The high affinity ATP binding site modulates the SecA-precursor interaction

SecA is the central component of the protein-translocation machinery of Esc herichia coli, It is able to interact with the precursor protein, the chape rone SecB, the integral membrane protein complex SecYEG, acidic phospholipi ds and its own mRNA, We studied the interaction between prePhoE and SecA by using a site-specific photocrosslinking strategy. We found that SecA is ab le to interact with both the signal sequence and the mature domain of prePh oE, Furthermore, this interaction was dependent on the type of nucleotide b ound. SecA in the ADP-bound conformation was unable to crosslink with the p recursor, whereas the ATP-bound conformation was active in precursor crossl inking, The SecA-precursor interaction was maintained in the presence of E. coli phospholipids but was loosened by the presence of phosphatidylglycero l bilayers, Examining SecA ATP binding site mutants demonstrated that ATP h ydrolysis at the N-terminal high affinity binding site is responsible for t he changed interaction with the preprotein. (C) 2000 Federation of European Biochemical Societies, Published by Elsevier Science B,V, All rights reser ved.