The crystal and molecular structure of human annexin V, an anticoagulant protein that binds to calcium and membranes

Human annexin V (PP4), a member of the family of calcium, membrane binding proteins, has been crystallized in the presence of calcium and analysed by crystallography by multiple isomorphic replacement at 3 A and preliminarily refined at 2.5 A resolution. The molecule has dimensions of 64 x 40 x 30 A3 and is folded into four domains of similar structure. Each domain consists of five alpha-helices wound into a right-handed superhelix yielding a globular structure of approximately 18 A diameter. The domains have hydrophobic cores whose amino acid sequences are conserved between the domains and within the annexin family of proteins. The four domains are folded into an almost planar array by tight (hydrophobic) pair-wise packing of domains II and III and I and IV to generate modules (II-III) and (I-IV), respectively. The assembly is symmetric with three parallel approximate diads relating II to III, I to IV and the module (II-III) to (I-IV), respectively. The latter diad marks a channel through the centre of the molecule coated with charged amino acid residues. The protein has structural features of channel forming membrane proteins and a polar surface characteristic of soluble proteins. It is a member of the third class of amphipathic proteins different from soluble and membrane proteins.

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.

The calcium binding sites in human annexin V by crystal structure analysis at 2.0 A resolution. Implications for membrane binding and calcium channel activity

Crystal structure analysis and refinement at 2.0 A resolution of a rhombohedral crystal form of human annexin V at high calcium concentration revealed a domain motion compared to the previously analysed hexagonal crystal form. Five calcium ions were located on the convex face of the molecule. Three strongly bound calciums are liganded at protruding interhelical loops and Asp or Glu residues in homologous positions in repeats I, II and IV. Five proteinaceous oxygens and one solvent molecule form the coordination polyhedron in each case. The unoccupied seventh site is suggested as the phospholipid headgroup binding site. Two more weakly bound sites were identified by lanthanum labelling. The structural features suggest that annexin V attaches with its convex face to membranes by specific calcium mediated interactions with at least three phospholipids. The adjacent membrane bilayer may thus become locally disordered and permeable to allow calcium inflow through the central polar channel of the molecule.

The crystal structure and ion channel activity of human annexin II, a peripheral membrane protein

Annexin II binds in a calcium-dependent manner to acidic phospholipids and is a substrate of some protein kinases. An N-terminally shortened form of human annexin II was crystallized and its molecular structure determined. It is very similar to two previously described members of this protein family, annexin I and annexin V. The protein structure is nearly completely alpha-helical organized as four compact domains which consist of five alpha-helices each. The domains surround a hydrophilic pore. The calcium binding sites are located at the convex side of the structure as in annexin V. Recombinant and natural porcine annexin II are active as ion channel with characteristics similar to annexin V, while N-terminally shortened annexin II and the heterotetramer (annexin II-p11)2 are inactive. Two cysteine residues, Cys133 and Cys262, form a disulphide bridge connecting domains II and III, adding further weight to the notion that ion channel activity does not require major structural rearrangements.

Antithrombin inhibits lipopolysaccharide-induced tissue factor and interleukin-6 production by mononuclear cells, human umbilical vein endothelial cells, and whole blood

OBJECTIVE

To investigate the effects of antithrombin on lipopolysaccharide (LPS)-induced tissue factor and interleukin-6 (IL-6) production in three different in vitro cellular systems: whole blood, human umbilical vein endothelial cells, and mononuclear cells.

DESIGN AND SETTING

Laboratory in vitro study of the effects of antithrombin on procoagulant activity and cytokine release by LPS-stimulated endothelial and peripheral blood cells.

SUBJECTS

In vitro whole blood, isolated human umbilical vein endothelial cell, and mononuclear cell cultures.

INTERVENTIONS

Addition of antithrombin to LPS-treated whole blood, human umbilical vein endothelial cells, and mononuclear cells.

MEASUREMENT AND MAIN RESULTS

Citrated whole blood, isolated human umbilical vein endothelial cells, or mononuclear cells were stimulated with LPS for 4-6 hrs in the presence or absence of antithrombin. Tissue factor activity was estimated by a tissue factor-dependent clotting or chromogenic assay and IL-6 was measured by specific ELISA. Antithrombin was found to inhibit tissue factor and IL-6 production in all three systems in a dose-dependent manner (0-40 IU/mL). Flow-through fractions of immunoadsorbed antithrombin concentrate were found to be ineffective. Five different batches of the same antithrombin concentrate were tested and the inhibitory activity was found to be consistent throughout all batches. Up to 40 microM of recombinant hirudin, a specific thrombin inhibitor, did not inhibit the production of tissue factor or IL-6 in either of the three cell systems, suggesting that the observed inhibition by antithrombin was not due solely to its ability to inhibit thrombin.

CONCLUSIONS

Apart from the inhibition of thrombin and other activated clotting factors, antithrombin may also down-regulate the cellular expression of proinflammatory cytokines. Consequently, antithrombin concentrates may have value in the treatment of sepsis-induced disseminated intravascular coagulation.

Cell-surface heparan sulfate proteoglycan-mediated regulation of human neutrophil migration by the serpin antithrombin III

The serpin antithrombin III (AT III) is reported to have hemostasis-regulating and anti-inflammatory properties. To determine its ability to influence thrombin-independent leukocyte responses, the direct effects of the AT III concentrate Kybernin P and a monoclonal antibody-purified AT III on neutrophil migration were studied. Chemotactic activity of human neutrophils isolated from the blood of healthy donors was determined in modified Boyden microchemotaxis chambers, and binding studies were performed according to standard experimental protocols. Preincubation in vitro of neutrophils with Kybernin P or immune-adsorbed AT III significantly deactivated migration toward fMet-Leu-Phe, or interleukin-8 (IL-8), in a concentration-dependent manner. In the absence of additional attractants, neutrophils exhibited a migratory response toward gradients of AT III preparations. True chemotaxis was confirmed in checkerboard assays. Analyses revealed that the AT III heparin-binding site interacts with neutrophil membrane-associated heparan sulfate proteoglycan receptors. Mechanisms of intracellular signaling differed; the deactivation of IL-8-induced chemotaxis resulted from tyrphostin-sensitive interactions of AT III-signaling with the IL-8 signal transduction pathway, whereas AT III-induced chemotaxis involved protein kinase C and phosphodiesterases. Signaling similarities between AT III and the proteoglycan syndecan-4 may suggest the binding of AT III to this novel type of membrane receptor. Under physiological conditions, AT III may prevent neutrophils from premature activation. Moreover, the systemic administration of AT III concentrate could have beneficial effects in combating systemic inflammation.

Factor VII and single-chain plasminogen activator-activating protease: activation and autoactivation of the proenzyme

Structural and biological characteristics of a recently described plasma serine protease, which displayed factor VII as well as pro-urokinase-activating properties in vitro, indicated a dual role for this factor VII-activating protease (FSAP) in hemostasis. Only the active protease (two-chain FSAP) has been isolated from plasma and from a prothrombin complex concentrate, whereas activators of the proenzyme have not been identified so far. After purification of the FSAP proenzyme from cryo-poor plasma by adsorption to an immobilized mAb and subsequent ion-exchange chromatography, activation to generate two-chain FSAP was followed by a direct chromogenic assay as well as by the ability of two-chain FSAP to activate pro-urokinase. Purified single-chain FSAP underwent autoactivation leading to the typical protease two-chain pattern and subsequent degradation products, as demonstrated by Western-blotting analysis using a site-specific mAb. This autoactivation was significantly enhanced in the presence of heparin, whereas Ca2+ ions stabilized single-chain FSAP (the proenzyme) resulting in slower autoactivation kinetics. Correspondingly, the heparin-augmented reaction, which was associated with autodegradation particularly of the protease domain, was slowed down by co-incubation with Ca2+. Of the other proteases and cofactors tested, only urokinase (uPA) was able to generate the typical two-chain FSAP pattern. Studies with different forms of uPA suggest that the catalytic activity of pro-urokinase/uPA is needed to activate single-chain FSAP, indicating that it is the only hemostatic protease that can act as a physiological activator of FSAP.

In-vivo antithrombotic potency of placenta protein 4 (annexin V)

The antithrombotic properties of Placenta Protein 4 (PP4) were investigated in laser or photochemically induced thrombus formation models in rats. In both in-vivo test-systems PP4 displayed a significant antithrombotic effect at dose levels as low as 0.3 and 1.0 mg/kg body weight. Bleeding times, surprisingly, were not prolonged significantly at these dose regimens. Maximal inhibition of thrombus formation in the laser-model was observed 15 min after intravenous administration of PP4, but was not recognizable in a clear-cut reaction in the second model. Determination of PP4 plasma levels in two monkeys revealed a half-life of 11.5 and 14.9 min, respectively. The maximal anticoagulant effect was observed between 15 and 30 min after administration of PP4 as determined functionally by means of thrombelastography.

The anti-inflammatory actions of antithrombin--a review

Leukocyte-endothelial cell interaction and microvascular perfusion failure are characteristic deteriorations of the microcirculation in endotoxaemia and are known to play a crucial role in the development of septic multiple organ dysfunction. Recent studies have indicated that antithrombin III treatment is capable of significantly ameliorating these microcirculatory disorders. Endothelial cells have important anticoagulant systems, including the heparan sulfate-antithrombin system. Antithrombin III stimulates prostacyclin generation in endothelial cells by interacting with heparan sulfate of endothelial cells and inhibits cytokine and tissue factor production in endothelial cells and monocytes. Similar mechanisms may be involved in cellular actions of antithrombin III causing desensitization of chemoattractant receptors of leukocytes by activating the heparan sulfate proteoglycan, syndecan-4. Thus, antithrombin III might be among the useful agents for treating coagulation abnormalities associated with sepsis or other inflammation because it inhibits not only coagulation but also downregulation of anticoagulant activities of endothelial cells and affects leukocyte activation.

Anticoagulant properties of placenta protein 4 (annexin V)

A placenta protein, originally termed PP4, was found to inhibit the aPTT in a concentration-dependent manner. PP4 which turned out to be identical with a vascular anticoagulant of the annexin type, inhibits the blood clotting process by binding of the essential lipids in a reaction which is dependent on calcium ions. Also in the presence of calcium PP4 combines with platelet membranes neutralizing their procoagulant effect. By fluorescence-microscopy binding of PP4 to stimulated macrophages is shown. The antithrombotic effect of PP4 is demonstrated by means of thrombelastography of human blood. Coagulation triggered by the addition of thromboplastin/lipid-mixtures is extinguished by PP4.

The primary structure of cytochrome c1 from Neurospora crassa

The primary structure of the cytochrome c1 subunit of ubiquinol-cytochrome-c reductase from mitochondria of Neurospora crassa was determined by sequencing the cDNA of a bank cloned in Escherichia coli. From the coding region the sequence of 332 amino acids, corresponding to the molecular mass of 36,496 Da, was derived for the precursor protein. The mature protein, the N terminus of which was previously sequenced [Tsugita et al. (1979) in Cytochrome oxidase (King, T. E. et al., eds) pp. 67-77, Elsevier, New York], consists of 262 amino acids and has the molecular mass of 29,908 Da including the heme. The sequence contains an N-terminal hydrophilic part of 211 residues, which carries the heme, a hydrophobic stretch of 15 residues, which is assumed to anchor the protein to the membrane, and a C-terminal hydrophilic part of 36 residues. The N-terminal presequence of 70 amino acids contains 9 positive charges but only 1 negative charge and is characterized by a stretch of 20 uncharged residues.

Quantitation of the factor VII- and single-chain plasminogen activator-activating protease in plasmas of healthy subjects

Plasma samples of 189 healthy subjects were investigated for antigen levels of the recently reported factor VII- and single-chain plasminogen activator-activating protease (FSAP) and the corresponding pro-urokinase activating potencies. While the age of donors had no significant effect on the investigated parameters, female plasmas revealed a trend to higher antigen contents and activity levels. Surprisingly, as much as 9% of all samples contained significantly reduced single-chain urinary plasminogen activator activating potential, whereas antigen concentrations were normal. Additionally, 1% of the plasmas was found to decrease in both FSAP antigen and activity contents. FSAP of three subjects displaying reduced activities throughout a follow-up period of 6 months were purified from plasmas and were characterized. As compared with pool plasma derived FSAP, investigation of the individual preparations confirmed their reduced potency to activate pro-urokinase. However, factor VII activation was not affected. It is speculated that the FSAP binding site for single-chain plasminogen activators is affected, potentially by as yet unknown polymorphism(s) or mutation(s).

The FVII activating protease cleaves single-chain plasminogen activators

A serine protease isolated from plasma sharing structural characteristics with a hepatocyte growth factor activator-like protease has been demonstrated recently to activate FVII. Accordingly, it was named 'FVII activator'. Until now an impact of this protease on the fibrinolytic system has not been reported. We islolated the protease from cryo-poor plasma by subsequent ion exchange chromatography and adsorption to immobilized heparin and/or aprotinin. Incubation of single-chain plasminogen activators (sc-PAs) with the FVII activator revealed significant activation of urokinase sc-PA (scu-PA) and tissue sc-PA (sct-PA) in vitro. It was enhanced in the presence of calcium and heparin. Compared to kallikrein, a more efficient activation of scu-PA was observed, whereas sct-PA appeared to be a poorer substrate for the FVI activator. At low protease concentrations and in the presence of heparin the scu-PA activation was comparable to plasmin. Employing recalcified whole blood thrombelastography, the lysis of initially formed fibrin was observed after addition of a combination of scu-PA and the FVII activator, whereas the scu-PA alone had a negligible effect at the concentration used. The study results as presented demonstrate that the FVII activator is a potent activator of sc-PAs in vitro. Whether it plays a physiological role in fibrinolysis deserves further investigation. Its comparatively high affinity to heparin assumes a function in cell surface or matrix events.

Purification and characterization of six annexins from human placenta

Isolation of six calcium-binding proteins from human placenta is described by means of hydrophobic chromatography, calcium-dependent adsorption to heparin-Sepharose and ion-exchange chromatography. These proteins were characterized and identified as PP4, PP4-X, PAP III, p68 and lipocortins I and II belonging to the family of annexins. Antibodies raised against PP4, PAP III and p68 revealed to be highly specific, while those raised against PP4-X reacted with all investigated annexins, except PP4. Cross-reactivity was also observed between lipocortins I and II. All annexins inhibited in a concentration-dependent manner blood coagulation but with different potencies as was determined by means of a modified thromboplastin time test. The most potent inhibitors turned out to be PP4 and PAP III, followed by PP4-X, lipocortin I, p68 and lipocortin II.

Characterisation of a novel high-purity, double virus inactivated von Willebrand Factor and Factor VIII concentrate (Wilate)

This study summarises the biochemical and functional properties of a new generation plasma-derived, double virus inactivated von Willebrand Factor/Factor VIII (VWF/FVIII) concentrate, Wilate, targeted for the treatment of both von Willebrand disease (VWD) and haemophilia A. The manufacturing process comprises two chromatographic steps based on different performance principles, ensuring a high purity of the concentrate (mean specific activity in 15 consecutive production batches: 122 IU FVIII:C/mg total protein) and, thus, minimising the administered protein load to the patient (specification: < or = 15 mg total protein per 900 IU Wilate). The optimised solvent/detergent (S/D) treatment and prolonged terminal dry-heat (PermaHeat) treatment of the lyophilised product at a specified residual moisture (RM) provide two mechanistically independent, effective and robust virus inactivation procedures for enveloped viruses and one step for non-enveloped viruses. These process steps are aggressive enough to inactivate viruses efficiently, but yet gentle enough to maintain the structural integrity and function of the VWF and FVIII molecules, as proven by state-of-the-art assays covering the diverse features of importance. The VWF multimeric pattern is close to the one displayed by normal plasma, with a consistent content of more than 10 multimers, but a relatively lower portion of the very high multimers. The multimeric triplet structure is normal, underlining the gentle and effective manufacturing process, which does not require the addition of protein stabilisers at any step. The balanced activity ratio of VWF to FVIII is close to that of plasma from healthy subjects, rendering Wilate suitable also for the safe and effective treatment of patients with VWD.

Improved performance characteristics of the von Willebrand factor ristocetin cofactor activity assay using a novel automated assay protocol

BACKGROUND, OBJECTIVES AND METHODS: An accurate, sensitive and precise assay for reliable determination of the ristocetin cofactor activity of von Willebrand factor (VWF:RCo) in plasma and von Willebrand Factor (VWF)-containing concentrates has been evaluated. The assay is based on a commercially available automated protocol with modifications including a combination of adding additional ristocetin and the use of two calibration curves for the high and low measuring ranges.

RESULTS

 Addition of extra ristocetin resulted in improved measurement of VWF recoveries from various VWF-containing concentrates that were underestimated using the standard automated protocol. The modifications resulted in improved assay performance over an extended measuring range (2.00-0.03 IUmL(-1) ). Accuracy was tested using VWF deficiency plasma spiked with the 1st international standard (IS) for VWF concentrate. Seven dilutions, ranging from 1.80 to 0.05IUmL(-1) , were analyzed and resulted in measured concentrations between 80% and 100% of the assigned potency of the standard. Linearity was determined from the regression plot of the same concentrate dilutions and resulted in a correlation coefficient of 0.998. The repeatability, expressed as coefficient of variation, was 2% in the normal range (0.90IUmL(-1) ) and 8% at the level of 0.05IUmL(-1) . The corresponding reproducibility results were 2% and 15% at the normal and low measuring ranges, respectively.

CONCLUSIONS

 Analysis of patients with von Willebrand disease (VWD) indicates that the modified automated BCS(®) protocol has a superior discrimination power compared with the standard protocol. This is especially true in samples with low VWF, as in patients with type 3 VWD.

Normal levels of ADAMTS13 and factor H are present in the pharmaceutically licensed plasma for transfusion (Octaplas®) and in the universally applicable plasma (Uniplas) in development

BACKGROUND AND OBJECTIVES

The pathomechanism of thrombotic thrombocytopenic purpura (TTP) and atypical haemolytic uraemic syndrome (aHUS) is associated with a severe deficiency of ADAMTS13 and factor H. The aim of this study was to quantify the levels of ADAMTS13 and factor H in the pharmaceutically licensed plasma for transfusion, Octaplas, and the universally applicable plasma, Uniplas (development product, working title). Furthermore, Octaplas batches of blood groups A, B, O, AB, and plasmas derived from different sources were compared.

MATERIALS AND METHODS

Twenty-four Octaplas and three Uniplas batches were selected for the study. ADAMTS13 activities were measured by fluorescence resonance energy transfer assay, ADAMTS13 antigen levels were quantified using enzyme-linked immunosorbent assay test kit, while factor H antigen levels were detected using radial immunodiffusion (RID) methods. In addition, von Willebrand factor (vWF) multimeric analyses were performed.

RESULTS

Both Octaplas, produced from US and European plasma of different blood groups, and Uniplas contain ADAMTS13 antigen and activity levels as well as factor H concentrations at normal levels without significant differences. In addition, Octaplas and Uniplas show a vWF multimeric pattern comparable to normal plasma.

CONCLUSION

The study revealed that Octaplas and Uniplas contain normal levels of ADAMTS13 at low batch-to-batch variations. Therefore, both products can substitute the missing or neutralized protease activity in TTP patients and thereby limit vWF-dependent (platelet-related) thrombosis. In addition, both plasma products contain factor H at a physiological level, and, thus can be used efficiently in the treatment of aHUS patients, which have been shown to benefit from plasma administration.

Comparative study on the in vitro effectiveness of antithrombotic agents

The synthetic low molecular weight inhibitors MD 805, FUT-175 and FOY as well as heparin and r-Hirudin were compared for their in vitro antithrombotic potencies and protease specificities. The amidolytic activity of thrombin and the plasma coagulation were effectively inhibited by MD 805 and, in particular, by r-Hirudin. FUT-175 and FOY revealed only weak inhibition. None of the synthetic substances discriminated between alpha-, beta- and gamma-thrombin. Beside r-Hirudin only MD 805 revealed a relatively good specificity for thrombin. On the contrary, FUT-175 and FOY are unspecific and can not be classified as thrombin inhibitors.

Inhibition of human skin phospholipase A2 by "lipocortins" is an indirect effect of substrate/lipocortin interaction

Proteins of the annexin/lipocortin family have been claimed to mediate the anti-inflammatory action of glucocorticosteroids by the inhibition of phospholipases A2. This hypothesis has been challenged by the finding that annexins do not directly interact with the enzyme in a classical enzyme/inhibitor behavior, but more likely block the access of the phospholipase A2 to its substrate by binding to phospholipids. Because former studies with skin phospholipase A2 suggested a specific regulation by annexin-1, we investigated the substrate dependence of this effect. For this purpose phospholipase A2 activities in human epidermis and dermis homogenates were measured in the presence of various amounts of annexins-1, -2, or -5. The respective annexin was preincubated in separate series either with the substrate or with the enzyme. We found a partial inhibition of both epidermal and dermal phospholipase A2 activities with all annexins tested (annexin-5 >> annexin-2 > annexin-1). The inhibitory effect was absolutely dependent on the annexin/phospholipid ratio and occurred only at very high annexin concentrations relative to the amount of substrate. Our data demonstrate that the inhibition of human skin phospholipase A2 by annexins depends on the substrate concentrations, as has been shown for phospholipases A2 of other origins as well. All observations can be explained by the current "substrate depletion model" characterizing the indirect effects of annexins on phospholipase A2 activities. It is therefore rather unlikely that annexins are directly involved in the regulation of phospholipase A2 activity of human skin under physiologic conditions.

Localization of annexins in normal and diseased human skin

Annexins (AX) or lipocortins are a family of calcium and phospholipid binding proteins that have been implicated to play a role in the regulation of inflammation and cellular differentiation. To investigate a potential role of AX in skin disorders we studied the distribution of six different AX in normal human skin (NHS) and several inflammatory and hyperproliferative skin diseases. A distinct staining pattern could only be shown for AX-1 and AX-2. In NHS AX-1-antibody (Ab) displayed a very strong reactivity with eccrine sweat ducts. In the diseases investigated we found a highly increased expression of AX-1 in keratinocytes (KCs) in the vicinity of inflammatory processes such as psoriasis. Furthermore, the AX-1 expression was increased in differentiated squamous cell carcinoma (SCC) whereas undifferentiated SCC and basal cell carcinoma were negative. AX-3, -4, -5, and -6 showed no distinctive expression pattern. Our data demonstrate an abnormal distribution of AX-1 in association with proliferating KCs under inflammatory and neoplastic conditions. Its pattern of reactivity shows similarities to the known distribution of the EGF-receptor kinase, which has been demonstrated to phosphorylate AX-1 with high activity in various cellular systems. These results support the concept that the appearance of AX-1 is linked to a certain level of KC differentiation.

Cloning and expression of a cDNA encoding human placental protein 11, a putative serine protease with diagnostic significance as a tumor marker

The placental protein 11 (PP11) can act as a tumor marker because of its specific association with various forms of cancer. A lambda gt11 cDNA library prepared from human placenta was screened with a polyclonal anti-PP11 antiserum. Out of 10(6) independent clones, only one clone reacted with the anti-PP11 antiserum. The isolated cDNA coded only for the carboxy-terminal part of PP11 and was subsequently used to rescreen a lambda gt10 placental cDNA library. Two cDNA clones out of 10(6) screened were identified encoding the entire protein of 369 amino acids, including a typical hydrophobic signal sequence of 18 amino acids. Expression of the PP11 cDNA coding sequence in Escherichia coli resulted in the synthesis of a protein with the expected size which can be specifically immunoprecipitated with anti-PP11 antiserum. Fractionation experiments revealed that two forms of the protein are present in the bacterial cell: a higher-molecular-weight form of approximately 42 kD in the cytoplasm and a smaller-molecular-weight form of approximately 42 kD in the periplasm. This result indicates that PP11 can be synthesized in E. coli and is process by removal of the hydrophobic signal sequence. Both the placental and the processed recombinant PP11 protein exhibit a protease activity.

Annexin proteins PP4 and PP4-X. Comparative characterization of biological activities of placental and recombinant proteins

The human placental proteins PP4 and PP4-X, belonging to the annexin protein family, were expressed in Escherichia coli at high yield. The proteins were purified to homogeneity. The physicochemical parameters of the recombinant proteins were determined and compared with those of their natural placental counterparts. Except for a minor change in the pI, the proteins appeared to be indistinguishable by several criteria. Both recombinant PP4 and recombinant PP4-X were biologically active in a thromboplastin inhibition test and in a phospholipase A2 inhibition test.