Kinetic Stabilization of Bacillus Licheniformis Alpha-Amylase Through Introduction of Hydrophobic Residues at the SurfaceMachius, M., Declerck, N., Huber, R., Wiegand, G.
(2003) J.Biol.Chem. 278: 11546
- PubMed: 12540849
- DOI: 10.1074/jbc.M212618200
- PubMed Abstract:
- Activation of Bacillus Licheniformis Alpha-Amylase Through a Disorder-->Order Transition of the Substrate-Binding Site Mediated by a Calcium-Sodium-Calcium Metal Triad
Machius, M.,Declerck, N.,Huber, R.,Wiegand, G.
(1998) Structure 6: 281
- Crystal Structure of Calcium-Depleted Bacillus Licheniformis Alpha-Amylase at 2.2 A Resolution
Machius, M.,Wiegand, G.,Huber, R.
(1995) J.Mol.Biol. 246: 545
- Crystal Structure of Thermostable Alpha-Amylase from Bacillus Licheniformis Refined at 1.7 A Resolution
Hwang, K.Y.,Song, H.K.,Chang, C.,Lee, J.,Lee, S.Y.,Kim, K.K.,Choe, S.,Sweet, R.M.,Suh, S.W.
(1997) Mol.Cells 7: 251
It is generally assumed that in proteins hydrophobic residues are not favorable at solvent-exposed sites, and that amino acid substitutions on the surface have little effect on protein thermostability. Contrary to these assumptions, we have identifie ...
It is generally assumed that in proteins hydrophobic residues are not favorable at solvent-exposed sites, and that amino acid substitutions on the surface have little effect on protein thermostability. Contrary to these assumptions, we have identified hyperthermostable variants of Bacillus licheniformis alpha-amylase (BLA) that result from the incorporation of hydrophobic residues at the surface. Under highly destabilizing conditions, a variant combining five stabilizing mutations unfolds 32 times more slowly and at a temperature 13 degrees C higher than the wild-type. Crystal structure analysis at 1.7 A resolution suggests that stabilization is achieved through (a) extension of the concept of increased hydrophobic packing, usually applied to cavities, to surface indentations, (b) introduction of favorable aromatic-aromatic interactions on the surface, (c) specific stabilization of intrinsic metal binding sites, and (d) stabilization of a beta-sheet by introducing a residue with high beta-sheet forming propensity. All mutated residues are involved in forming complex, cooperative interaction networks that extend from the interior of the protein to its surface and which may therefore constitute "weak points" where BLA unfolding is initiated. This might explain the unexpectedly large effect induced by some of the substitutions on the kinetic stability of BLA. Our study shows that substantial protein stabilization can be achieved by stabilizing surface positions that participate in underlying cooperatively formed substructures. At such positions, even the apparently thermodynamically unfavorable introduction of hydrophobic residues should be explored.
University of Texas, Southwestern Medical Center at Dallas, Texas 75390, USA. Mischa.Machius@UTSouthwestern.edu