PMID:12423355
| Citation |
Adams, H, Scotti, PA, De Cock, H, Luirink, J and Tommassen, J (2002) 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. Eur. J. Biochem. 269:5564-71 |
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| Abstract |
Signal sequences often contain alpha-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 alpha-helix. Previously, we showed that substitution of Gly-10 by alpha-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 considered the possibility that extension of the alpha-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 P48, 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, the targeting pathway that is exploited by integral inner-membrane proteins. Together, these data indicate that the helix breaker in cleavable signal sequences prevents recognition by SRP and is thereby, together with the hydrophobicity of the signal sequence, a determinant of the targeting pathway. |
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| Keywords |
Amino Acid Sequence; Escherichia coli/genetics; Escherichia coli/metabolism; Escherichia coli Proteins; Glycine/chemistry; Kinetics; Molecular Sequence Data; Mutation; Plasmids/metabolism; Porins/chemistry; Porins/metabolism; Protein Biosynthesis; Protein Structure, Secondary; Protein Structure, Tertiary; Signal Recognition Particle; Time Factors; Transcription, Genetic |
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