The chloroplast‐targeting domain of plastocyanin transit peptide can form a helical structure but does not have a high affinity for lipid bilayers

Abstract

Conformational properties and interactions with lipid membranes were studied for the chemically synthesized peptides PC(1–37) and PC(1–43), corresponding to the N‐terminal 37 and 43 residues, respectively, of the transit peptide of the precursor to plastocyanin of Silene pratensis. PC(1–43) covers the entire chloroplast targeting domain of the transit peptide. CD spectra of PC(1–37) and PC(1–43) showed that both peptides have little ordered structure in aqueous solutions but form partially helical conformations in the presence of detergent micelles or in methanol. Vesicle disruption and direct‐binding experiments revealed, however, that neither PC(1–37) nor PC(1–43) had a high affinity for lipid membranes. Since in the intact plastocyanin transit peptide the chloroplast‐targeting domain is followed by a hydrophobic thylakoid‐transfer domain, the plastopcyanin precursor may well be transported to the chloroplast surface first with the aid of the thylakoid‐transfer domain. The chloroplast‐targeting domain may then form a helical structure in the lipid environments, and a chloroplast‐specific motif displayed on the helical structure may be recognized by a receptor protein located at the chloroplast envelope membranes. Copyright © 1992, Wiley Blackwell. All rights reserved