Contribution of Thr29 to the thermodynamic stability of goat alpha-lactalbumin as determined by experimental and theoretical approaches.Horii, K., Saito, M., Yoda, T., Tsumoto, K., Matsushima, M., Kuwajima, K., Kumagai, I.
(2001) Proteins 45: 16-29
- PubMed: 11536356
- Primary Citation of Related Structures:
- PubMed Abstract:
- Effect of the extra N-terminal Methionine residue on the stability and folding of recombinant alpha-lactalbumin expressed in Escherichia coli
Chaudhuri, T.K.,Horii, K.,Yoda, T.,Arai, M.,Nagata, S.,Terada, T.P.,Uchiyama, H.,Ikura, T.,Tsumoto, K.,Kataoka, H.,Matsushima, M.,Kuwajima, K.,Kumagai, I.
(1999) J.Mol.Biol. 285: 1179
The Thr29 residue in the hydrophobic core of goat alpha-lactalbumin (alpha-LA) was substituted with Val (Thr29Val) and Ile (Thr29Ile) to investigate the contribution of Thr29 to the thermodynamic stability of the protein. We carried out protein stabi ...
The Thr29 residue in the hydrophobic core of goat alpha-lactalbumin (alpha-LA) was substituted with Val (Thr29Val) and Ile (Thr29Ile) to investigate the contribution of Thr29 to the thermodynamic stability of the protein. We carried out protein stability measurements, X-ray crystallographic analyses, and free energy calculations based on molecular dynamics simulation. The equilibrium unfolding transitions induced by guanidine hydrochloride demonstrated that the Thr29Val and Thr29Ile mutants were, respectively, 1.9 and 3.2 kcal/mol more stable than the wild-type protein (WT). The overall structures of the mutants were almost identical to that of WT, in spite of the disruption of the hydrogen bonding between the side-chain O-H group of Thr29 and the main-chain C=O group of Glu25. To analyze the stabilization mechanism of the mutants, we performed free energy calculations. The calculated free energy differences were in good agreement with the experimental values. The stabilization of the mutants was mainly caused by solvation loss in the denatured state. Furthermore, the O-H group of Thr29 favorably interacts with the C=O group of Glu25 to form hydrogen bonds and, simultaneously, unfavorably interacts electrostatically with the main-chain C=O group of Thr29. The difference in the free energy profile of the unfolding path between WT and the Thr29Ile mutant is discussed in light of our experimental and theoretical results.
Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Sendai, Japan.