A 100-kDa protein in the C4-activating component of Ra-reactive factor is a new serine protease having module organization similar to C1r and C1s.
Ra-reactive factor (RaRF), a C-dependent bactericidal factor in mice, is composed of one polysaccharide-binding component and one C4/C2-activating component. The former is an oligomer of 28-kDa protein corresponding to the mannose-binding protein of mice. The 100-kDa protein, P100, has been shown to be present in the C4/C2-activating component. This protein generates 29- and 70-kDa polypeptide chains when reduced. In this study, we determined the nucleotide sequence of cDNA coding for P100. cDNAs were prepared by reverse transcription PCR and cassette-ligation-mediated PCR on mRNA from BALB/c mouse liver, using primers synthesized by reference to the sequence determined in a previous study. The results of cDNA sequencing indicate that the precursor protein of P100 containing a 24-residue signal peptide consists of 704 amino acid residues. Taking the results of the previous electrophoretic study into consideration, it is thought that the cleavage of mature P100 protein generates a 29-kDa chain of 251 residues and a 70-kDa chain of 429 residues. Although homology in the amino acid sequence of P100 with that of human C1r and C1s subcomponents of C was less than 40%, a striking similarity in domain organization was found among these proteins, indicating that P100 is a new C4-activating serine protease structurally similar to C1r and C1s. Northern hybridization showed that the liver was the primary site of the expression of the P100 gene.
Takayama
Y
Y
Department of Molecular Biology, School of Medicine, Kitasato University, Kanagawa, Japan.
Takada
F
F
Takahashi
A
A
Kawakami
M
M
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D003167:Complement Activation; D015923:Complement C1r / Q000235:genetics; D003173:Complement C1s / Q000235:genetics; D003181:Complement C4 / Q000378:metabolism*; D006224:Cricetinae; D017931:DNA Primers / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D015870:Gene Expression; D006801:Humans; D050606:Mannose-Binding Protein-Associated Serine Proteases; D051379:Mice; D008813:Mice, Inbred ICR; D008969:Molecular Sequence Data; D008970:Molecular Weight; D012333:RNA, Messenger / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D012697:Serine Endopeptidases / Q000737:chemistry / Q000235:genetics* / Q000276:immunology*
D003181:Complement C4; D017931:DNA Primers; D018076:DNA, Complementary; D012333:RNA, Messenger; C084067:MASP1 protein, human; D050606:Mannose-Binding Protein-Associated Serine Proteases; D012697:Serine Endopeptidases; D015923:Complement C1r; D003173:Complement C1s