Biomedical subjects

P García de Frutos

Publications and source records attributed to P García de Frutos.

At least 19 recordsLinked to original sources

PubMed2000

The first laminin G-type domain in the SHBG-like region of protein S contains residues essential for activation of the receptor tyrosine kinase sky.

Vitamin K-dependent protein S and the product of growth-arrest-specific gene 6 (Gas6) both possess the ability to phosphorylate members of the Axl/Sky subfamily of receptor tyrosine kinases. However, Gas6 appears to be the bona fide ligand for these receptors in man, as human protein S has been demonstrated to activate murine Sky but not the human orthologue. In contrast, bovine protein S is able to stimulate human Sky despite its high degree of sequence identity with human protein S. The domain organisations of protein S and Gas6 are virtually identical and the C-terminal SHBG-like region, containing two globular (G) domains, has been shown to play a crucial role in the receptor stimulation. In order to further localise the area responsible for the interaction, a number of protein chimeras were used to stimulate human Sky. Each chimera had one part of the human protein S SHBG-like region replaced by the corresponding part of bovine protein S or human Gas6. We found that human protein S may indeed activate human Sky but only above physiological plasma concentrations. The human-bovine protein S chimeras provided new information implying that the first G domain contains critical residues for the interaction with the Sky receptor. Moreover, these residues do not seem to be clustered but rather to be distributed at various positions in the first G domain.

Animals↗

PubMed2000

The second laminin G-type domain of protein S is indispensable for expression of full cofactor activity in activated protein C-catalysed inactivation of factor Va and factor VIIIa.

Vitamin K-dependent protein S is a cofactor to the anticoagulant serine protease activated protein C (APC) in the proteolytic inactivation of the procoagulant, activated factor V (FVa) and factor VIII (FVIIIa). In the FVa degradation, protein S selectively accelerates the cleavage at Arg306, having no effect on the Arg506 cleavage. In the FVIIIa inactivation, the APC-cofactor activity of protein S is synergistically potentiated by FV, which thus has the capacity to function both as a pro- and an anticoagulant protein. The SHBG-like region of protein S, containing two laminin G-type domains, is required for the combined action of protein S and FV. To elucidate whether both G domains in protein S are needed for expression of APC-cofactor activities, chimeras of human protein S were created in which the individual G domains were replaced by the corresponding domain of the homologous Gas6, which in itself has no anticoagulant activity. In a plasma-based assay, chimera I (G1 from Gas6) was as efficient as wild-type recombinant protein S, whereas chimera II (G2 from Gas6) was less effective. The synergistic cofactor activity with FV in the inactivation of FVIIIa was lost by the replacement of the G2 domain in protein S (chimera II). However, chimera I did not exert full APC-cofactor activity in the FVIIa degradation, indicating involvement of both G domains or the entire SHBG-like region in this reaction. Chimera I was fully active in the degradation of FVa in contrast to chimera II, which exhibited reduced cofactor activity compared to protein S. In conclusion, by using protein S-Gas6 chimeric proteins, we have identified the G2 domain of protein S to be indispensable for an efficient inactivation of both FVIIa and FVa, whereas the G1 domain was found not to be of direct importance in the FVa-inactivation experiments.

Anticoagulants↗

PubMed2000

Protein S Thr103Asn mutation associated with type II deficiency reproduced in vitro and functionally characterised.

Protein S functions as a cofactor to activated protein C (APC) in the degradation of FVa and FVIIIa. In protein S, the thrombin sensitive region (TSR) and the first EGF-like domain are important for expression of the APC cofactor activity. A naturally occurring Thr103Asn (T103N) mutation in the first EGF-like domain of protein S has been associated with functional (type II) protein S deficiency. To elucidate the functional consequences of the T103N mutation, recombinant protein S mutant was expressed in mammalian cells and functionally characterised. The expression level of protein S T103N from transiently transfected COS 1 cells was equal to that of wild type protein S. The mutant protein S and wild type protein S were also expressed in 293 cells after stable transfection, and the recombinant proteins purified. In APTT- and PT-based coagulation assays, the mutant protein demonstrated approximately 50% lower anticoagulant activity as compared to wild type protein S. The functional defect was further investigated in FVa- and FVIIIa-degradation assays. The functional defect of mutant protein S was attenuated at increasing concentrations of APC. The results demonstrate the region around residue 103 of protein S to be of functional importance, possibly through a direct interaction with APC.

Amino Acid Substitution↗

PubMed1999

Thrombophilia as a multigenic disease.

BACKGROUND AND OBJECTIVE: Venous thrombosis is a common disease annually affecting 1 in 1000 individuals. The multifactorial nature of the disease is illustrated by the frequent identification of one or more predisposing genetic and/or environmental risk factors in thrombosis patients. Most of the genetic defects known today affect the function of the natural anticoagulant pathways and in particular the protein C system. This presentation focuses on the importance of the genetic factors in the pathogenesis of inherited thrombophilia with particular emphasis on those defects which affect the protein C system. INFORMATION SOURCES: Published results in articles covered by the Medline database have been integrated with our original studies in the field of thrombophilia. STATE OF THE ART AND PERSPECTIVES: The risk of venous thrombosis is increased when the hemostatic balance between pro- and anti-coagulant forces is shifted in favor of coagulation. When this is caused by an inherited defect, the resulting hypercoagulable state is a lifelong risk factor for thrombosis. Resistance to activated protein C (APC resistance) is the most common inherited hypercoagulable state found to be associated with venous thrombosis. It is caused by a single point mutation in the factor V (FV) gene, which predicts the substitution of Arg506 with a Gln. Arg506 is one of three APC-cleavage sites and the mutation results in the loss of this APC-cleavage site. The mutation is only found in Caucasians but the prevalence of the mutant FV allele (FV:Q506) varies between countries. It is found to be highly prevalent (up to 15%) in Scandinavian populations, in areas with high incidence of thrombosis. FV:Q506 is associated with a 5-10-fold increased risk of thrombosis and is found in 20-60% of Caucasian patients with thrombosis. The second most common inherited risk factor for thrombosis is a point mutation (G20210A) in the 3' untranslated region of the prothrombin gene. This mutation is present in approximately 2% of healthy individuals and in 6-7% of thrombosis patients, suggesting it to be a mild risk factor of thrombosis. Other less common genetic risk factors for thrombosis are the deficiencies of natural anticoagulant proteins such as antithrombin, protein C or protein S. Such defects are present in less than 1% of healthy individuals and together they account for 5-10% of genetic defects found in patients with venous thrombosis. Owing to the high prevalence of inherited APC resistance (FV:Q506) and of the G20210A mutation in the prothrombin gene, combinations of genetic defects are relatively common in the general population. As each genetic defect is an independent risk factor for thrombosis, individuals with multiple defects have a highly increased risk of thrombosis. As a consequence, multiple defects are often found in patients with thrombosis.

3' Untranslated Regions↗

PubMed1998

The SHBG-like region of protein S is crucial for factor V-dependent APC-cofactor function.

Activated protein C (APC) regulates blood coagulation by degrading factor Va (FVa) and factor VIIIa (FVIIIa). Protein S is a cofactor to APC in the FVa degradation, whereas FVIIIa degradation is potentiated by the synergistic APC-cofactor activity of protein S and factor V (FV). To elucidate the importance of the sex-hormone-binding globulin (SHBG)-like region in protein S for expression of anticoagulant activity, a recombinant protein S/Gas6 chimera was constructed. It comprised the amino-terminal half of protein S and the SHBG-like region of Gas6, a structurally similar protein having no known anticoagulant properties. The protein S/Gas6 chimera expressed 40-50%, APC-cofactor activity in plasma as compared to wild-type protein S. In the degradation of FVa by APC, the protein S/Gas6 chimera was only slightly less efficient than wild-type protein S. In contrast, the protein S/Gas6 chimera expressed no FV-dependent APC-cofactor activity in a FVIIIa-degradation system. This demonstrates the SHBG-like region to be important for expression of APC-cofactor activity of protein S and suggests that the SHBG-like region of protein S interacts with FV during the APC-mediated inactivation of FVIIIa.

Factor V↗

PubMed1998

Structural investigation of C4b-binding protein by molecular modeling: localization of putative binding sites.

C4b-binding protein (C4BP) contributes to the regulation of the classical pathway of the complement system and plays an important role in blood coagulation. The main human C4BP isoform is composed of one beta-chain and seven alpha-chains essentially built from three and eight complement control protein (CCP) modules, respectively, followed by a nonrepeat carboxy-terminal region involved in polymerization of the chains. C4BP is known to interact with heparin, C4b, complement factor I, serum amyloid P component, streptococcal Arp and Sir proteins, and factor VIII/VIIIa via its alpha-chains and with protein S through its beta-chain. The principal aim of the present study was to localize regions of C4BP involved in the interaction with C4b, Arp, and heparin. For this purpose, a computer model of the 8 CCP modules of C4BP alpha-chain was constructed, taking into account data from previous electron microscopy (EM) studies. This structure was investigated in the context of known and/or new experimental data. Analysis of the alpha-chain model, together with monoclonal antibody studies and heparin binding experiments, suggests that a patch of positively charged residues, at the interface between the first and second CCP modules, plays an important role in the interaction between C4BP and C4b/Arp/Sir/heparin. Putative binding sites, secondary-structure prediction for the central core, and an overall reevaluation of the size of the C4BP molecule are also presented. An understanding of these intermolecular interactions should contribute to the rational design of potential therapeutic agents aiming at interfering specifically some of these protein-protein interactions.

Amino Acid Sequence↗

PubMed1998

Clarification of the risk for venous thrombosis associated with hereditary protein S deficiency by investigation of a large kindred with a characterized gene defect.

BACKGROUND: Protein S is an important regulatory protein of the coagulation cascade. The risk for venous thrombosis associated with protein S deficiency has been uncertain because all previous risk estimates used phenotypic evaluation alone, which can be ambiguous. OBJECTIVE: To quantitate the risk for thrombosis associated with a characterized protein S gene mutation that causes a Gly295-->Val substitution and protein S deficiency. DESIGN: Retrospective study of a single extended family. SETTING: University hospital referral center. PARTICIPANTS: A 122-member protein S-deficient family, in which 44 members had a recently characterized gene defect. MEASUREMENTS: Comprehensive history of thrombosis, history of exposure to acquired risk factors for thrombosis, levels of total and free protein S antigen, and genotype for the mutation causing the Gly295-->Val substitution. RESULTS: Kaplan-Meier analysis of thrombosis-free survival showed that the probability of remaining free of thrombosis at 30 years of age is 0.5 (95% CI, 0.33 to 0.66) for carriers of the Gly295-->Val mutation compared with 0.97 (CI, 0.93 to 1.0) for normal family members (P < 0.001). In a multivariate Cox regression model that included smoking and obesity, the mutation was a strong independent risk factor for thrombosis (hazard ratio, 11.5 [CI, 4.33 to 30.6]; P < 0.001). For free (but not total) protein S antigen levels, the distributions of persons with and persons without the mutation did not overlap. CONCLUSIONS: Protein S deficiency, as defined by the presence of a causative gene mutation or a reduced level of free protein S antigen, is a strong independent risk factor for venous thrombosis in a clinical affected family.

Adolescent↗

PubMed1998

A common 4G allele in the promoter of the plasminogen activator inhibitor-1 (PAI-1) gene as a risk factor for pulmonary embolism and arterial thrombosis in hereditary protein S deficiency.

Reduced fibrinolytic capacity due to increased plasminogen activator inhibitor-1 (PAI-1) activity in plasma is a common finding in patients with coronary heart disease or venous thromboembolism, although its clinical significance is debated. Recently, a dimorphism in the PAI-1 promoter (4G-5G) has been reported and homozygosity for the 4G allele is associated with increased transcription and higher PAI-1 levels. Homozygous 4G genotype has been suggested to be a risk factor for myocardial infarction. In the present study, the 4G-5G dimorphism was determined in 349 individuals from 21 thrombophilic families with hereditary protein S deficiency and in 140 unrelated healthy controls. Among the 143 protein S deficient individuals, there was no relationship between deep or superficial venous thrombosis and the PAI-1 dimorphism. However, 26% (12/46) of individuals having protein S deficiency combined with homozygosity for the 4G allele had suffered pulmonary embolism as compared to 7% (7/97) of protein S deficient individuals carrying at least one 5G allele (p = 0.0019). In protein S deficient individuals, arterial thrombosis was found to be associated with smoking and 4G homozygosity. No association was found between the PAI-1 dimorphism and arterial or venous thromboembolism in family members without protein S deficiency. In conclusion, the PAI-1 genotype affects the phenotypic expression of thrombophilia in protein S deficient individuals.

Adolescent↗

PubMed1997

Stimulation of Sky tyrosine phosphorylation by bovine protein S--domains involved in the receptor-ligand interaction.

Protein S is an anticoagulant vitamin-K-dependent plasma glycoprotein, which acts as a cofactor to activated protein C in the degradation of coagulation factors Va and VIIIa. It has been proposed that protein S has an additional function as a growth factor. Protein S and a structurally similar protein, Gas6, have been found to stimulate members of the Axl/Sky family of receptor tyrosine kinases. Human Gas6 is able to activate Axl and Sky. In contrast, while bovine protein S activates human Sky and its murine homologue, human protein S activates murine Sky but not the human receptor. In the present investigation, we studied the structural background of this species difference. Using protein S chimeras with domains from human and bovine origin, we found that only those chimeras with the steroid-hormone-binding globulin-like (SHBG) region from bovine protein S activate human Sky, indicating that the SHBG region is essential for the interaction. This observation was confirmed by inhibition of Sky phosphorylation by C4b-binding protein, a plasma protein that interacts tightly with the SHBG region of protein S. Another chimeric molecule, composed of the N-terminal 4-carboxyglutamic-acid-containing domain (Gla domain) and the two epidermal-growth-factor-like domains of human factor IX, and the SHBG region of bovine protein S, stimulated the receptor less efficiently. Antibodies directed against the Gla domain of protein S, inhibited the activation of human Sky by bovine protein S. These results indicate that the N-terminal domains of protein S are not essential for activation of the receptor, but contribute to the affinity of the interaction. Our data suggest that protein S might be a ligand of Sky in some species despite the lack of activity of human protein S on human Sky. The bovine/human protein S species difference will be a useful model to establish the structural requirements for the interaction between Sky and its ligands.

Animals↗

PubMed1997

SHBG region of the anticoagulant cofactor protein S: secondary structure prediction, circular dichroism spectroscopy, and analysis of naturally occurring mutations.

Protein S (PS) and growth arrest specific factor 6 (GAS6) are vitamin K-dependent proteins with similar structures. They are mosaic proteins possessing a carboxyl-terminal region presenting sequence similarity with plasma sex hormone binding globulin (plasma SHBG), although apparently not involved in steroid binding. The SHBG-like modules have sequence similarity with the G repeats of the chain A of laminin. Laminin G repeats have been reported to contain mainly beta-strands (about 40-50%) but no or little alpha structure by circular dichroism (CD) spectroscopy. Secondary structure predictions carried out in the present work unexpectedly showed a 20 to 27% helices content in the SHBG region of PS/GAS6 (about 100 residues), while plasma SHBG and laminin G repeats had around 10% helices. CD measurements for human PS indicated also that its SHBG region had about 100 residues in alpha-helical structure. These data suggest that the SHBG region of PS/GAS6 on the one hand, and the laminin G repeats and possibly plasma SHBG on the other hand, could present important structural differences. Previously reported polymorphisms and point mutations leading to PS deficiency and thrombophilia have been analyzed with our structural predictions. We found a good agreement between these structural predictions, CD measurements, experimental and clinical data. This information allows us to gain insights into the three-dimensional structure of PS that will be helpful for the design of new experiments and future clinical investigations.

Amino Acid Sequence↗

PubMed1995

Serum amyloid P component binding to C4b-binding protein.

Human C4b-binding protein (C4BP), which is a regulator of the classical complement pathway C3 convertase, forms high affinity complexes with anticoagulant protein S and with the pentraxin serum amyloid P component (SAP). SAP is a plasma protein present in all amyloid deposits. Recently, SAP was shown to inhibit the complement regulatory functions of C4BP. In this investigation, we have studied the structural requirements for the C4BP-SAP interaction. C4BP was subjected to chymotrypsin digestion, which yielded two major fragments corresponding to the central core (160 kDa) and to the cleaved-off tentacles (48 kDa). SAP-Sepharose specifically bound the 160-kDa fragment, suggesting that the central core of C4BP contains the binding site for SAP. In a quantitative affinity chromatography assay, the dissociation constants for binding of intact C4BP and of the 160-kDa central core fragment to SAP were found to be 30 and 70 nM, respectively. Recombinant C4BP composed of only alpha-chains bound SAP with similar affinity (Kd = 22 nM), whereas nonglycosylated recombinant alpha-chain C4BP (synthesized in the presence of tunicamycin) bound SAP with lower affinity (Kd = 126 nM). This suggests that the carbohydrate moiety of the central core of C4BP is important for binding of C4BP to SAP in contrast to the C4BP beta-chain, which is not required. EDTA, heparin, and phosphorylethanolamine as well as a peptide comprising amino acids 27-39 of SAP were found to completely displace C4BP from the SAP matrix. Moreover, the immobilized SAP peptide bound C4BP in a reaction that, in contrast to the C4BP-SAP interaction, was not dependent on calcium.

Amino Acid Sequence↗

PubMed1995

Inhibition of Alzheimer beta-peptide fibril formation by serum amyloid P component.

A 39-43-amino acid residue-long fragment (beta-peptide) from the amyloid precursor protein is the predominant component of amyloid deposits in the brain of individuals with Alzheimer's disease. Serum amyloid P component (SAP) is present in all types of amyloid, including that of Alzheimer's disease. We have used an in vitro model to study the effects of purified SAP on the fibril formation of synthetic Alzheimer beta-peptide 1-42. SAP was found to inhibit fibril formation and to increase the solubility of the peptide in a dose-dependent manner. At a 5:1 molar ratio of A beta 1-42 peptide to SAP, fibril formation was completely inhibited, and approximately 80% of the peptide remained in solution even after 4 days of incubation. At lower SAP concentrations, e.g. at peptide to SAP ratio of 1000:1, short fibrillar like structures, lacking amyloid characteristics, were formed. These structures frequently contained associated SAP molecules, suggesting that SAP binds to the polymerizing peptide in a reaction which prevented further fibril formation.

Alzheimer Disease↗

PubMed1995

The muscle isoform of 6-phosphofructo 2-kinase/fructose 2,6-bisphosphatase of the teleost Sparus aurata: relationship with the liver isoform.

The liver isoform of 6-phosphofructo 2-kinase/fructose 2,6-bisphosphatase of the teleost fish Sparaus aurata has several characteristics similar to the skeletal muscle isoform of mammals. In order to ascertain the relation between muscle and liver isoforms in teleost, 6-phosphofructo 2-kinase/fructose 2,6-bisphosphatase was purified from skeletal muscle of S. aurata. The muscle isozyme is composed of subunits with a molecular weight of 54 kDa, is bifunctional, and has an activity ratio kinase to bisphosphatase of 2.5. Muscle 6-phosphofructo 2-kinase is not sensitive to glycerol 3-phosphate inhibition and has noncooperative KmATP, higher than the liver isozyme. Thus, the kinetic characteristics of the muscle were distinguishable from the liver isozyme. Furthermore, the muscle isozyme is not a substrate of cAMP-dependent protein kinase. Despite those differences, two polyclonal antibodies raised against purified liver and muscle isozymes from S. aurata are not able to distinguish between them. Both antisera recognize with lower affinity recombinant rat liver 6-phosphofructo 2-kinase/fructose 2,6-bisphosphatase. A third antibody raised against the rat liver isozyme was also able to immunoprecipitate the teleost enzymes. The close immunological properties found suggest that S. aurata isozymes share epitopes in common. Considering the kinetic and immunological data reported, it is likely that the skeletal muscle/liver isozymes in teleost are products of a differentially spliced transcript of the same gene, as it is in rat. As those species are distant in vertebrate evolution, the similitude suggest that a common ancestral gene is involved in the muscle/liver 6-phosphofructo 2-kinase/fructose 2,6-bisphosphatase system in vertebrates.

Animals↗

PubMed1995

Expression and characterization of a recombinant C4b-binding protein lacking the beta-chain.

C4b-binding protein (C4BP) is a high-molecular-mass glycoprotein which contains binding sites for complement component C4b, anti-coagulant vitamin K-dependent protein S and serum amyloid P component (SAP). The major form of C4BP in plasma is composed of seven identical alpha-chains and a single beta-chain. We have expressed full-length cDNA for the alpha-chain in a eukaryotic expression system and characterized functional properties of non-beta-chain-containing C4BP. During synthesis, recombinant alpha-chains polymerized into two different high-molecular-mass C4BP forms which were composed of seven or eight alpha-chains. Recombinant C4BP bound C4(H2O) (used instead of C4b) equally as well as native C4BP, functioned equally as well as factor I cofactor in the degradation of C4(H2O) and bound to SAP. In contrast, the recombinant C4BP did not bind protein S and therefore did not inhibit the ability of protein S to function as a cofactor to activated protein C. Tunicamycin treatment of the transfected cells prevented N-linked glycosylation, but did not affect polymerization of the alpha-chains into a high-molecular-mass C4BP. The non-glycosylated C4BP had comparable properties to glycosylated C4BP in several functional assays. These results demonstrate polymerization of C4BP alpha-chains to be independent both of the beta-chain and of the N-linked carbohydrates. Moreover, N-linked carbohydrates and the beta-chain were neither required for the ability of C4BP to bind C4b and to function as factor I cofactor nor for the interaction with SAP.

Binding, Competitive↗

PubMed1995

Resistance to activated protein C as an additional genetic risk factor in hereditary deficiency of protein S.

Inherited resistance to activated protein C (APC), which is caused by a single point mutation in the gene for factor V, is a common risk factor for thrombosis. In this study, the prevalence of APC resistance in 18 unrelated thrombosis-prone families with inherited protein S deficiency was investigated to determine its role as additional genetic risk factor for thrombosis. In addition, a detailed evaluation of the clinical manifestations in these families was performed. Venous thrombotic events had occurred in 47% of the protein S-deficient patients (64/136) and in 7% of relatives without protein S deficiency (14/191). As estimated from Kaplan-Meier analysis, 50% of protein S-deficient family members and 12% of those without protein S deficiency had had manifestation of venous thromboembolism at the age of 45 years. The age at the first thrombotic event ranged from 10 to 81 years (mean, 32.5 years) and a large intrafamilial and interfamilial variability in expression of thrombotic symptoms was seen. The factor V gene mutation related to APC resistance was present in 6 (38%) of 16 probands available for testing; in total, the mutation was found in 7 (39%) of the 18 families. In family members with combined defects, 72% (13/18) had had thrombosis as compared with 19% (4/21) of those with only protein S deficiency and 19% (4/21) of those with only the factor V mutation. In conclusion, APC resistance was found to be highly prevalent in thrombosis-prone families with protein S deficiency and was an additional genetic risk factor for thrombosis in these families. The results suggest thrombosis-prone families with protein S deficiency often to be affected by yet another genetic defect.

Adolescent↗

PubMed1995

Evaluation of the relationship between protein S and C4b-binding protein isoforms in hereditary protein S deficiency demonstrating type I and type III deficiencies to be phenotypic variants of the same genetic disease.

Type III protein S deficiency is characterized by a low plasma level of free protein S, whereas the total concentration of protein S is normal. In contrast, both free and total protein S levels are low in type I deficiency. To elucidate the molecular mechanism behind the selective deficiency of free protein S in type III deficiency, the relationship between the plasma concentrations of beta-chain containing isoforms of C4b-binding protein (C4BP beta+) and different forms of protein S (free, bound, and total) was evaluated in 327 members of 18 protein S-deficient families. In normal relatives (n = 190), protein S correlated well with C4BP beta+, with free protein S (96 +/- 23 nmol/L) being equal to the molar excess of protein S (355 +/- 65 nmol/L) over C4BP beta+ (275 +/- 47 nmol/L). In protein S-deficient family members (n = 117), the equimolar relationship between protein S (215 +/- 50 nmol/L) and C4BP beta+ (228 +/- 51 nmol/L), together with the high affinity of the interaction, resulted in low levels of free protein S (16 +/- 10 nmol/L). Free protein S levels were distinctly low in protein S-deficient members, whereas in 47 of the protein S-deficient individuals, the concentration of total protein S was within the normal range, which fulfils the criteria for type III deficiency. The remaining 70 had low levels of both total and free protein S and, accordingly, would be type I deficient. Coexistence of type I and type III deficiency was found in 14 families, suggesting the two types of protein S deficiency to be phenotypic variants of the same genetic disease. Interestingly, not only protein S but also C4BP beta+ levels were decreased in orally anticoagulated controls and even more so in anticoagulated protein S-deficient members, suggesting that the concentration of C4BP beta+ is influenced by that of protein S. In conclusion, our results indicate that type I and type III deficiencies are phenotypic variants of the same genetic disease and that the low plasma concentrations of free protein S in both types are the result of an equimolar relationship between protein S and C4BP beta+.

Adolescent↗

PubMed1995

cDNA structure of rabbit C4b-binding protein alpha-chain. Preserved sequence motive in complement regulatory protein modules which bind C4b.

A full length cDNA clone for the alpha-chain of the rabbit complement regulatory protein C4b-binding protein (C4BP) was isolated from a liver cDNA library. The clone encoded an open reading frame of 597 amino acids, which included a signal peptide, eight short consensus repeats (SCR) and a carboxy terminal non-repeat region. Gel filtration of rabbit plasma and testing of fractions for factor I cofactor activity (C4BP-like) revealed two peaks of activity, the one with highest molecular weight corresponding in size to that of human C4b-binding protein. Comparison of the rabbit C4BP alpha-chain sequence with other SCR containing C3b/C4b binding proteins revealed highest sequence similarities between the second SCRs in C4BP from rabbit, human and murine species and SCRs at corresponding position in complement receptor 1 (CR1) whereas in decay accelerating factor (DAF), the third SCR was most similar. A conserved sequence motive was identified in these C4b-binding SCRs.

Amino Acid Sequence↗

PubMed1994

Differential regulation of alpha and beta chains of C4b-binding protein during acute-phase response resulting in stable plasma levels of free anticoagulant protein S.

Regulation of C4b-binding protein (C4BP) isoforms during acute phase and its relationship to the plasma concentration of free protein S was elucidated. An assay for beta chain containing C4BP (C4BP beta+) was developed and the concentrations of total C4BP, C4BP beta+, total, free, and bound protein S were measured in patients with acute-phase response. Even though total C4BP was increased to 162% (mean value) of controls, the corresponding value of C4BP beta+ was only 122%. In the acute-phase group, total protein S was increased to the same extent as C4BP beta+ (mean value of 124%), whereas free protein S was not decreased. In controls, total and bound protein S correlated with total C4BP and C4BP beta+. However, in the acute-phase group, the correlation between bound protein S and total C4BP was lost, although the correlation between C4BP beta+ and protein S remained. The present results suggest stable levels of free protein S during acute phase to be the result of differential regulation of C4BP alpha- and beta-chain expression, and the concentration of free protein S to be the resulting molar excess of protein S over C4BP beta+. This mechanism ensures functional levels of free anticoagulant protein S despite high levels of C4BP.

Acute-Phase Proteins↗