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
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
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.