Contrasting roles for symmetrically disposed beta-turns in the folding of a small protein

TitleContrasting roles for symmetrically disposed beta-turns in the folding of a small protein
Publication TypeJournal Article
Year of Publication1997
AuthorsGu, H., Kim D. E., & Baker D.
JournalJournal of molecular biology
Volume274
Issue4
Pagination588-96
Date Published1997 Dec 12
ISSN0022-2836
KeywordsBacterial Proteins, Bacteriophages, Base Sequence, Models, Molecular, Molecular Sequence Data, Mutagenesis, Mutation, Point Mutation, Primary Publication, Protein Folding
Abstract

To investigate the role of turns in protein folding, we have characterized the effects of combinatorial and site-directed mutations in the two beta-turns of peptostreptococcal protein L on folding thermodynamics and kinetics. Sequences of folded variants recovered from combinatorial libraries using a phase display selection method were considerably more variable in the second turn than in the first turn. These combinatorial mutants as well as strategically placed point mutants in the two turns had a similar range of thermodynamic stabilities, but strikingly different folding kinetics. A glycine to alanine substitution in the second beta-turn increased the rate of unfolding more than tenfold but had little effect on the rate of folding, while mutation of a symmetrically disposed glycine residue in the first turn had little effect on unfolding but slowed the rate of folding nearly tenfold. These results demonstrate that the role of beta-turns in protein folding is strongly context-dependent, and suggests that the first turn is formed and the second turn disrupted in the folding transition state.

Alternate JournalJ. Mol. Biol.
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