Time resolution of binding and membrane insertion of a mitochondrial signal peptide: correlation with structural changes and evidence for cooperativity.

Utilizing a recently developed novel fluorescence technique [Wall et al. (1995) Mol. Membr. Biol. 12, 183-192], it is shown that the interactions of p25, the leader peptide of subunit IV of cytochrome c oxidase, with phospholipid membranes can be identified in real time. p25 is observed to bind following stopped-flow mixing of the peptide with phospholipid membranes with rate constants up to about 700 s-1 and then insert into the membrane with rate constants on the order of 0.4 s-1. Comparison of these processes with similarly time-resolved experiments performed with a stopped-flow CD spectrometer revealed that p25 does not become alpha-helical upon binding to the membrane. Following membrane insertion, however, p25 was observed to adopt an alpha-helical configuration. The temperature dependency of these processes was then found to yield activation energies for the respective components of the p25-membrane interaction.