Figure 1.

Alkylation pattern of Lhcb₅ in the cpSRP43·Lhcb₅ complex show cpSRP43-induced protection on the substrate protein. A and B, mass spectrum (upper left), deconvolution (lower panels), and component analysis (upper right) for a partially alkylated Lhcb₅ residue, Cys-135 (A) and a completely alkylated Lhcb₅ residue, Cys-156 (B). C, summary of the NEM alkylation efficiencies at individual sites in Lhcb₅. Alkylation reactions were carried out for 10 min. For each engineered cysteine, “fraction accessible” was calculated from the ratio of the fraction of alkylation in the cpSRP43·Lhcb₅ complex relative to that of Lhcb₅ dissolved in 6 m GdmHCl. Error bars indicate S.E., with n = 2. D, the alkylation protection pattern of Lhcb₅ in complex with cpSRP43 is mapped onto the sequence of Lhcb₅. Colored triangles denote the extent of protection, with white denoting the least protection (0% protection, or 100% alkylation) and blue denoting the highest observed protection (>50% protection or <50% alkylation).