Activation of the fourth component of complement (C4) by C1s results in the generation of a reactive acyl group, able to react with putrescine, and in the release of a free thiol group that cannot be detected in the native haemolytically active molecule. Both the reactive acyl group and the free thiol group have been shown to reside in C4d, a fragment of the alpha′-chain of C4b derived from digestion of the molecule with the control proteins C3b inactivator and C4-binding protein. Peptides derived from CNBr digestion of [1,4-14C]putrescine-labelled and iodo(2-14C]acetic acid-labelled C4d have been obtained and used to establish a continuous sequence of 88 residues from the N-terminus of the molecule. The thiol and reactive acyl groups are contained in an octapeptide that shows near identity with the equivalent sequences reported for alpha 2-macroglobulin and C3. Other adjacent short sections also show homology of sequence between the three proteins, and it is highly likely that they contribute to the overall structure that gives a unique reactivity to the thiol ester bond postulated to exist in the native forms of the three proteins.
Research Article| November 01 1981
Amino acid sequence around the thiol and reactive acyl groups of human complement component C4
Biochem J (1981) 199 (2): 359–370.
- Views Icon Views
- Share Icon Share
- Cite Icon Cite
R D Campbell, J Gagnon, R R Porter; Amino acid sequence around the thiol and reactive acyl groups of human complement component C4. Biochem J 1 November 1981; 199 (2): 359–370. doi: https://doi.org/10.1042/bj1990359
Download citation file: