Ej. Bures et al., DETERMINATION OF DISULFIDE STRUCTURE IN AGOUTI-RELATED PROTEIN (AGRP)BY STEPWISE REDUCTION AND ALKYLATION, Biochemistry, 37(35), 1998, pp. 12172-12177
The agouti-related protein gene (Agrp) plays an important role in body
weight regulation. The mature human protein is a single polypeptide c
hain of 112 amino acid residues, consisting of an N-terminal acidic re
gion and a unique C-terminal cysteine-rich domain. The disulfide struc
ture of recombinant human AGRP was determined by chemical methods usin
g partial reduction with tris(2-carboxyethyl)phosphine under acidic co
nditions, followed by direct alkylation with N-ethylmaleimide or fluor
escein-5-maleimide. Partial reduction and alkylation provided several
forms of AGRP that were modified in a stepwise fashion. The resulting
proteins were characterized by peptide mapping, sequence analysis, and
mass spectrometry, showing that AGRP contained a highly reducible dis
ulfide bond, C85-C109, followed by less reactive ones, C90-C97, C74-C8
8, C67-C82, and C81-C99, respectively. The chemically defined disulfid
e connectivity of the recombinant human AGRP was homologous to that of
omega-agatoxin IVB except for an additional disulfide bond, C85-C109.