Conservation of mechanism, variation of rate: folding kinetics of three homologous four-helix bundle proteins.
The amino acid sequence of a protein determines both its final folded structure and the folding mechanism by which this structure is attained. The differences in folding behaviour between homologous proteins provide direct insights into the factors that influence both thermodynamic and kinetic properties. Here, we present a comprehensive thermodynamic and kinetic analysis of three homologous homodimeric four-helix bundle proteins. Previous studies with one member of this family, Rop, revealed that both its folding and unfolding behaviour were interesting and unusual: Rop folds (k(0)(f) = 29 s(-1)) and unfolds (k(0)(u) = 6 x 10(-7) s(-1)) extremely slowly for a protein of its size that contains neither prolines nor disulphides in its folded structure. The homologues we discuss have significantly different stabilities and rates of folding and unfolding. However, the rate of protein folding directly correlates with stability for these homologous proteins: proteins with higher stability fold faster. Moreover, in spite of possessing differing thermodynamic and kinetic properties, the proteins all share a similar folding and unfolding mechanism. We discuss the properties of these naturally occurring Rop homologues in relation to previously characterized designed variants of Rop.
Dalal
Seema
S
Department of Chemistry, Yale University, New Haven, CT 06520-8114, USA.
Canet
Denis
D
Kaiser
Stephen E
SE
Dobson
Christopher M
CM
Regan
Lynne
L
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry; D001665:Binding Sites; D019791:Guanidine / Q000494:pharmacology; D007700:Kinetics; D008969:Molecular Sequence Data; D017510:Protein Folding; D017433:Protein Structure, Secondary; D016601:RNA-Binding Proteins / Q000737:chemistry; D013816:Thermodynamics
D001426:Bacterial Proteins; D016601:RNA-Binding Proteins; C054243:Rop protein, ColE1 plasmid; D019791:Guanidine