The Trp-cage: optimizing the stability of a globular miniprotein.
The Trp-cage, as the smallest miniprotein, remains the subject of numerous computational and experimental studies of protein folding dynamics and pathways. The original Trp-cage (NLYIQWLKDGGPSSGRPPPS, Tm = 42 degrees C) can be significantly stabilized by mutations; melting points as high as 64 degrees C are reported. In helical portions of the structure, each allowed replacement of Leu, Ile, Lys or Ser residues by Ala results in a 1.5 (+/-0.35) kJ/mol fold stabilization. No changes in structure or fluxionality of the core results upon stabilization. Contrary to the initial hypothesis, specific Pro/Trp interactions are not essential for core formation. The entropic advantage of Pro versus Ala (DeltaDeltaS(U) = 11 +/- 2 J/mol K) was measured at the solvent-exposed P17 site. Pro-Ala mutations at two of the three prolines (P12 and P18) that encage the indole ring result in less fold destabilization (2.3-3.4 kJ/mol). However, a P19A mutation reduces fold stability by 16 kJ/mol reflecting a favorable Y3/P19 interaction as well as Trp burial. The Y3/P19 hydrophobic staple interaction defines the folding motif as an 18-residue unit. Other stabilizing features that have been identified include a solvent-exposed Arg/Asp salt bridge (3.4-6 kJ/mol) and a buried H-bonded Ser side chain ( approximately 10 kJ/mol).
Barua
Bipasha
B
Department of Chemistry, University of Washington, Seattle, WA 98195, USA.
Lin
Jasper C
JC
Williams
Victoria D
VD
Kummler
Phillip
P
Neidigh
Jonathan W
JW
Andersen
Niels H
NH
D000595:Amino Acid Sequence; D002942:Circular Dichroism; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008969:Molecular Sequence Data; D011392:Proline / Q000737:chemistry; D017510:Protein Folding; D017433:Protein Structure, Secondary; D013816:Thermodynamics; D014364:Tryptophan / Q000737:chemistry*; D014443:Tyrosine / Q000737:chemistry
D014443:Tyrosine; D014364:Tryptophan; D011392:Proline