Locations of the six disulphide bonds in a variant surface glycoprotein (VSG 117) from Trypanosoma brucei.

The locations of the six disulphide bonds and the single free cysteine residue in a variant surface glycoprotein, VSG 117, from the African trypanosome Trypanosoma brucei have been determined to be Cys-14--Cys-140, Cys-121--Cys-182, Cys-389--Cys-404, Cys-398--417, Cys-447--Cys-461 and Cys-455--Cys-468. Cys-244 bears the single thiol group, which is unreactive towards 2-nitro-5-thiocyanobenzoate in the native molecule and is probably buried. Biosynthetically incorporated [35S]cysteine aided the location of the disulphide bonds. Two proteinase-resistant glycosylated domains, each containing two disulphide bonds, were identified in the C-terminal region of the glycoprotein. Details of purification of [35S]cysteine-containing peptides, and Tables of amino acid analyses, are presented in Supplementary Publication SUP 50119 (32 pages), which has been deposited with the British Library Lending Division, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1981) 193,5.