Contribution of Hydrophobic Interactions to Protein Stability

• Published in: Journal of molecular biology 2011-05, Vol.408 (3), p.514-528
• Main Authors: Pace, C. Nick, Fu, Hailong, Fryar, Katrina Lee, Landua, John, Trevino, Saul R., Shirley, Bret A., Hendricks, Marsha McNutt, Iimura, Satoshi, Gajiwala, Ketan, Scholtz, J. Martin, Grimsley, Gerald R.
• Format: Article
• Language: English
• Subjects: Antigens, Bacterial - chemistry; Antigens, Bacterial - genetics; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Borrelia burgdorferi; conformational entropy; Entropy; hydrogen bonding; hydrogen bonds; Hydrophobic and Hydrophilic Interactions; hydrophobic bonding; hydrophobic interactions; hydrophobicity; large proteins; Lipoproteins - chemistry; Lipoproteins - genetics; Microfilament Proteins - chemistry; Microfilament Proteins - genetics; mutants; Mutation; Protein Conformation; Protein Stability; Ribonuclease T1 - chemistry; Ribonuclease T1 - genetics; ribonucleases; Ribonucleases - chemistry; Ribonucleases - genetics; small proteins; surface proteins
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1016/j.jmb.2011.02.053

Our goal was to gain a better understanding of the contribution of hydrophobic interactions to protein stability. We measured the change in conformational stability, Δ(Δ G), for hydrophobic mutants of four proteins: villin headpiece subdomain (VHP) with 36 residues, a surface protein from Borrelia burgdorferi (VlsE) with 341 residues, and two proteins previously studied in our laboratory, ribonucleases Sa and T1. We compared our results with those of previous studies and reached the following conclusions: (1) Hydrophobic interactions contribute less to the stability of a small protein, VHP (0.6 ± 0.3 kcal/mol per –CH 2– group), than to the stability of a large protein, VlsE (1.6 ± 0.3 kcal/mol per –CH 2– group). (2) Hydrophobic interactions make the major contribution to the stability of VHP (40 kcal/mol) and the major contributors are (in kilocalories per mole) Phe18 (3.9), Met13 (3.1), Phe7 (2.9), Phe11 (2.7), and Leu21 (2.7). (3) Based on the Δ(Δ G) values for 148 hydrophobic mutants in 13 proteins, burying a –CH 2– group on folding contributes, on average, 1.1 ± 0.5 kcal/mol to protein stability. (4) The experimental Δ(Δ G) values for aliphatic side chains (Ala, Val, Ile, and Leu) are in good agreement with their Δ G tr values from water to cyclohexane. (5) For 22 proteins with 36 to 534 residues, hydrophobic interactions contribute 60 ± 4% and hydrogen bonds contribute 40 ± 4% to protein stability. (6) Conformational entropy contributes about 2.4 kcal/mol per residue to protein instability. The globular conformation of proteins is stabilized predominantly by hydrophobic interactions.