TAILIEUCHUNG - Báo cáo Y học: The presence of a helix breaker in the hydrophobic core of signal sequences of secretory proteins prevents recognition by the signal-recognition particle in Escherichia coli

Signal sequences often containa-helix-destabilizing amino acids within the hydrophobic core. In the precursor of the Escherichia coliouter-membrane protein PhoE,the glycine residue at position)10 (Gly )10 ) is thought to be responsible for the break in the a-helix. Previously,we showed that substitution of Gly )10 bya-helix-promoting residues (Ala, Cys or Leu) reduced the proton-motive force dependency of the translocation of the precursor,but the actual role of the helix breaker remained obscure. . | Eur. J. Biochem. 269 5564-5571 2002 FEBS 2002 doi The presence of a helix breaker in the hydrophobic core of signal sequences of secretory proteins prevents recognition by the signal-recognition particle in Escherichia coli Hendrik Adams1 Pier A. Scotti2 Hans de Cock1 Joen Luirink2 and Jan Tommassen1 1 Department of Molecular Microbiology and Institute of Biomembranes Utrecht University The Netherlands department of Microbiology Institute of Molecular Biological Sciences Biocentrum Amsterdam The Netherlands Signal sequences often contain a-helix-destabilizing amino acids within the hydrophobic core. In the precursor of the Escherichia coli outer-membrane protein PhoE the glycine residue at position -10 Gly-10 is thought to be responsible for the break in the a-helix. Previously we tliowed tliat substitution of Gly-10 by a-helix-promoting residues Ala Cys or Leu reduced the proton-motive force dependency of the translocation of the precursor but the actual role of the helix breaker remained obscure. Here we eonsidered the possibility that extension of the a-helical structure in the signal sequence resulting from the Gly-10 substitutions affects the targeting pathway of the precursor. Indeed the mutations resulted in reduced dependency on SecB for targeting in vivo. In vitro cross-linking experiments revealed that the G-10L and G-10C mutant PhoE precursors had a dramatically increased affinity for P43 one of the constituents of the signal-recognition particle SRP . Furthermore in vitro cross-linking experiments revealed that the G-10L mutant protein is routed to the SecYEG translocon via the SRP pathway die larged ng pathway that is exposed by nt legal 1 inner-membrane proteins. Together these data indicate that the helix breaker in cleavable signal sequences prevents recognition by SRP and is thereby tggetSer with die hydrophobicity of the signal sequence a delermínant of the targeting pathway. Keywords outer-membrane protein Sec .

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