Amino acid sequence homologies and glycosylation differences between the fourth component of murine complement and sex-limited protein.

Abstract

Limited primary sequence data were obtained for all 3 subunits of the 4th component of murine complement (C4) and its related homolog, the sex-limited protein (Slp). These data show a high degree of NH2-terminal homology between C4 and Slp: 4 of the 6 residues identified for the .alpha. chain, 7 of 8 for the .beta. chain, and 4 of 4 for the .gamma. chain. This suggests that apparent MW differences between C4 and Slp subunits are not, as previously suggested, due to a shift in the proteolytic processing sites in the pro-Slp polypeptide molecule. Chemical deglycosylation (apparently complete) of the C4 and Slp .alpha. chains with trifluoromethanesulfonic acid removes the MW difference between them, suggesting that acquisition of extra glycosylation sites in the latter is responsible for this difference.