• Application of the substituted cysteine accessibility method (SCAM) to LacY, the lactose permease, demonstrates that SCAM is a powerful tool for structural and functional studies of membrane transporters. • SCAM, combined with cysteine-scanning mutagenesis, reveals functionally important amino residues in LacY. • Site-directed alkylation of single-cysteine replacements provides insights into the conformational dynamics of LacY and supports the alternating-access mechanism. • Site-directed cysteine cross-linking studies establish a helix-packing model of LacY in the absence of a crystal structure.
Jiang et al. (Fri,) studied this question.