Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Complement Factor I”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 181 records · Page 10Linked to original sources
PubMed1995

Analysis of the short consensus repeats of human complement factor B by site-directed mutagenesis.

Human factor B is required for the initiation and propagation of the complement alternative pathway. It also participates in the amplification of the complement classical pathway. Alone, factor B is a zymogen with little known biochemical activity, but in the context of the alternative pathway convertases, the factor B serine protease is activated in a process that first involves the association with C3b and subsequently the cleavage of factor B into two fragments, Ba and Bb. Ba, the NH2-terminal fragment, is composed mainly of three tandem short consensus repeats, globular domains found in other complement proteins. It dissociates from the convertase during assembly, leaving the active C3 convertase, C3bBb. Previous reports suggest that the Ba region may be instrumental in convertase assembly. This hypothesis was tested using site-directed mutagenesis of recombinant factor B and monoclonal antibody epitope mapping to evaluate the relative importance of specific short consensus repeat amino acid residues. Three sites of interest were identified. Site 1 is a stretch of 19 contiguous amino acids in short consensus repeat 1 that form the epitope of a monoclonal antibody that effectively blocks factor B function. Site 2, composed of 6 contiguous amino acids in short consensus repeat 2, and site 3, consisting of 7 contiguous amino acids in short consensus repeat 3, were defined by mutations that reduce factor B hemolytic activity to 3% or less. Further analyses indicated that sites 2 and 3 contribute to factor B-C3b interactions.

Amino Acid Sequence↗
PubMed1987

Bactericidal capacity against Neisseria meningitidis of normal human serum and sera with functional deficiencies of the third and eight complement factor.

The bactericidal capacity of serum with C3 deficiency secondary to circulating C3 nephritic factor, serum with C8 deficiency and normal human serum were assessed in vitro against Neisseria meningitidis groups A-C. Normal human serum and C8-deficient serum, originating from a 28-year-old male with two episodes of meningococcal meningitis, showed significant bactericidal capacity against meningococci groups A and B. Against group C meningococci the C8-deficient serum revealed significant bactericidal capacity, whereas normal human serum showed no bactericidal effect. Serum with C3 deficiency, obtained from a 16-year-old female with two episodes of meningococaemia, showed no bactericial effect against meningococci groups A-C. Incubation of normal human serum and C8-deficient serum with isolated nephritic factor resulted in C3 depletion and abolished the bactericidal effect.

Adolescent↗
PubMed1995

Location of the complement factor H binding site on streptococcal M6 protein.

The surface M protein of group A streptococci binds factor H, a regulatory protein of the alternative complement pathway, which may contribute to the antiphagocytic activity of the M molecules. To locate the factor H binding domain in the alpha-helical coiled-coil structure of the M molecule, the M protein was cleaved with pepsin at pH 5.8, which separates the molecule approximately in half. Western blot (immunoblot), amino acid sequence, and mass spectrometric analyses revealed that factor H bound to a 14.6-kDa C-terminal fragment of the M molecule. Competitive inhibition of factor H binding to the 14.6-kDa fragment with M protein peptides localized the binding site to amino acids 256 to 292. This segment is located within the surface-exposed region of the M6 protein, identified as the C-repeat region, whose sequence is conserved among heterologous M and M-like molecules. These studies also identified a second pepsin-susceptible site with the sequence ELAK located within the cell wall-associated region of the M molecule.

Amino Acid Sequence↗
PubMed1991

Oligomeric domain structure of human complement factor H by X-ray and neutron solution scattering.

Factor H is a regulatory component of the complement system. It has a monomer Mr of 150,000. Primary structure analysis shows that the polypeptide is divided into 20 homologous regions, each 60 amino acid residues long. These are independently folding domains and are termed "short consensus repeats" (SCRs) or "complement control protein" (CCP) repeats. High-flux synchrotron X-ray and neutron scattering studies were performed in order to define its solution structure in conditions close to physiological. The Mr of factor H was determined as 250,000-320,000 to show that factor H is dimeric. This structure is maintained at concentrations between 1 and 11 mg/mL in the pH range 5-9. Zn2+ ions are an inhibitor of C3b cleavage by factor I, a reaction in which factor H acts as a cofactor. Additions of Zn2+ to factor H caused it to form oligomers containing 4-10 monomers. The radius of gyration RG of native factor H by X-rays or by neutrons in 0% or 100% 2H2O buffers is not measurable but is greater than 12.5 nm. Two cross-sectional radii of gyration RXS-1 and RXS-2 were determined as 3.0-3.1 and 1.8 nm, respectively. Analyses of the cross-sectional intensities show that factor H is composed of two distinct subunits. The RXS-1 corresponds to the cross-sectional properties of both subunits and exhibits an unusual radiation dependence on the X-ray flux. Since RXS-2 is close to the corresponding RXS of C4b binding protein (91% of which is formed from SCR/CCP domains), it is inferred that the SCR/CCP domains of factor H and C4b binding protein have similar solution structures. The use of hydrodynamic spheres to reproduce literature sedimentation coefficients of 5.5-5.6 S showed that these were compatible with a V-shaped arrangement of two rods (36 spheres each, length 87 +/- 5 nm) joined at an angle of 5 degrees. The use of a similar arrangement of 244 spheres arranged in two rods (length 77 nm) to fit the experimental X-ray and neutron scattering curves showed that the two rods are joined at an angle of 5 degrees. This model corresponds to an actual RG of 21-23 nm. The separation between each SCR/CCP in factor H is close to 4 nm. In the solution structure of factor H, the SCR/CCP domains are in a highly extended conformation.

Complement C3b↗
PubMed1993

Adsorption of complement factor D by polyacrylonitrile dialysis membranes.

Factor D, an essential enzyme of the alternative pathway (AP) of complement, accumulates in end-stage renal failure (ESRF). Polyacrylonitrile (PAN) membrane activates complement poorly and has been shown to adsorb C3a, the main anaphylatoxin released during complement activation. In the present work we investigated whether factor D might be adsorbed on PAN. In vitro there was a loss of hemolytic factor D when normal human serum (NHS) was incubated with PAN dialysis fibers, whereas no loss was observed with cuprophan (Cu) fibers. There was a dose and time dependent binding of purified radiolabeled factor D to PAN but not to Cu. The hemolytic function of factor D released from PAN by 2 M NaCl was normal. By contrast, factor D was inactive while adsorbed to PAN fibers. When 50 ml of NHS or 100 ml of whole blood were passed through a new hollow fiber PAN dialyzer 95% of factor D was adsorbed. The eluate from a PAN filter which had been used for dialysis in a patient with ESRF contained 38.4 mg of hemolytic factor D, representing 34% of the proteins eluted. By immunoblotting, antigenic factor D from the PAN eluate was identical to purified human factor D. In six patients there was a 81.4% decrease in hemolytic factor D in blood after dialysis with PAN, contrasting with a 9.6% decrease in those dialyzed with cellulose acetate. No factor D was found in the dialysis fluid of PAN dialyzers, indicating that PAN removed factor D mainly by adsorption. In conclusion, PAN has a significant capacity to adsorb factor D, a reaction that might contribute to the diminished capacity of PAN membrane to activate the AP of complement. Whether the efficient removal of large amounts of factor D might be beneficial in uremic patients remains to be defined.

Acrylic Resins↗
PubMed1990

Zinc ions inhibit factor I-mediated release of CR1-bound immune complexes and degradation of cell-bound complement factors C3b and C4b.

ZnCl2 exerted a dose-dependent inhibition of citrate-phosphate-dextrose (CPD) plasma-induced release of 125I-labelled BSA-anti-BSA immune complexes (IC) bound to complement receptor type 1 (CR1, CD35) in human whole blood. Maximal inhibition was observed at 10 mM of ZnCl2. Furthermore, the release of IC bound to erythrocyte (E)-CR1 by purified factor I, factor I-deficient serum plus purified factor I, or normal human serum was reduced by approximately 90%, 64%, and 52%, respectively, in the presence of 10 mM ZnCl2. The effect of ZnCl2 on factor I-mediated degradation of cell-bound C3b/C4b was also investigated employing CPD blood or E from a factor I-deficient donor. These cells expressed covalently bound C3b and C4b as demonstrated by a simple agglutination technique. Upon incubation of CPD whole blood with purified factor I, or of E with purified factor I or normal CPD plasma, the C-fragments were cleaved and the cells were no longer agglutinated by antibodies to C3c and C4c. The presence of ZnCl2 prevented this factor I-mediated degradation of C3b and C4b, as evidenced by the unaffected agglutination of the cells by the antibodies. We conclude that ZnCl2 inhibited factor I activity since: (1) release of complement-preopsonized IC from E-CR1 by purified factor I was markedly inhibited (90%) in the presence of ZnCl2, (2) preincubation of the cells with ZnCl2 caused only a moderate inhibition (32-38%) of the IC release, and (3) degradation by purified factor I of covalently cell-bound C3b and C4b was abrogated in the presence of 10 mM ZnCl2.

Animals↗
PubMed1997

Localization by site-directed mutagenesis of the site in human complement factor H that binds to Streptococcus pyogenes M protein.

M-protein receptors located on Streptococcus pyogenes cells are known to bind human plasma protein factor H. Human factor H is composed of 20 short consensus repeat (SCR) domains containing approximately 60 amino acids each. Factor H controls the activation of the alternative pathway of complement in plasma. We have scanned the entire human factor H molecule by site-directed deletion mutagenesis, expressed the recombinant proteins in insect cells using the baculovirus system, and measured the binding of different purified mutant proteins to three strains of S. pyogenes. These studies have revealed that recombinant factor H lacking SCR domains 6 to 10 does not bind to wild-type M+ S. pyogenes JRS4. Experiments performed with S. pyogenes JRS251, in which both C-repeat domains of M protein were deleted, demonstrated that all of the factor H mutant proteins bound weakly to these cells except those lacking the SCR region from domains 6 to 10. Neither human factor H nor any of the recombinant proteins bound to the M- strain JRS145. Our results indicate that the only binding site on human factor H that interacts with streptococcus M protein is located in SCR domains 6 to 10 of factor H and that regions of M protein outside the C-repeat domains are involved in binding factor H.

Animals↗
PubMed1988

Metabolism of complement factor D in renal failure.

Factor D is an essential enzyme of the alternative pathway of complement. Its plasma concentration increases approximately tenfold in end-stage renal failure (ESRF). To analyze its metabolism in humans, we injected purified radiolabelled factor D into 5 healthy individuals and 12 patients with various renal diseases or renal failure. Fractional metabolic rates (FMR) and extravascular/intravascular distributions (EV/IV) were calculated using a compartmental model. The FMR was very rapid in normal individuals (mean 59.6%/hr; range 74.1 to 50.5), significantly diminished in the five patients with ESRF (5.7%/hr; 7.0 to 2.8; P less than 0.004), and correlated well with the creatinine clearance (r = 0.89; P less than 0.001). The extrarenal catabolic rate was not modified in renal failure. Despite a significant inverse correlation between plasma levels of factor D and creatinine clearance [r = 0.68; P less than 0.002], factor D levels were not a sensitive indicator of renal function because the synthesis rate (SR) varied widely from one individual to another (mean SR: 62.9 micrograms/kg/hr; 14.9 to 136.5). Factor D synthesis was not significantly altered by renal function, and did not correlate with C-reactive protein, suggesting that factor D is not an acute phase protein. The proportion of intact factor D elimination in the urine was increased in patients with tubular dysfunction (up to 15% compared to less than 0.2% in normal individuals) confirming that under normal circumstances factor D is filtered through the glomerulus and catabolized by tubular cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Complement Activating Enzymes↗
PubMedDate not supplied

Hormonal regulation of complement factor B in human endometrium.

PROBLEM: Recent investigations have demonstrated the presence of complement components in human endometrium in a cycle-specific manner. Luteal phase endometrium has been shown to synthesize complement C3 de novo, whereas proliferative endometrium produces little or no C3. Likewise factor B, which is critical to the activation of the alternative pathway of complement, has been shown to be present only in the glandular epithelium of luteal phase endometrium. This investigation was designed to determine if factor B is present in the endometrium in a high progesterone state such as pregnancy or with exogenous progesterone treatment. METHOD: Endometrial biopsies were obtained from patients on progesterone therapy. The endometrium of early pregnancy was evaluated by obtaining biopsies from patients with ectopic pregnancies as well as from patients undergoing therapeutic termination. Immunohistochemistry was performed on each biopsy using monoclonal antibodies to factor B. RESULTS: Our results demonstrate the presence of factor B in the glandular epithelial cells of the endometrium of patients treated with exogenous progesterone therapy. Additionally, factor B was localized to the glandular compartment of the endometrium from patients with ectopic gestations. Interestingly, the evaluation of an implantation site from an early gestation demonstrated factor B in the maternal decidua only; trophoblast did not exhibit the presence of factor B. CONCLUSION: Factor B exists in the endometrium in a hormone-dependent manner and is not expressed in fetal tissue in early gestation.

Complement Factor B↗
PubMed1989

A new polymorphic variant of human complement factor I.

Sera from 305 individuals were typed for factor I, and a new variant, tentatively designated FI C, was found. All other samples were FI B except for seven samples from Chinese that were of the FI AB phenotype. This suggests that polymorphism of factor I may be rare in Caucasians.

Complement C3b Inactivator Proteins↗
PubMed1984

Localized heat urticaria associated with a decrease in serum complement factor B (C3 proactivator).

A case of localized heat urticaria is reported in a 51-year-old woman who within a few minutes of contact with warm water developed erythema and swelling sharply localized to the heated area. After a hot bath urticarial lesions appeared over large areas of her body, accompanied by a feeling of weakness, but no other systemic symptoms. After challenge with heat by immersing her left arm in water heated to 42 degrees C, a rapid decrease of her serum complement level of factor B was demonstrated, suggesting that activation of an alternative complement pathway plays a role in this form of urticaria. Biopsies for immunofluorescent study of complement and immunoglobulins were negative at 30 and 180 min after heat challenge. The dermal fibres and endothelial cells of dermal vessels were capable, in vitro, of complement binding before and after exposure to heat.

Complement Factor B↗
PubMed1988

Sequence polymorphism of human complement factor H.

Factor H is a major regulatory protein of the complement system. The complete cDNA coding sequence has been derived from overlapping clones, and a polymorphism at base 1277 has been characterized. In four clones there is a T at nucleotide 1277 and in two others there is a C. This T/C change represents a tyrosine/histidine polymorphism at position 384 in the derived amino acid sequence. Protein sequence studies on peptides generated by trypsin digestion of factor H, purified from pooled plasma from 12 donors, confirmed the presence of both tyrosine and histidine at this position. Tyrosine and histidine were observed in a ratio of 2:1, respectively, and therefore this polymorphism is likely to represent a sequence difference between the two most abundant charge variants, FH1 and FH2, of factor H.

Amino Acid Sequence↗
PubMed1986

Human complement factor H: isolation of cDNA clones and partial cDNA sequence of the 38-kDa tryptic fragment containing the binding site for C3b.

We isolated cDNA clones coding for the functionally important tryptic N-terminal 38-kDa fragment of human complement control protein factor H using polyclonal and monoclonal antibodies to screen a human liver cDNA library cloned in a bacterial expression vector, PEX-1. By testing the reactivity of antibodies specific for the recombinant proteins produced by individual clones with proteolytic fragments of serum H the exact position of these cDNA clones within H was mapped. One clone, H-19, coding for the 38-kDa fragment of H was sequenced and found to code for 289 amino acids derived from the 38-kDa N-terminal fragment as well as for the first 108 amino acids belonging to the complementary 142-kDa tryptic fragment. The derived protein sequence could be arranged in 6 highly homologous repeats of about 60 amino acids each, the homology between the repeats being determined by the characteristic position of cysteine, proline, glycine, tyrosine and tryptophane residues. The region coding for the epitope recognized by one of our monoclonal antibodies was localized by subcloning restriction fragments of H-19 into the expression plasmid and testing for the expression of this epitope.

Amino Acid Sequence↗