CRYSTAL-STRUCTURE OF RECOMBINANT TRIOSEPHOSPHATE ISOMERASE FROM BACILLUS-STEAROTHERMOPHILUS - AN ANALYSIS OF POTENTIAL THERMOSTABILITY FACTORS IN 6 ISOMERASES WITH KNOWN 3-DIMENSIONAL STRUCTURES POINTS TO THE IMPORTANCE OF HYDROPHOBIC INTERACTIONS

Citation
Lf. Delboni et al., CRYSTAL-STRUCTURE OF RECOMBINANT TRIOSEPHOSPHATE ISOMERASE FROM BACILLUS-STEAROTHERMOPHILUS - AN ANALYSIS OF POTENTIAL THERMOSTABILITY FACTORS IN 6 ISOMERASES WITH KNOWN 3-DIMENSIONAL STRUCTURES POINTS TO THE IMPORTANCE OF HYDROPHOBIC INTERACTIONS, Protein science, 4(12), 1995, pp. 2594-2604
Citations number
77
Categorie Soggetti
Biology
Journal title
ISSN journal
09618368
Volume
4
Issue
12
Year of publication
1995
Pages
2594 - 2604
Database
ISI
SICI code
0961-8368(1995)4:12<2594:CORTIF>2.0.ZU;2-2
Abstract
The structure of the thermostable triosephosphate isomerase (TIM) from Bacillus stearothermophilus complexed with the competitive inhibitor 2-phosphoglycolate was determined by X-ray crystallography to a resolu tion of 2.8 Angstrom. The structure was solved by molecular replacemen t using XPLOR. Twofold averaging and solvent flattening was applied to improve the quality of the map. Active sites in both the subunits are occupied by the inhibitor and the flexible loop adopts the ''closed'' conformation in either subunit. The crystallographic R-factor is 17.6 % with good geometry. The two subunits have an RMS deviation of 0.29 A ngstrom for 248 C-alpha atoms and have average temperature factors of 18.9 and 15.9 Angstrom(2), respectively. In both subunits, the active site Lys 10 adopts an unusual phi, psi, combination. A comparison betw een the six known thermophilic and mesophilic TIM structures was condu cted in order to understand the higher stability of B. stearothermophi lus TIM. Although the ratio Arg/(ArgS+Lys) is higher in B. stearotherm ophilus TIM, the structure comparisons do not directly correlate this higher ratio to the better stability of the B. stearothermophilus enzy me. A higher number of prolines contributes to the higher stability of B. stearothermophilus TIM. Analysis of the known TIM sequences points out that the replacement of a structurally crucial asparagine by a hi stidine at the interface of monomers, thus avoiding the risk of deamid ation and thereby introducing a negative charge at the interface, may be one of the factors for adaptability at higher temperatures in the T IM family. Analysis of buried cavities and the areas lining these cavi ties also contributes to the greater thermal stability of the B. stear othermophilus enzyme. However, the most outstanding result of the stru cture comparisons appears to point to the hydrophobic stabilization of dimer formation by burying the largest amount of hydrophobic surface area in B. stearothermophilus TIM compared to all five other known TIM structures.