Functional insights from the structure of the multifunctional C345C domain of C5 of complement.
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The complement protein C5 initiates assembly of the membrane attack complex. This remarkable process results in lysis of target cells and is fundamental to mammalian defense against infection. The 150-amino acid residue domain at the C terminus of C5 (C5-C345C) is pivotal to C5 function. It interacts with enzymes that convert C5 to C5b, the first step in the assembly of the membrane attack complex; it also binds to the membrane attack complex components C6 and C7 with high affinity. Here a recombinant version of this C5-C345C domain is shown to adopt the oligosaccharide/oligonucleotide binding fold, with two helices packed against a five-stranded beta-barrel. The structure is compared with those from the netrin-like module family that have a similar fold. Residues critical to the interaction with C5-convertase cluster on a mobile, hydrophobic inter-strand loop that protrudes from the open face of the beta-barrel. The opposite, helix-dominated face of C5-C345C carries a pair of exposed hydrophobic side chains adjacent to a striking negatively charged patch, consistent with affinity for positively charged factor I modules in C6 and C7. Modeling of homologous domains from complement proteins C3 and C4, which do not participate in membrane attack complex assembly, suggests that this provisionally identified C6/C7-interacting face is indeed specific to C5. (+info)
Two novel mutations in the C7 gene in a Korean patient with complement C7 deficiency.
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Complement C7 deficiency is an autosomal recessive disorder well known to be associated with increased susceptibility to meningococcal infection and has mostly been reported in Caucasians. In the Korean population, no case of C7 deficiency has been reported to date. Recently we experienced an 11-yr-old girl with meningococcal meningitis who was diagnosed as having C7 deficiency based upon the undetectable serum C7 protein on radial immunodiffusion and the undetectable serum total and C7 hemolytic activities. To identify the genetic basis of the C7 deficiency of the patient, we performed a mutation analysis for the C7 gene and found two novel mutations; a point mutation at the 3' splice acceptor site of intron 4 (c.281-1G>T) and a large deletion mutation encompassing almost the whole C7 gene from exon 1 to exon 17 (c.1-?_2350+?del). A haplotype analysis showed that the large deletion mutation was inherited from the patient's father. To the best of our knowledge, this is the first confirmed case of C7 deficiency in Korea. (+info)
Recombinant C345C and factor I modules of complement components C5 and C7 inhibit C7 incorporation into the complement membrane attack complex.
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Complement component C5 binds to components C6 and C7 in reversible reactions that are distinct from the essentially nonreversible associations that form during assembly of the complement membrane attack complex (MAC). We previously reported that the approximately 150-aa residue C345C domain (also known as NTR) of C5 mediates these reversible reactions, and that the corresponding recombinant module (rC5-C345C) binds directly to the tandem pair of approximately 75-residue factor I modules from C7 (C7-FIMs). We suggested from these and other observations that binding of the C345C module of C5 to the FIMs of C7, but not C6, is also essential for MAC assembly itself. The present report describes a novel method for assembling a complex that appears to closely resemble the MAC on the sensor chip of a surface plasmon resonance instrument using the complement-reactive lysis mechanism. This method provides the ability to monitor individually the incorporation of C7, C8, and C9 into the complex. Using this method, we found that C7 binds to surface-bound C5b,6 with a K(d) of approximately 3 pM, and that micromolar concentrations of either rC5-C345C or rC7-FIMs inhibit this early step in MAC formation. We also found that similar concentrations of either module inhibited complement-mediated erythrocyte lysis by both the reactive lysis and classical pathway mechanisms. These results demonstrate that the interaction between the C345C domain of C5 and the FIMs of C7, which mediates reversible binding of C5 to C7 in solution, also plays an essential role in MAC formation and complement lytic activity. (+info)
FcgammaRIIIb and complement component C7 codeficiency in a patient with recurrence of fulminant meningococcal septic shock.
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Individuals with deficiencies of the late components of complement exhibit a susceptibility to the recurrence of meningococcal disease with a usually mild clinical presentation. We report the recurrence of fulminant meningococcal disease in a complement component C7-deficient patient. We found a total deficiency of FcgammaRIIIb on neutrophils, which could partially explain the unusually severe clinical presentation. (+info)
Molecular defects of the C7 gene in two patients with complement C7 deficiency.
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Different genetic mutations have been described in complement components resulting in total or subtotal deficiency states. In this work we report the genetic basis of C7 deficiency in a previously reported Spanish patient exhibiting a combined total deficiency of C7 and C4B associated with systemic lupus erythematosus. Exon-specific polymerase chain reaction and sequencing revealed a not previously described single base mutation in exon 10 (T1458A) leading to a stop codon that causes the premature truncation of the C7 protein (C464X). Additionally, a C to A transversion at position 1561 (exon 11) was found in the patient resulting in an amino acid change (R499S). This latter mutation has been previously reported in individuals with subtotal C7 deficiency or with combined subtotal C6/C7 deficiency from widely spaced geographical areas. Another novel mutation was found in a second patient with meningococcal meningitis of Bolivian and Czech origin; a 11-base pair deletion of nucleotides 631-641 in exon 6 leading to the generation of a downstream stop codon causing the premature truncation of the C7 protein product (T189 x 193). This patient was found to be a heterozygous compound for another mutation in C7; a two-base pair deletion of nucleotides 1922 and 1923, 1923 and 1924 or 1924 and 1925 in exon 14 (1922delAG/1923delGA/1924delAG), leading again to the generation of a downstream stop codon that provokes the truncation of the C7 protein (S620x630). This latter mutation has been recently reported by our group in another Spanish family. Our results provide more evidences for the heterogeneous molecular basis of C7 deficiency. (+info)
C7 is expressed on endothelial cells as a trap for the assembling terminal complement complex and may exert anti-inflammatory function.
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