Conformational Changes Induced by P32T Substitution in Human Phosphatase ITPA

Enzyme ITPA participates in purine metabolism and its deficiency plays a role in several human diseases. There is growing evidence that ITPA polymorphism is also an important pharmacogen-ic phenotype, leading to a change in sensitivity to several drugs. ITPA deficiency exists in humans and is observed as elevated levels of ITP. Allele P32T-ITPA has more pronounced effects but the mecha-nism of enzyme inactivation is not known. Based on crystallographic data, Simone et al. assumed that the mutant loop containing P32T substitution led to uncovering of a hydrophobic residue (Phe31) that served as a marker for enzyme degradation. As the crystal structure of the enzyme may differ from the native structure in a solution, we tested this hypothesis using computer modeling. We simulated the structures of the wild-type homodimer and mutant homo- and heterodimers of the ITPA protein and analyzed these models at small time steps for detecting short-term effects of the conformations of the ITPA enzyme. Comparison of mutant structures with the wild-type structure revealed that the differences were more pronounced for the mutant homodimer than for the heterodimer. There were two regions of strong dis-tinctions – loops between α1-β2 and β5-β6. Two neighboring hydrophobic amino acids (Phe31 and Pro32) were changed by hydrophilic amino acids (Thr32 and Cys33) in the first loop (res. 28-33) due to mutation Phe31-Рro32Тhr-Cys33. The model structure differs from the crystal structure of P...
Source: Current Chemical Biology - Category: Biochemistry Source Type: research