1242619-20-0Relevant articles and documents
Structural mutations that probe the interactions between the catalytic and dianion activation sites of triosephosphate isomerase
Zhai, Xiang,Amyes, Tina L.,Wierenga, Rik K.,Loria, J. Patrick,Richard, John P.
, p. 5928 - 5940 (2013)
Triosephosphate isomerase (TIM) catalyzes the isomerization of dihydroxyacetone phosphate to form d-glyceraldehyde 3-phosphate. The effects of two structural mutations in TIM on the kinetic parameters for catalysis of the reaction of the truncated substrate glycolaldehyde (GA) and the activation of this reaction by phosphite dianion are reported. The P168A mutation results in similar 50- and 80-fold decreases in (kcat/Km)E and (kcat/Km)E·HPi, respectively, for deprotonation of GA catalyzed by free TIM and by the TIM·HPO 32- complex. The mutation has little effect on the observed and intrinsic phosphite dianion binding energy or the magnitude of phosphite dianion activation of TIM for catalysis of deprotonation of GA. A loop 7 replacement mutant (L7RM) of TIM from chicken muscle was prepared by substitution of the archaeal sequence 208-TGAG with 208-YGGS. L7RM exhibits a 25-fold decrease in (kcat/Km)E and a larger 170-fold decrease in (kcat/Km)E·HPi for reactions of GA. The mutation has little effect on the observed and intrinsic phosphodianion binding energy and only a modest effect on phosphite dianion activation of TIM. The observation that both the P168A and loop 7 replacement mutations affect mainly the kinetic parameters for TIM-catalyzed deprotonation but result in much smaller changes in the parameters for enzyme activation by phosphite dianion provides support for the conclusion that catalysis of proton transfer and dianion activation of TIM take place at separate, weakly interacting, sites in the protein catalyst.
Role of Loop-Clamping Side Chains in Catalysis by Triosephosphate Isomerase
Zhai, Xiang,Amyes, Tina L.,Richard, John P.
supporting information, p. 15185 - 15197 (2015/12/18)
The side chains of Y208 and S211 from loop 7 of triosephosphate isomerase (TIM) form hydrogen bonds to backbone amides and carbonyls from loop 6 to stabilize the caged enzyme-substrate complex. The effect of seven mutations [Y208T, Y208S, Y208A, Y208F, S211G, S211A, Y208T/S211G] on the kinetic parameters for TIM catalyzed reactions of the whole substrates dihydroxyacetone phosphate and d-glyceraldehyde 3-phosphate [(kcat/Km)GAP and (kcat/Km)DHAP] and of the substrate pieces glycolaldehyde and phosphite dianion (kcat/KHPiKGA) are reported. The linear logarithmic correlation between these kinetic parameters, with slope of 1.04 ± 0.03, shows that most mutations of TIM result in an identical change in the activation barriers for the catalyzed reactions of whole substrate and substrate pieces, so that the transition states for these reactions are stabilized by similar interactions with the protein catalyst. The second linear logarithmic correlation [slope = 0.53 ± 0.16] between kcat for isomerization of GAP and Kd? for phosphite dianion binding to the transition state for wildtype and many mutant TIM-catalyzed reactions of substrate pieces shows that ca. 50% of the wildtype TIM dianion binding energy, eliminated by these mutations, is expressed at the wildtype Michaelis complex, and ca. 50% is only expressed at the wildtype transition state. Negative deviations from this correlation are observed when the mutation results in a decrease in enzyme reactivity at the catalytic site. The main effect of Y208T, Y208S, and Y208A mutations is to cause a reduction in the total intrinsic dianion binding energy, but the effect of Y208F extends to the catalytic site.
Role of Lys-12 in catalysis by triosephosphate isomerase: A two-part substrate approach
Go, Maybelle K.,Koudelka, Astrid,Amyes, Tina L.,Richard, John P.
experimental part, p. 5377 - 5389 (2011/03/22)
We report that the K12G mutation in triosephosphate isomerase (TIM) from Saccharomyces cerevisiae results in (1) a ～50-fold increase in Km for the substrate glyceraldehyde 3-phosphate (GAP) and a 60-fold increase in Ki for competitive inhibition by the intermediate analogue 2-phosphoglycolate, resulting from the loss of stabilizing ground state interactions between the alkylammonium side chain of Lys-12 and the ligand phosphodianion group; (2) a 12000-fold decrease in kcat for isomerization of GAP, suggesting a tightening of interactions between the side chain of Lys-12 and the substrate on proceeding from the Michaelis complex to the transition state; and (3) a 6 - 105-fold decrease in k cat/Km, corresponding to a total 7.8 kcal/mol stabilization of the transition state by the cationic side chain of Lys-12. The yields of the four products of the K12G TIM-catalyzed isomerization of GAP in D2O were quantified as dihydroxyacetone phosphate (DHAP) (27%), [1(R)-2H]DHAP (23%), [2(R)-2H]GAP (31%), and methylglyoxal (18%) from an enzyme-ca alyzed elimination reaction. The K12G mutation has only a small effect on the relative yields of the three products of the transfer of a proton to the TIM-bound enediol(ate) intermediate in D2O, but it strongly favors catalysis of the elimination reaction to give methylglyoxal. The K12G mutation also results in a ≥14-fold decrease in kcat/K m for isomerization of bound glycolaldehyde (GA), although the dominant observed product of the mutant enzyme-catalyzed reaction of [1- 13C]GA in D2O is [1-13C,2,2-di-2H]GA from a nonspecific protein-catalyzed reaction. The observation that the K12G mutation results in a large decrease in kcat/Km for the reactions of both GAP and the neutral truncated substrate [1-13C]GA provides evidence for a stabilizing interaction between the cationic side chain of Lys-12 and the negative charge that develops at the enolate-like oxygen in the transition state for deprotonation of the sugar substrate ";piece";.
