Structural homology of complement protein C6 with other channel-forming proteins of complement.
The amino acid sequence of the amino-terminal half of the complement protein C6 has been found to show overall structural homology with the homologous regions of the channel-forming proteins C7, C8 alpha, C8 beta, and C9. In addition, two specific cysteine-rich segments common to the amino-terminal regions of C7, C8 alpha, C8 beta, and C9 also occur in their expected positions in C6, suggesting functional significance. Two cDNA clones encoding C6 were isolated from a human liver library in the bacteriophage vector lambda gt11. The predicted protein sequence contains an apparent initiation methionine and a putative signal peptide of 21 residues, as well as a site for N-glycosylation at residue 303. The sequence of the C6 protein reported here has 47-52% similarity with C7, C8 alpha, C8 beta, and C9, as well as 31-38% similarity with thrombospondin, thrombomodulin, and low density lipoprotein receptor. The sequence data have been interpreted by using computer algorithms for estimation of average hydrophobicity and secondary structure.
Chakravarti
D N
DN
Department of Immunology, Research Institute of Scripps Clinic, La Jolla, CA 92037.
Chakravarti
B
B
Parra
C A
CA
Muller-Eberhard
H J
HJ
D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D003183:Complement C6 / Q000648:ultrastructure*; D015938:Complement Membrane Attack Complex; D003165:Complement System Proteins / Q000235:genetics*; D003545:Cysteine; D004247:DNA / Q000235:genetics; D006801:Humans; D007473:Ion Channels / Q000648:ultrastructure*; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins / Q000648:ultrastructure; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D012995:Solubility
D003183:Complement C6; D015938:Complement Membrane Attack Complex; D007473:Ion Channels; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins; D003165:Complement System Proteins; D004247:DNA; D003545:Cysteine