Identification of the preprotein binding domain of SecA

Efrosyni Papanikou, Spyridoula Karamanou, Catherine Baud, Miriam Frank, Giorgos Sianidis, Dimitra Keramisanou, Charalampos G. Kalodimos, Andreas Kuhn, Anastassios Economou

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74 Scopus citations


SecA, the preprotein translocase ATPase, has a helicase DEAD motor. To catalyze protein translocation, SecA possesses two additional flexible domains absent from other helicases. Here we demonstrate that one of these "specificity domains" is a preprotein binding domain (PBD). PBD is essential for viability and protein translocation. PBD mutations do not abrogate the basal enzymatic properties of SecA (nucleotide binding and hydrolysis), nor do they prevent SecA binding to the SecYEG protein conducting channel. However, SecA PBD mutants fail to load preproteins onto SecYEG, and their translocation ATPase activity does not become stimulated by preproteins. Bulb and Stem, the two sterically proximal PBD substructures, are physically separable and have distinct roles. Stem binds signal peptides, whereas the Bulb binds mature preprotein regions as short as 25 amino acids. Binding of signal or mature region peptides or full-length preproteins causes distinct conformational changes to PBD and to the DEAD motor. We propose that (a) PBD is a preprotein receptor and a physical bridge connecting bound preproteins to the DEAD motor, and (b) preproteins control the ATPase cycle via PBD.

Original languageEnglish (US)
Pages (from-to)43209-43217
Number of pages9
JournalJournal of Biological Chemistry
Issue number52
StatePublished - Dec 30 2005


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