Different members of a simple three-helix bundle protein family have very different folding rate constants and fold by different mechanisms.
The 15th, 16th, and 17th repeats of chicken brain alpha-spectrin (R15, R16, and R17, respectively) are very similar in terms of structure and stability. However, R15 folds and unfolds 3 orders of magnitude faster than R16 and R17. This is unexpected. The rate-limiting transition state for R15 folding is investigated using protein engineering methods (Phi-value analysis) and compared with previously completed analyses of R16 and R17. Characterisation of many mutants suggests that all three proteins have similar complexity in the folding landscape. The early rate-limiting transition states of the three domains are similar in terms of overall structure, but there are significant differences in the patterns of Phi-values. R15 apparently folds via a nucleation-condensation mechanism, which involves concomitant folding and packing of the A- and C-helices, establishing the correct topology. R16 and R17 fold via a more framework-like mechanism, which may impede the search to find the correct packing of the helices, providing a possible explanation for the fast folding of R15.
Wensley
Beth G
BG
Department of Chemistry, MRC Centre for Protein Engineering, University of Cambridge, UK.
Gärtner
Martina
M
Choo
Wan Xian
WX
Batey
Sarah
S
Clarke
Jane
J
D000595:Amino Acid Sequence; D000818:Animals; D002645:Chickens; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D013049:Spectrin / Q000737:chemistry* / Q000378:metabolism*; D013816:Thermodynamics
D050505:Mutant Proteins; D013049:Spectrin