The Trp-cage: optimizing the stability of a globular miniprotein
Open Access
- 18 January 2008
- journal article
- research article
- Published by Oxford University Press (OUP) in Protein Engineering, Design and Selection
- Vol. 21 (3), 171-185
- https://doi.org/10.1093/protein/gzm082
Abstract
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°C) can be significantly stabilized by mutations; melting points as high as 64°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 (ΔΔSU = 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 (≈10 kJ/mol).Keywords
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