PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Complement C1r”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 163 records · Page 9Linked to original sources
PubMed1991

C1R subcomponent polymorphism in Japanese: description of a new allele.

The polymorphism of C1R was investigated in 570 unrelated Japanese individuals using isoelectric focusing and immunoblotting. A total of 11 different C1R phenotypes including a new pattern designated C1R 11-1 were observed. The allele frequencies were C1R*1 = 0.4561, C1R*2 = 0.3377, C1R*5 = 0.1956, C1R*8 = 0.0088 and C1R*R (C1R*9 and C1R*11) = 0.0018. The population data fitted the Hardy-Weinberg equilibrium. The C1R polymorphism in Japanese was shown to be controlled by 3 common alleles, C1R*1, C1R*2 and C1R*5, as compared to Caucasians where only the former 2 are present commonly. This complement system can be a useful genetic marker for anthropological studies.

Alleles↗
PubMed1985

Autocatalytic activation of C1r subcomponent of the first component of human complement.

Autoactivation of the proenzyme form of a subunit of the first component (C1r) was performed in the presence and absence of diisopropyl fluorophosphate (DFP). The time-course of autoactivation of zymogen C1r followed a sigmoidal curve and was accelerated by addition of the enzyme C1r and by increasing the concentration of C1r, suggesting that autoactivation of C1r consists of two intermolecular reactions, i.e. zymogen(C1r)- and enzyme(C1r)-catalyzed reactions. In the presence of 10 mM DFP, the enzyme-catalyzed autoactivation of C1r was completely inhibited, while the zymogen-catalyzed autoactivation still proceeded depending upon C1r concentration. These results suggested that the zymogen-catalyzed autoactivation of C1r is a DFP-insensitive second-order reaction and is mediated by an active site generated in a single chain C1r through a conformational change (Kassahara et al. (1982) FEBS lett. 141, 128-131). Based on these results, a possible reaction process of autoactivation of C1r was proposed, as follows: (formula; see text) where C1r represents a conformational isomer which catalyzes the autoactivation of C1r, and the rate constants, k2 and k3, are of second-order. Utilizing a computer, we simulated the autoactivation of C1r and found the above scheme to be a reasonable model of C1r autoactivation. Evidence which supports the formation of a conformational isomer of C1r, C1r, as an intermediate in its autoactivation was also obtained by a surface radiolabeling method.

Complement Activating Enzymes↗
PubMed1980

Purified proenzyme C1r. Some characteristics of its activation and subsequent proteolytic cleavage.

1. Upon incubation for 1 h at 37 degrees C, proenzymic C1r was activated by a proteolytic cleavage comparable to that observed in vivo; after reduction and alkylation, two fragments of apparent molecular weights 57 000 and 35 000 were evident on sodium dodecyl sulphate (SDS)-polyacrylamide gel electrophoresis. The activation kinetics were slightly sigmoidal and nearly independent of C1r concentration. They were characterized by a marked thermal dependence (activation energy = 45 kcal/mol). The reaction was inhibited by calcium and p-nitrophenyl-p'-guanidinobenzoate, but poorly sensitive to di-isopropyl phosphorofluoridate. The dependence of the activation rate on pH was unusual; it decreased progressively in the acid range (pH 4.5-6.5) which coincides with the dissociation of the C1r-C1r dimer. Above pH 6.5, the rate increased slightly and showed no clear maximum. These results are consistent with an intramolecular autocatalytic activation mechanism involving the pro-site of each subunit of the C1r-C1r dimer. 2. During a 5 h incubation period at 37 degrees C, C1r underwent two proteolytic cleavages which led to the successive removal of two fragments, alpha (35 000) and beta (7000-11 000) from each subunit, leaving a dimeric molecule of reduced size (Mr = 110 000; s20,w = 6.1 S). The proteolytic process was nearly independent of C1r concentration and characterized by a pH optimum at 8.5-9.0, and a high activation energy (36.8 kcal/mol). Calcium and p-nitrophenyl-p'-guanidinobenzoate, and also di-isopropyl phosphorofluoridate and benzamidine were inhibitors of this reaction. The product, C1r II, retained the original antigenic properties of C1r and a functional active site, but lost the capacity to bind C1s. These results are consistent with an autocatalytic intramolecular proteolysis mediated by the active site of each subunit of the C1r-C1r dimer.

Complement Activating Enzymes↗
PubMed1989

Isolation and functional characterization of the proenzyme form of the catalytic domains of human C1r.

The proenzyme form of C1r catalytic domains was generated by limited proteolysis of native C1r with thermolysin in the presence of 4-nitrophenyl-4'-guanidinobenzoate. The final preparation, isolated by high-pressure gel permeation in the presence of 2 M-NaCl, was 70-75% proenzyme and consisted of a dimeric association of two gamma B domains, each resulting from cleavage of peptide bonds at positions 285 and 286 of C1r. Like native C1r, the isolated domains autoactivated upon incubation at 37 degrees C. Activation was inhibited by 4-nitrophenyl-4'-guanidinobenzoate but was nearly insensitive to di-isopropyl phosphorofluoridate; likewise, compared to pH 7.4, the rate of activation was decreased at pH 5.0, but was not modified at pH 10.0. In contrast, activation of the (gamma B)2 domains was totally insensitive to Ca2+. Activation of the catalytic domains, which was correlated with an irreversible increase of intrinsic fluorescence, comparable with that previously observed with native C1r [Villiers, Arlaud & Colomb (1983) Biochem. J. 215, 369-375], was reversibly inhibited at high ionic strength (2 M-NaCl), presumably through stabilization of a non-activatable conformational state. Detailed comparison of the properties of native C1r and its catalytic domains indicates that the latter contain all the structural elements that are necessary for intramolecular activation, but probably lack a regulatory mechanism associated with the N-terminal alpha beta region of C1r.

Catalysis↗
PubMed1982

Fluid-phase interaction of C1 inhibitor (C1 Inh) and the subcomponents C1r and C1s of the first component of complement, C1.

Interactions between proenzymic or activated complement subcomponents of C1 and C1 Inh (C1 inhibitor) were analysed by sucrose-density-gradient ultracentrifugation and sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. The interaction of C1 Inh with dimeric C1r in the presence of EDTA resulted into two bimolecular complexes accounting for a disruption of C1r. The interaction of C1 Inh with the Ca2+-dependent C1r2-C1s2 complex (8.8 S) led to an 8.5 S inhibited C1r-C1s-C1 Inh complex (1:1:2), indicating a disruption of C1r2 and of C1s2 on C1 Inh binding. The 8.5 S inhibited complex was stable in the presence of EDTA; it was also formed from a mixture of C1r, C1s and C1 Inh in the presence of EDTA or from bimolecular complexes of C1r-C1 Inh and C1s-C1 Inh. C1r II, a modified C1r molecule, deprived of a Ca2+-binding site after autoproteolysis, did not lead to an inhibited tetrameric complex on incubation with C1s and C1 Inh. These findings suggest that, when C1 Inh binds to C1r2-C1s2 complex, the intermonomer links inside C1r2 or C1s2 are weakened, whereas the non-covalent Ca2+-independent interaction between C1r2 and C1s2 is strengthened. The nature of the proteinase-C1 Inh link was investigated. Hydroxylamine (1M) was able to dissociate the complexes partially (pH 7.5) or totally (pH 9.0) when the incubation was performed in denaturing conditions. An ester link between a serine residue at the active site of C1r or C1s and C1 Inh is postulated.

Binding Sites↗
PubMed1981

Clr and Cls subcomponents of human complement: two serine proteinases lacking the 'histidine-loop' disulphide bridge.

The N-terminal amino acid sequence of human C1s b chain has been extended to 52 residues. The histidine residue involved in the charge-relay system is located at position 38, whereas the histidine-loop disulphide bridge is missing. So far, human complement sub-components C1r and C1s are the only known mammalian serine proteinases lacking this disulphide bridge.

Amino Acid Sequence↗
PubMed1982

Fluid phase activation of proenzymic C1r purified by affinity chromatography.

1. Proenzymic C1r was purified from human plasma in a two-step technique involving indirect affinity chromatography on Sepharose Ig anti-C1s. The capacity of C1r to monomerize at pH 5.0 and to redimerize at neutral pH was used for selective elution of C1r. The yield in purified C1r was 39% from plasma; no trace of contaminating serine proteases was detected from [3H]diisopropyl phosphorofluoridate labelling of C1r. 2. C14 was able to undergo a two-way autoactivation: an intramolecular catalytic process catalysed by proenzymic C1r itself and an intermolecular reaction catalysed by activated C1r formed in the process of the reaction. DFP (5mM) and C1 Inh at a C1 Inh/C1r ratio of 1:1 were effective on the solely intermolecular activation, leading to partial inhibition of the autoactivation from proenzymic C1r: C1r formed during the activation was titrated by the inhibitors. Calcium, high ionic strength or acid pH decreased C1r activation. The pH effect was characterized by a slowed-down reaction below pH 6.0 and no net influence at values as high as 10.5. The two types of activation developed similarly as a function of pH. 3. Peripheral iodination of C1r revealed differences in label distribution between proenzymic (A chain moiety 48%, B chain moiety 52%) and activated C1r (A chain 20%, B chain 80%). Two different conformational states of C1r were also suggested by 125I-labelling at different temperatures.

Calcium↗
PubMed1993

Genetic deficiencies of the complement system and association with disease--early components.

Genetic deficiency of one of the early components of the classical pathway of complement (C1q, C1r, C1s, C4 and C2) is often associated with clinical symptoms and immunochemical abnormalities common in idiopathic autoimmune diseases, such as lupus erythematosus, but also with an increased incidence of various, local and generalized infections. These observations are consistent with the current view of the complement system's role in handling immune complexes and combating microbial invasion. However, the absence of absolute correlations in these experiments of nature suggests that genetic defects of the classical pathway act only epistatically to other host factors and the primary etiologies of the associated diseases. In contrast, the strong association of properdin and factor D deficiency with serious infections caused by encapsulated Gram-negative bacteria suggests a more immediate involvement of the alternative pathway in a specific segment of immunity and its pathology. This concept is also supported by the primordial role of the alternative pathway in the evolution of the complement system and the apparent lethality of factor B deficiency. The gene structures of most of these early components have now been elucidated providing the basis for detailed analyses of the defective alleles, the determination of carrier status, and prenatal diagnosis.

Complement C1↗
PubMed1985

Identification of the peptide bond cleaved during activation of human C1r.

CNBr cleavage of unreduced proenzyme C1r yielded fragment CP2b, isolated by gel filtration and high-pressure gel permeation chromatography. This fragment (approximately Mr 55 000) comprised at least 4 disulphide-linked peptides, which were separated by gel filtration after reduction and alkylation. Peptide CP2bRA4, overlapping the A- and B-chain regions in proenzyme C1r was digested by V8 staphylococcal protease, and the digest separated by reversed-phase HPLC. N-terminal sequence analysis of peptide CP2bRA4SP9 established that C1r activation involves the cleavage of a single Arg-Ile bond, located in the sequence: ... Gln-Arg-Gln-Arg-Ile-Ile-Gly-Gly ... .

Amino Acids↗
PubMed1987

Identification of erythro-beta-hydroxyasparagine in the EGF-like domain of human C1r.

Previous studies [(1987) Biochem. J. 241, 711-720] have shown that position 150 of human C1r is occupied by a modified amino acid that, after acid hydrolysis, yields erythro-beta-hydroxyaspartic acid. In view of further investigations on the nature of this residue, peptide CN1a T8/T9 TL8 (positions 147-155) was isolated from C1r A chain by CNBr cleavage followed by enzymatic cleavages by trypsin and thermolysin. Amino acid analysis, sequential Edman degradation and FAB-MS of this peptide indicate that the residue at position 150 is an erythro-beta-hydroxyasparagine resulting from post-translational hydroxylation of asparagine.

Amino Acids↗
PubMedDate not supplied

[Biochemical data on C1 intrinsic activation (author's transl)].

C1 activation can be triggered by immune complexes and various effectors such as extrinsic proteases, bacterial or viral membranes, polyanions and polysaccharides. The basic mechanism of activation involves a limited proteolytic cleavage of C1r, with the generation of a proteolytic activity. Highly purified proenzymic C1r was obtained in high yield from human plasma by an indirect affinity chromatography step. Activation of isolated C1r in a fluid phase proceeded according to two distinct coexisting mechanisms: 1) an autocatalytic intradimer activation mediated by the pro-site of non-activated C1r; 2) an autocatalytic interdimer proteolysis triggered by nascent activated C1r formed in the course of the first reaction. DFP and C1-inhibitor did not have any effect on the first mechanism but were able to block the second mechanism. C1 activation is discussed in the light of recent results obtained by others from electron microscopy, and a tentative model is proposed.

Antigen-Antibody Complex↗
PubMed1989

The alpha 1/alpha 2 domains of class I HLA molecules confer resistance to natural killing.

The expression of transfected HLA class I Ag has previously been shown to protect human target cells from NK-mediated conjugation and cytolysis. In this same system, transfected H-2 class I Ag fail to impart resistance to NK. In this study, we have mapped the portion of the HLA class I molecule involved in this protective effect by exploiting this HLA/H-2 dichotomy. Hybrid class I genes were produced by exon-shuffling between the HLA-B7 and H-2Dp genes, and transfected into the class I Ag-deficient B-lymphoblastoid cell line (B-LCL) C1R. Only those transfectants expressing class I Ag containing the alpha 1 and alpha 2 domains of the HLA molecule are protected from NK, suggesting the "protective epitope" is located within these domains. Since a glycosylation difference exists between HLA and H-2 class I Ag within these domains (i.e., at amino acid residue 176), the role of carbohydrate in the class I protective effect was examined. HLA-B7 mutant genes encoding proteins which either lack the normal carbohydrate addition site at amino acid residue 86 (B7M86-) or possess an additional site at residue 176 (B7M176+) were transfected into C1R. Transfectants expressing either mutant HLA-B7 Ag were protected from NK. Thus, carbohydrate is probably not integral to a class I "protective epitope." The potential for allelic variation in the ability of HLA class I Ag to protect C1R target cells from NK was examined in HLA-A2, A3, B7, and Bw58 transfectants. Although no significant variation exists among the HLA-A3, B7, and Bw58 alleles, HLA-A2 appears unable to protect. Comparison of amino acid sequences suggests a restricted number of residues which may be relevant to the protective effect.

Amino Acid Sequence↗
PubMed1991

The A5 antigen, a candidate for the neuronal recognition molecule, has homologies to complement components and coagulation factors.

The A5 antigen is a neuronal cell surface protein of Xenopus presumed to be involved in the neuronal recognition between the optic nerve fibers and the visual centers. Analyses of cDNA clones revealed that the A5 antigen is a class I membrane protein containing two different internal repeats in the extracellular segment. The first repeat bears homology to domain III of complement components C1r and C1s, and the second repeat is homologous to the C1 and C2 domains of coagulation factors V and VIII. The mRNA for the A5 antigen was present in retinal ganglion cells and visual center neurons. Nonneuronal cells in the peripheral and central nervous systems did not express the mRNA for the A5 antigen.

Amino Acid Sequence↗
PubMed1992

Invertebrate aspartyl/asparaginyl beta-hydroxylase: potential modification of endogenous epidermal growth factor-like modules.

An invertebrate alpha-ketoglutarate-dependent aspartyl/asparaginyl beta-hydroxylase, which posttranslationally hydroxylates specific aspartyl or asparaginyl residues within epidermal growth factor-like modules, was identified, partially purified and characterized. Preparations derived from two insect cell lines catalyzed the hydroxylation of the expected asparaginyl residue within a synthetic epidermal growth factor-like module. This activity was found to be similar to that of the purified mammalian aspartyl/asparaginyl beta-hydroxylase with respect to cofactor requirements, stereochemistry and substrate sequence specificity. Furthermore, recombinant human C1r, expressed in an insect cell-derived baculovirus expression system, was also found to be hydroxylated at the expected asparaginyl residue. Thus, these results establish the potential for invertebrate aspartyl/asparaginyl hydroxylation. Since several invertebrate proteins known to be required for proper embryonic development contain a putative consensus sequence that may be required for hydroxylation, the studies presented here provide the basis for further investigations concerned with identifying hydroxylated invertebrate proteins and determining their physiologic function.

Amino Acid Sequence↗
PubMed1986

Purification, identification and characterization of chicken C1q, a subcomponent of the first component of complement.

A component, having the equivalent haemolytic activity to that of human complement subcomponent C1q, was purified by a combination of precipitation with EGTA, gel filtration, ion exchange and adsorption chromatography from chicken serum. Yields ranged from 8 to 15 mg/litre of serum. The finally purified preparation generates full Cl haemolytic activity when assayed with human complement subcomponents C1r and C1s, and have been identified as chicken C1q. The molecular weight of undissociated C1q, as estimated on polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate (SDS), is 504,000. Under dissociating but non-reducing conditions, the C1q was shown to consist of 2 subunits having molecular weights of 52,700 and 51,200 in a molar ratio of 2:1. On reduction, the 52,700 molecular weight subunit gave chains with molecular weights of 25,900 and 24,800 in equimolar ratio, and the 51,200 molecular weight subunit decreased to 24,800. The C1q contains hydroxyproline, hydroxylysine, a high percentage of glycine and approximately 7% carbohydrate. Collagenase digestion of C1q caused a rapid loss of haemolytic activity and produced much smaller peptide fragments.

Amino Acids↗