    1.2.5.1 | more |
systematical substitution of cysteine at 18 amino acid positions within the C-terminal region to obtain a panel of proteins each having a single residue changed to cysteine. In the absence of pyruvate, the cysteine residues of the modified PoxB proteins fail to form disulfide bonds, generally fail to react with a large and rigid hydrophilic sulfhydryl reagent, 4-acetamido-4'-[(iodoacetyl)amino]stilbene-2,2'-disulfonic acid (IASD), and in some cases react weakly with a smaller more hydrophobic reagent, N-ethylmaleimide. In this conformation, the C termini appear fixed in a rigid environment having limited exposure to solvent. In the presence of pyruvate, all of the C-terminal cysteine residues, except the two most distal from the C terminus, react with both sulfhydryl reagents and readily formed disulfide cross-linked species. In the presence of lipid activators, Triton X-100 or dipalmitoylphosphatidylglycerol, a subset of the cysteine-substituted proteins no longer reacts with the membrane-impermeable IASD reagent, indicating penetration of these protein segments into the lipid micelle |
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