Bacillus subtilisFfh, A Homologue of Mammalian SRP54, Can Intrinsically Bind to the Precursors of Secretory Proteins

Abstract

We analyzed the binding activity ofB. subtilisFfh to the precursors of secretory proteins by purifying mature and precursor proteins of β-lactamase derived from pUC18 and its derivatives, of which the signal peptide region was replaced with that ofE. coliOmpA,B. subtilisAprE, PBP5* or an alkalophilicBacillus sp.#1011 CGTase. Each of them was mixed with purifiedB. subtilisFfh in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDAC). The tested precursor proteins, including those ofE. coli,of which the signal sequences differ from those ofB. subtilisin the number of charged amino acids and hydrophobicity, cross-linked with Ffh, whereas mature proteins did not. The addition of scRNA, theB. subtiliscounterpart of mammalian SRP 7S RNA, into the mixture did not affect the complex formation. These findings suggest thatB. subtilisFfh intrinsically binds to several precursor proteins.