tailieunhanh - Báo cáo khoa học: An Escherichia coli twin-arginine signal peptide switches between helical and unstructured conformations depending on the hydrophobicity of the environment

The Tat system catalyzes the transport of folded globular proteins across the bacterial plasma membrane and the chloroplast thylakoid. It recognizes cleavable signal peptides containingacritical twin-argininemotif but little isknownof the overall structure of these peptides. In this report, we have analyzed the secondary structure of the SufI signal peptide, together with those of two nonfunctional variants in which the region around the twin-arginine, RRQFI, is replaced by KKQFI or RRQAA. Circular dichroism studies show that the SufI peptide exists as anunstructuredpeptide in aqueous solvent with essentially no stable secondary structure | Eur. J. Biochem. 270 3345-3352 2003 FEBS 2003 doi An Escherichia coli twin-arginine signal peptide switches between helical and unstructured conformations depending on the hydrophobicity of the environment Miguel San Miguel1 Rachel Marrington2 P. Mark Rodger2 Alison Rodger2 and Colin Robinson 1 Department of Biological Sciences and department of Chemistry University of Warwick Coventry UK The Tat system catalyzes the transport of folded globular proteins across the bacterial plasma membrane and the chloroplast thylakoid. It recognizes cleavable signal peptides containing a critical twin-arginine motif but little is known of the overall structure of these peptides. In this report we have analyzed the secondary structure of the SufI signal peptide together with those of two nonfunctional variants in which the region around the twin-arginine RRQFI is replaced by KKQFI or RRQAA. Circular dichroism studies show that the SufI peptide exists as an unstructured peptide in aqueous solvent with essentially no stable secondary structure. In membrane-mimetic environments such as SDS micelles or water trifluoroethanol however the peptide adopts a structure containing up to about 40 a-helical content. Secondary structure predictions and molecular modelling programs strongly suggest that the helical region begins at or close to the twin-arginine motif. Studies on the thermal stability of the helix demonstrate a sharp transition between the unstructured and helical states suggesting that the peptide exists in one of two distinct states. The two nonfunctional peptides exhibit almost identical spectra and properties to the wild-type SufI peptide indicating that it is the arginine sidechains and not their contribution to the helical structure that are critical in this class of peptide. Keywords signal peptide twin-arginine translocation Tat system protein transport SufI. The twin-arginine translocation Tat system operates in the cytoplasmic membranes

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