteins--although known as in vitro PKC substrates--were not phosphorylated in the Golgi-bound state.

Characterization and developmentally regulated expression of four annexins in the killifish medaka

Annexins are Ca2+-regulated membrane binding proteins implicated in a wide range of membrane-related and signal transduction events, including the endocytosis of membrane receptors and Ca2+-regulated as well as constitutive secretion. To date, 10 unique members of this multigene family have been identified in a variety of cell types and tissues of higher vertebrates, with different members showing distinct tissue distributions in the adult organisms. To establish whether annexins also function in embryonic development, we analyzed the expression pattern during vertebrate morphogenesis using the medaka fish Oryzias latipes as a model system. From a larval medaka cDNA library, we isolated four types of clones, which were shown by sequence analysis to encode four different annexins (herein referred to as max 1-4). A comparison with known annexin sequences in the databases revealed that two medaka annexins (max 1 and 2) are highly similar in sequence to mammalian annexins V and IV, respectively, whereas the other two medaka annexins (max 3 and 4) are probably novel members of the family most closely related to mammalian annexins I and XI. Using whole-mount RNA in situ hybridization, we showed that the expression of the different medaka annexins during embryogenesis was strictly regulated at both the spatial and the temporal level. High levels of max 1, 2, and 3 transcripts were present in the developing stomach, gut, liver, air-bladder, and rectum during somitogenesis, thus identifying the digestive tract as the prime region of annexin expression. Interestingly, two structures playing crucial roles in neuronal patterning showed a distinct expression of annexins. The mesendoderm of the anterior prechordal plate of neurula-stage embryos was a site of max 4 transcription, and the floor plate of somitogenesis-stage embryos showed expression of max 2 and 3 to differing rostrocaudal extends along the brain and spinal cord. These results suggest specific functions of different annexins during vertebrate morphogenesis.

Crystal structure of bovine annexin VI in a calcium-bound state

The crystal structure of a calcium-bound form of bovine annexin VI has been determined with X-ray diffraction data to 2.9 A by molecular replacement. Six Ca2+ ions were found, five in AB loops, one in a DE loop. Two loops (II-AB, which binds calcium, and V-AB, which does not) have conformations that differ significantly from those in calcium-free, human recombinant annexin VI. There are only small differences between the calci- and the apo-annexin VI in the rest of the molecule. Calcium by itself does not promote a major conformational change.

Crystal structure of annexin V with its ligand K-201 as a calcium channel activity inhibitor

The crystal structure of recombinant human annexin V complexed with K-201, an inhibitor of the calcium ion channel activity of annexin V, was solved at 3.0 A by molecular replacement including the apo and high-calcium forms. K-201 was bound at the hinge region cavity formed by the N-terminal strand and domains II, III and IV, at the side opposite the calcium and membrane-binding surface, in an L-shaped conformation. Based on the complex and other annexin structures, K-201 is proposed to restrain the hinge movement of annexin V in an allosteric manner, resulting in the inhibition of calcium movement across the annexin V molecule.

The relationship between the binding of ATP and calcium to annexin IV. Effect of nucleotide on the calcium-dependent interaction of annexin with phosphatidylserine

With the use of ATP analogues, we have found that porcine liver annexin (Anx) IV can be covalently labelled with 8-azido[gamma-32P]-ATP in the presence of Ca2+ (Kd 4.2 microM) and that the labelling is prevented by asolectin/cholesterol liposomes or chelation of calcium ions. On the other hand, non-covalent binding of 2'-(or 3')-O-(2,4,6-trinitrophenyl)adenosine 5'-triphosphate (TNP-ATP) to AnxIV occurs optimally in the presence of liposomes and Ca2+ (Kd 7 microM). These observations were further confirmed by the results of intrinsic fluorescence quenching of AnxIV with various nucleotides, suggesting the existence of a relationship between Ca(2+)-, phospholipid- and ATP-binding sites within the annexin molecule. The interaction of AnxIV with nucleotides does not significantly affect its in vitro properties concerning the binding to phosphatidylserine (PS) monolayers.

Fluorescence spectroscopic studies on interactions between liver annexin VI and nucleotides--a possible role for a tryptophan residue

Annexin VI is a 68-kDa calcium-, phospholipid-, and cytoskeletal-element-binding protein, which has been implicated in various processes, including calcium release and sequestration in calcifying cartilage, in a receptor-mediated endocytosis in human fibroblasts, and in secretion from chromaffin granules. In these processes it was found that, in addition to Ca2+ and annexin, the presence of ATP is also a prerequisite. In the present report we show that annexin VI binds ATP and the binding of nucleotide to protein is accompanied by quenching of an intrinsic fluorescence of annexin VI, which was found to be specific for 2'-(or 3')-O-(2,4,6-trinitrophenyl)adenosine 5'-triphosphate, GTP and ATP, and dependent on the annexin conformation. The nucleotide-binding site within an annexin VI molecule is likely to be close to the tryptophan-containing domain of annexin VI. We propose that ATP plays the role of a physiological ligand for annexin VI, and its binding to annexin VI may represent an alternative cellular mechanism for the regulation of annexin-membrane interactions coupled to overall energy transitions in the cell.

Annexins II, IV, V and VI relocate in response to rises in intracellular calcium in human foreskin fibroblasts

Annexins are a family of proteins implicated in a number of cellular processes involving calcium. We studied annexins I, II, IV, V and VI and found that they are all present in human foreskin fibroblasts and, from immunocytochemical studies, have distinct locations in the cell. Only annexin IV and annexin V have unstructured cytoplasmic staining patterns consistent with predominantly cytosolic locations. Annexin VI partially colocalizes with the endoplasmic reticulum. In contrast, annexins I and II are both associated with the plasma membrane with annexin II having a very homogeneous staining compared with the punctate pattern observed for annexin I. Annexins I, IV and V are all present in the nucleus at higher concentrations than in the cytoplasm. Treatment of cells with the calcium ionophore A23187 to raise intracellular calcium, results in relocations of annexin II, IV, V and VI. Intranuclear annexins IV and V relocate to the nuclear membrane whereas the cytosolic pools of these annexins relocate to the plasma membrane. Annexin II relocates to granular structures at the plasma membrane whereas annexin VI relocates to a more homogeneous distribution on the plasma membrane. These results are consistent with an important role for annexins in mediating the calcium signal at the plasma membrane and within the nuclei of fibroblasts.

Distribution of annexins I, II, and IV in bovine mammary gland

Annexins belong to a family of proteins that are characterized by their ability to bind phospholipids in a Ca(2+)-dependent manner that is thought to be involved in a variety of biological processes. The present study determined the localization of annexins in subcellular fractions, nuclei in particular, of cow mammary gland by immunoblot analysis using monoclonal antibodies to annexins I, II, IV, and VI. The analysis revealed that annexins I, II, and IV were present in cytosol, but VI was not. Annexins I and IV were found in the nuclear fraction, but annexin II was only faintly present. Annexin VI was also undetectable in this fraction. Cytosolic annexin I had a molecular mass of 36 kDa. The 36-kDa annexin I was also found in the nuclear fraction. A 38-kDa annexin I was additionally detected in nuclei. The cytosolic and nuclear 36-kDa annexin I and the nuclear 38-kDa annexin I showed different isoelectric points, as revealed by two-dimensional PAGE. Annexin IV from cytosolic and nuclear fractions had similar molecular masses and isoelectric points.

Annexin II tetramer: structure and function

The annexins are a family of proteins that bind acidic phospholipids in the presence of Ca2+. The interaction of these proteins with biological membranes has led to the suggestion that these proteins may play a role in membrane trafficking events such as exocytosis, endocytosis and cell-cell adhesion. One member of the annexin family, annexin II, has been shown to exist as a monomer, heterodimer or heterotetramer. The ability of annexin II tetramer to bridge secretory granules to plasma membrane has suggested that this protein may play a role in Ca(2+)-dependent exocytosis. Annexin II tetramer has also been demonstrated on the extracellular face of some metastatic cells where it mediates the binding of certain metastatic cells to normal cells. Annexin II tetramer is a major cellular substrate of protein kinase C and pp60src. Phosphorylation of annexin II tetramer is a negative modulator of protein function.

Modulation of p36 gene expression in human neuronal cells

p36 is a calcium/lipid-binding phosphoprotein that is expressed at high levels in proliferating and transformed cells, and at low levels in terminally differentiated cells, such as CNS neurons. The calcium-dependent binding to membrane phospholipids, and its capacity to interact with intermediate filament proteins suggest that p36 may be involved in the transduction of extracellular signals. The present work examines p36 gene expression in the mature CNS, primary primitive neuroectodermal tumors (PNETs), and transformed PNET cell lines. p36 immunoreactivity was not observed in normal adult human brain, but low levels of the protein were detected by Western blot analysis. Following acute anoxic cerebral injury, the mean levels of p36 protein were elevated two-fold, and injured neurons exhibited increased p36 immunoreactivity. This phenomenon was likely to have been mediated by post-transcriptional mechanisms since there was no corresponding change in the level p36 mRNA. p36 immunoreactivity was detected in 8 of 9 primary PNETs, and in 3 of 3 neurofilament-expressing PNET cell lines. The levels of p36 protein in PNET cell lines were 5-fold higher than in adult human brain tissue. Although p36 gene expression was generally high in proliferating PNET cells, the levels of p36 mRNA and protein were not strictly correlated with DNA synthesis. Instead, p36 gene expression was modulated in both proliferating and non-proliferating PNET cell cultures by treatment with 50 mIU/ml of insulin, 100 mM ethanol, or 5 microM retinoic acid. The frequent discordances observed experimentally and in vivo between p36 mRNA and p36 protein expression suggest that the steady-state levels of p36 protein in neuronal cells may be regulated primarily by post-transcriptional mechanisms.

Expression and characterization of a Dictyostelium discoideum annexin

The annexins are calcium-dependent phospholipid-binding proteins. Recently the gene encoding the homologue of a mammalian annexin has been identified in Dictyostelium discoideum. Analysis of cDNA and genomic clones showed that the transcript for Dictyostelium annexin is alternatively spliced (Greenwood, M. and Tsang, A. (1991) Biochim. Biophys. Acta 1088, 429-432; Döring, V., Schleicher, M and Noegel, A. (1991) J. Biol. Chem. 266, 17509-17515). Here, we showed that the Dictyostelium annexin DNA hybridized to two populations of transcripts. We used a recombinant annexin polypeptide to raise polyclonal antibody. Immunoblot analysis revealed that the antibody recognized two polypeptides of 48 kDa and 54 kDa in developing D. discoideum cells. The molecular sizes of these polypeptides correspond well with the expected sizes of the alternatively spliced products. The 48-kDa and 54-kDa polypeptides were purified by isoelectric focusing to more than 70% homogeneity. The partially purified proteins were found to associate with phosphatidylserine vesicles in a calcium-dependent manner. These results suggest that the 48- and 54-kDa polypeptides are the products of alternative splicing of the annexin transcripts. During development the two polypeptides accumulate at different rates to about 60 times the level detected in vegetative cells. On the other hand, RNA blot analysis showed that the level of the annexin transcripts in multicellular aggregates was about 5 times that of vegetative cells.

A new function of calphobindin I (annexin V). Promotion of both migration and urokinase-type plasminogen activator activity of normal human keratinocytes

Calphobindin I (CPB-I, annexin V) is an anticoagulant protein purified from human placenta; it is a member of the annexin family that binds phospholipids in a calcium-dependent manner. In this study, we discovered and examined a new function of CPB-I: promotion of both the migration and the urokinase-type plasminogen activator (uPA) activity of normal human keratinocytes (NHK). While the treatment of NHK with a 10-micrograms/ml concentration of CPB-I for 24 h or 48 h caused an approximate 30% increase in the migration of NHK (compared with the no treatment), migration was inhibited when anti-CPB-I monoclonal antibodies (i.e. A46 and A180) were added along with the CPB-I. Moreover, while the treatment of NHK with a CPB-I concentration greater than 10 micrograms/ml caused a significant increase in the activity of secreted uPA, reflected in an approximately 40% increase in cell migration, uPA activity was inhibited both by cycloheximide and by monoclonal antibodies. This significant increase of secreted uPA was seen 8 h after the addition of CPB-I. Specific binding of CPB-I to NHK had a Kd value of 95.2 nM (equivalent to a CPB-I had no effect on NHK proliferation. Furthermore, CPB-I enhanced reepithelialization when it was applied locally twice a day to full-thickness cutaneous wounds made in male rats. Our results show that, during an injury, CPB-I helps reepithelialization through the promotion of both uPA synthesis and migration of keratinocytes without stimulating their proliferation.

Thrombin stimulates the intracellular relocation of annexin V in human platelets

Annexins are a family of proteins that have been implicated in a range of intracellular processes. In this paper we confirm the existence of annexin V in human platelets (0.02 +/- 0.005% of cell protein). We also demonstrate that 13.7 +/- 6.8% of intracellular annexin V becomes tightly associated with membranes in response to platelet activation by the physiological agonist thrombin and requires non-ionic detergent for solubilization. Thrombin stimulation also induces the association of annexin V (11.0 +/- 4.6% of the total) with the membrane in a manner which requires prolonged treatment with EGTA for its release from the membrane.

Comparison of [3H]WIN 35,428 binding, a marker for dopamine transporter, in embryonic mesencephalic neuronal cultures with striatal membranes of adult rats

In contrast to striatal membranes of adult rats, where high- (KD1 = 34 nM) and low- (KD2 = 48,400 nM) affinity binding sites for [3H]WIN 35,428 are present, in primary cultures of ventral mesencephalon neurons (CVMNs) only low-affinity binding sites were found (KD = 336,000 nM). The binding of [3H]WIN 35,428 in CVMNs prepared from rat embryos was reversible, saturable, and located in cytosol. Although dopamine (DA) uptake blockers inhibited [3H]DA uptake at nanomolar concentrations in CVMNs, the displacement of [3H]WIN 35,428 binding in CVMNs by DA uptake inhibitors required 100-8,000 times higher concentrations than were needed to displace [3H]WIN 35,428 binding in striatal membranes. Piperazine derivatives, e.g., GBR-12909, GBR-12935, and rimcazole, inhibited [3H]WIN 35,428 binding in CVMNs more effectively than did cocaine, WIN 35,428, mazindol, nomifensine, or benztropin. A positive correlation (r = 0.779; p < 0.001) was found between drug affinities for the striatal membrane sites labeled by [3H]WIN 35,428 and their abilities to inhibit DA uptake in CVMNs, whereas no correlation existed between the IC50 values of drugs that inhibited [3H]WIN 35,428 binding and [3H]DA uptake in CVMNs. The cytosolic [3H]WIN 35,428 binding sites may be a piperazine acceptor and may not be involved in the regulation of the DA transporter.

Novel isoforms of CaBP 33/37 (annexin V) from mammalian brain: structural and phosphorylation differences that suggest distinct biological roles

Two calcium-dependent phospholipid- and membrane-binding proteins have been purified from bovine brain. These are termed CaBP33 and CaBP37. Complete sequence analysis has revealed that these two proteins are isoforms of annexin V. Despite an apparent difference of 4 kDa between the two proteins on SDS-PAGE, only two amino-acid substitutions were found. These are, in CaBP33, Ser-36 and Lys-125 and in CaBP37, Thr-36 and Glu-125. This corresponds to a mass difference of 15 Da. This was confirmed by electrospray mass spectrometric analysis. Both isoforms can be phosphorylated substoichiometrically in vitro by protein kinase C at residue Thr-22.

Expression of anchorin CII, a collagen-binding protein of the annexin family, in the developing chick embryo

Expression of anchorin CII, a collagen-binding protein of the annexin family, was followed in the developing chick embryo using Northern and in situ hybridization and Western blotting. During chick somite development, anchorin CII mRNA was detected by Northern blotting as early as stage 11. At stage 24, anchorin mRNA accumulated in the anterior part of the somite sclerotome near the resegmentation line, as shown by in situ hybridization. The presence of anchorin CII protein during stages 11 to 20 was confirmed by Western blotting. In situ hybridization identified anchorin CII also in the otic vesicle adjacent to the site of contact with the statoacoustic ganglion and in the mandibular mesenchyme. The level of anchorin CII mRNA in differentiated hyaline cartilage, exemplified by sternal cartilage, was lower than that in differentiating somites or cultured chondrocytes. These findings are consistent with our notion that anchorin CII may be involved in cell-matrix interactions preceding chondrogenic differentiation events in the chick embryo. A significant level of anchorin CII mRNA and protein synthesis was also found in cultured myoblasts, but less than that in chondroblasts. This distribution pattern is different from that reported for a related protein, p34, or calpactin, the major protein substrate for tyrosine kinase phosphorylation in chick chondrocytes and fibroblasts. The results confirm suggestions from previous sequencing studies that anchorin CII and p34 are different proteins of the annexin/calpactin family.

Inhibition of protein kinase C by annexin V

Annexin V is a protein of unknown biological function that undergoes Ca(2+)-dependent binding to phospholipids located on the cytosolic face of the plasma membrane. Preliminary results presented herein suggest that a biological function of annexin V is the inhibition of protein kinase C (PKC). In vitro assays showed that annexin V was a specific high-affinity inhibitor of PKC-mediated phosphorylation of annexin I and myosin light chain kinase substrates, with half-maximal inhibition occurring at approximately 0.4 microM. Annexin V did not inhibit epidermal growth factor receptor/kinase phosphorylation of annexin I or cAMP-dependent protein kinase phosphorylation of the Kemptide peptide substrate. Since annexin V purified from both human placenta and recombinant bacteria inhibited protein kinase C activity, it is not likely that the inhibitor activity was associated with a minor contaminant of the preparations. The following results indicated that the mechanism of inhibition did not involve annexin V sequestration of phospholipid that was required for protein kinase C activation: similar inhibition curves were observed as phospholipid concentration was varied from 0 to 800 micrograms/mL; the extent of inhibition was not significantly affected by the order of addition of phospholipid, substrate, or PKC, and the core domain of annexin I was not a high-affinity inhibitor of PKC even though it had similar Ca2+ and phospholipid binding properties as annexin V. These data indirectly indicate that inhibition occurred by direct interaction between annexin V and PKC. Since the concentration of annexin V in many cell types exceeds the amounts required to achieve PKC inhibition in vitro, it is possible that annexin V inhibits PKC in a biologically significant manner in intact cells.

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

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.

Chromosomal mapping of the human annexin IV (ANX4) gene

Annexin IV (placental anticoagulant protein II) is a member of the annexin or lipocortin family of calcium-dependent phospholipid-binding proteins. A cDNA for human annexin IV was isolated from a placental library that is 675 bases longer in the 3' untranslated region than previously reported, indicating the existence of alternative mRNA processing for this gene. Genomic Southern blotting with a cDNA probe indicated a gene size of 18-56 kb. Primers developed for polymerase chain reaction (PCR) allowed amplification of a 1.6-kb portion of the ANX4 gene. DNA sequence analysis showed that this PCR product contained a single intron with exon-intron boundaries in exactly the same position as in the mouse annexin I and annexin II genes. PCR analysis of a somatic cell hybrid panel mapped the ANX4 gene to chromosome 2, and in situ hybridization with a cDNA probe showed a unique locus for ANX4 at 2p13. This study provides further evidence that genes for the annexins are dispersed throughout the genome but are similar in size and exon-intron organization.

Correlation of gene and protein structure of rat and human lipocortin I

Lipocortins (annexins) are a family of calcium-dependent phospholipid-binding proteins with phospholipase A2 inhibitory activity. The characteristic primary structure of members of this family consists of a core structure of four or eight repeated domains, which have been implicated in calcium-dependent phospholipid binding. In two lipocortins (I and II) a short amino-terminal sequence distinct from the core structure has potential regulatory functions which are dependent on its phosphorylation state. We have isolated the rat and the human lipocortin I genes and found that they both consist of 13 exons with a striking conservation of their exon-intron structure and their promoter and amino acid sequences. Both lipocortin I genes are at least 19 kbp in length with exons ranging from 57 to 123 bp interrupted by introns as large as 5 kbp. Each of the four repeat units of lipocortin I are encoded by two consecutive exons while individual exons code for the highly conserved putative calcium-binding domains. The promoter sequences in the rat and in human genes are highly conserved and contain nucleotide sequences characterized as enhancer sequences in other genes. The structure of the lipocortin I gene lends support to the hypothesis that the lipocortin genes arose by a duplication of a single domain.

Amino acid sequence analysis of the annexin super-gene family of proteins

The annexins are a widespread family of calcium-dependent membrane-binding proteins. No common function has been identified for the family and, until recently, no crystallographic data existed for an annexin. In this paper we draw together 22 available annexin sequences consisting of 88 similar repeat units, and apply the techniques of multiple sequence alignment, pattern matching, secondary structure prediction and conservation analysis to the characterisation of the molecules. The analysis clearly shows that the repeats cluster into four distinct families and that greatest variation occurs within the repeat 3 units. Multiple alignment of the 88 repeats shows amino acids with conserved physicochemical properties at 22 positions, with only Gly at position 23 being absolutely conserved in all repeats. Secondary structure prediction techniques identify five conserved helices in each repeat unit and patterns of conserved hydrophobic amino acids are consistent with one face of a helix packing against the protein core in predicted helices a, c, d, e. Helix b is generally hydrophobic in all repeats, but contains a striking pattern of repeat-specific residue conservation at position 31, with Arg in repeats 4 and Glu in repeats 2, but unconserved amino acids in repeats 1 and 3. This suggests repeats 2 and 4 may interact via a buried saltbridge. The loop between predicted helices a and b of repeat 3 shows features distinct from the equivalent loop in repeats 1, 2 and 4, suggesting an important structural and/or functional role for this region. No compelling evidence emerges from this study for uteroglobin and the annexins sharing similar tertiary structures, or for uteroglobin representing a derivative of a primordial one-repeat structure that underwent duplication to give the present day annexins. The analyses performed in this paper are re-evaluated in the Appendix, in the light of the recently published X-ray structure for human annexin V. The structure confirms most of the predictions and shows the power of techniques for the determination of tertiary structural information from the amino acid sequences of an aligned protein family.

Regulation of the sarcoplasmic reticulum Ca(2+)-release channel requires intact annexin VI

Annexin VI has eight highly conserved repeated domains; all other annexins have four. Díaz-Muñoz et al. (J Biol Chem 265:15894, 1990) reported that annexin VI alters the gating properties of the ryanodine-sensitive Ca(2+)-release channel isolated from sarcoplasmic reticulum. The investigate the domain structure of rat annexin VI (67 kDa calcimedin) required for this channel regulation, various proteolytic digestions were performed. In each case, protease-resistant core polypeptides were produced. Annexin VI was digested with V8 protease and two core polypeptides were purified by Ca(2+)-dependent phospholipid binding followed by HPLC. The purified fragments were shown to be derived from the N- and C-terminal halves of annexin VI, and demonstrated differential immunoreactivity with monoclonal antibodies to rat annexin VI. While both core polypeptides retained their ability to bind phospholipids in a Ca(2+)-dependent manner, they did not regulate the sarcoplasmic reticulum Ca(2+)-dependent manner, they did not regulate the sarcoplasmic reticulum Ca(2+)-release channel as did intact annexin VI.

Crystallization and preliminary X-ray studies of annexin IV (endonexin), a calcium-dependent phospholipid-binding protein

Annexin IV (endonexin) has been purified from chicken liver and crystallized by the vapour diffusion method. Crystals which diffract to at least 2.2 A have been obtained. They belong to space group R3 and have unit cell dimensions of a = b = 99.4 A, c = 96.2 A, alpha = 90 degrees, beta = 90 degrees, gamma = 120 degrees. There is one molecule of 32,500 Da per asymmetric unit.

Differential subcellular distribution of p36 (the heavy chain of calpactin I) and other annexins in the adrenal medulla

The annexins are a group of highly related Ca2(+)-dependent membrane-binding proteins that are present in a wide variety of cells and tissues. We have examined the subcellular distribution of five members of the annexin family in the adrenal medulla. Bovine adrenal medullary tissue was homogenized in buffers containing EGTA and fractionated on sucrose gradients. p36 (the large subunit of calpactin I) was found to be predominantly membrane associated, with approximately 20% present in fractions enriched in chromaffin granules. In contrast, lipocortin I was localized primarily to the cytosol, with only a small proportion found in plasma membrane-containing fractions. Like lipocortin I, endonexin I was found to be present almost entirely in the soluble fractions. The 67-kDa calelectrin was localized primarily to the plasma membrane fractions, with a small amount present in the chromaffin granule and cytoplasmic fractions. Synexin was present in both membranous and cytoplasmic fractions. p36 appeared to be a peripherally associated granule membrane protein in that it was dissociated from the membrane by addition of base and it partitioned with the aqueous phase when granule membranes were treated with Triton X-114. Antiserum against p10 (the small subunit of calpactin I) reacted with a protein of 19 kDa that is specifically localized in chromaffin granule membrane fractions. The differences in subcellular distributions of the annexins suggest that these proteins have distinct cellular functions. The finding that p36 is associated with chromaffin granule and plasma membrane fractions provides further support for a possible role of calpactin in exocytosis.

Lung calcium-dependent phospholipid-binding proteins: structure and function

Distinct peptide maps of two rabbit lung Ca2(+)-dependent phospholipid-binding proteins (PLBPs), 36,000 and 33,000, were generated by cyanogen bromide (CNBr) cleavage, trypsin or Staphylococcus aureus V8 proteinase digestion. The amino acid sequence of a CNBr-cleaved peptide of the 36,000 PLBP was aligned to the amino terminus of human lipocortin I with more than 77% identity, but had no identity with the known amino terminal sequence of other known annexins. Partial amino acid sequence of a 33,000 PLBP peptide demonstrated a close (56%) relationship to endonexin II, human placental anticoagulant protein, and porcine intestine protein II, but shared only 32% identity with lipocortin I, 30% with lipocortin II. Antiserum generated against purified 36,000 PLBP reacted strongly with the 33,000 PLBP, but did not react with any other rabbit lung cytosolic proteins. Both PLBPs inhibited the phospholipase A2 reaction when dioleoyl phosphatidylcholine and phosphatidylglycerol vesicles or monolayers were used as substrates. In the vesicle assay, the phospholipase A2 reaction was inhibited at lower substrate phospholipid concentrations but not at nearly saturating substrate concentrations. In the monolayer assay, the phospholipid-binding proteins did not inhibit phospholipase A2 at a low phospholipid surface concentration of 3.8.10(-3) molecules/A2, but they did at higher surface concentrations between 1.1 x 10(-2) and 3.8 x 10(-2) molecules/A2. The inhibition of phospholipase A2 by rabbit lung phospholipid-binding proteins is most likely due to the prevention of penetration by phospholipase A2 into the interface, a requirement for the enzyme to act on the substrate.

Crystallization and preliminary X-ray crystallographic studies of human placental annexin IV

Human placental annexin IV, a member of the annexin family of calcium and phospholipid-binding proteins, has been crystallized by the vapour diffusion method in the presence of calcium, using polyethylene glycol 8000. The crystals are orthorhombic, space C222(1), cell dimensions a = 105.4 A, b = 115.7 A, c = 80.7 A and diffract to at least 2.5 A resolution on a synchrotron source.

Characterization of the human lipocortin-2-encoding multigene family: its structure suggests the existence of a short amino acid unit undergoing duplication

Human genomic clones of the gene encoding lipocortin (LIP) 2 (p36) and of three pseudogenes have been isolated and characterized. The LIP2 gene is at least 40 kb long and consists of 13 exons. The three pseudogenes present typical features of retroposons and, together with the gene, probably represent the entire LIP2 multigene family. Chromosomal assignment of the four loci is proposed. The hypothesis that an ancestral unit coding for 15 to 20 amino acids may have been involved in the evolution of the gene is discussed.

Annexin-chromaffin granule membrane interactions: a comparative study of synexin, p32 and p67

The chromaffin granule membrane binding and aggregating properties of three annexins, synexin, p32 and p67, have been studied and compared. Each protein was activated to bind and aggregate membranes with a biphasic Ca2+ dependence, with one phase titrating between pCa 5.0-3.5 and the second at higher levels of calcium (pCa less than 3.5). cis-Unsaturated free fatty acids lowered these Ca2+ requirements by approximately one log unit. Barium and strontium were able to partially substitute for calcium, with the order of sensitivity Ca2+ greater than Sr2+ greater than Ba2+. The proteins appeared to bind to distinct but overlapping populations of receptor sites, and did so in a manner displaying positive cooperativity at the higher Ca2+ levels. The maximal efficacy of the proteins as membrane aggregators differed with synexin being 1-2-fold more efficacious than p32, which in turn was 7-fold more efficacious than p67. In combination, p67 was an effective inhibitor of granule aggregation induced by synexin or p32, while p32 was able to both promote and inhibit synexin-induced granule aggregation in a manner which varied with synexin concentration. The complexity of these annexin-membrane interactions may be a reflection of the multidomain structure of the annexins and may have implications for the differential functions of these proteins in cells.

Collagen-binding proteins of mammary epithelial cells are related to Ca2(+)- and phospholipid-binding annexins

Three major proteins of 34, 36, and 38 kDa were isolated from membrane preparations of chemically induced mammary tumors of the rat by collagen type I affinity chromatography and therefore were termed collagen-binding proteins (CBP). Three proteins in the same molecular weight range isolated from cell extracts by precipitation with calcium, solubilization of the precipitate with EGTA, and chromatography on hydroxylapatite were demonstrated to be immunologically related to CBP. As shown by immunoblot analysis, an antiserum directed against the cluster of the 34-38 kDa proteins reacted strongly with porcine intestinal protein I, weakly with porcine lipocortin I, and very weakly with porcine intestinal protein II. Antiserum against the 34 kDa protein reacted weakly with protein I but strongly with protein II. All three CBP reacted with protein I/calpactin I-specific antiserum of immunoblots and in immunoprecipitation experiments. However, antisera directed against CBP failed to show cross-reaction with collagen-binding protein anchorin II from chicken chondrocytes. Conversely, antisera against anchorin II did not react with CBP. Antiserum AS/87 immunoprecipitated CBP of 38 kDa that was labeled in a lactoperoxydase-catalyzed iodination, suggesting that this polypeptide is associated with the cell surface. Further, all three CBP were found to be phosphorylated by incubating mammary cells with 32P-orthophosphate. CBP bound to epithelial cell membranes in a Ca2+ dependent manner (= Triton X 100 insoluble form). Fractionated extraction and immunofluorescence microscopy also show that another form of CBP (= Triton X 100 soluble form) exists in these cells and is associated with a granular fraction. We therefore conclude that mammary collagen-binding proteins represent members of a family of Ca2(+)-binding membrane proteins. The 38 kDa CBP seems closely related to the pp60src kinase substrate protein I/calpactin I monomer, the 34 kDa CBP seems to be related or equivalent to protein II, while the relationship of the 36 kDa CBP to other defined proteins is still unclear.

Spin labeling of calcium-dependent phospholipid-binding proteins

Bovine lung annexins p32 and p34 were spin labeled with an iodoacetamidoproxyl spin label, a reagent that reportedly couples with protein methionine residues. Labeling conditions and stoichiometry were studied with the radiolabeled analogue [1-14C]iodoacetamide. As judged by this method, carboxamidomethylation of both p32 and p34 occurred up to a 0.7 mol ratio after 60 h of reaction at 37 degrees C and at pH 4. The two proteins retained Ca2(+)-dependent phospholipid-binding ability both in radiolabeled and in spin-labeled forms. Electron resonance spectra of spin-labeled p32 and p34 showed the features of a partially immobilized spin probe, with rotational correlation time values of 1.15 and 1.25 ns, respectively, which definitely indicate successful spin labeling. Quantitation of ESR spectra by computer double integration indicated 70% spin labeling of both proteins, as anticipated by radiolabeling. The use of spin-labeled p32 and p34 in the study of Ca2(+)-dependent interaction of annexins with biomembranes is proposed.

Protein kinase C inhibitor proteins. Purification from sheep brain and sequence similarity to lipocortins and 14-3-3 protein

Potent inhibitors of protein kinase C have been isolated from sheep brain by DEAE-cellulose, phenyl-Sepharose CL-4B and Mono Q anion-exchange chromatography. Analysis by one- and two-dimensional SDS/polyacrylamide gel electrophoresis showed the purified preparation to contain three bands ranging over 29-33 kDa in molecular mass, each consisting of several charge isomers with similar pI values (5.4-5.7). Peptide mapping, amino acid analysis and sequencing suggested that the proteins are related, with the possibility that some species are distinct gene products. The concentration of inhibitor proteins required for half-maximal inhibition of protein kinase C activity is 1.7 microM. Inhibitory activity could not be affected by increasing the substrate, cofactor or ATP concentration in the standard protein kinase C assay, but was abolished by heat treatment. The inhibitor preparation did not affect the binding of phorbol dibutyrate to protein kinase C and could inhibit phosphorylation over a wide range of calcium concentrations. Inhibitory activity could be removed by immunoprecipitation of the purified inhibitor proteins with polyclonal antibodies raised against synthetic peptides, the sequences corresponding to those of peptide fragments obtained from protein digests. Amino acid sequence analysis of the inhibitors confirms they are novel proteins although similarities exist with a neuronal specific protein termed 14-3-3 and the carboxy terminus of the calcium-lipid binding series (endonexin/calpactin/lipocortin).