Glu571 of PheT plays a pivotal role in the thermal stability of Escherichia coli PheRS enzyme
2018
Ashwin Sri Bala, Sridar | Madhumathi, Irulappan | Vinodha, Sengottuvel | Munavar, M Hussain
As of date the two temperature sensitive mutations isolated in pheST operon include pheS5 (G₂₉₃→A₂₉₃) and pheT354. Recently, we reported that G₆₇₃ of pheS defines a hot spot for intragenic suppressors of pheS5. In this investigation, in 13 independent experiments, a collection of temperature sensitive mutants were isolated by localized mutagenesis. Complementation using clones bearing pheS⁺, pheT⁺, and pheS⁺T⁺ indicated that 34 mutants could harbor lesion(s) in pheS and four could be in pheT and one mutant might be a double mutant. Surprisingly, all the 34 pheS mutants harbored the very same (G₂₉₃→A₂₉₃) transition mutation as present in the classical pheS5 mutant. Most unexpectedly, the four pheT mutants isolated harbored the same G₁₇₁₁→A₁₇₁₁ transition, a mutation which is hitherto unreported. Since all the four pheT mutants were defined by the same G₁₇₁₁→A₁₇₁₁ base change, we believe that getting other mutations could be hard hitting and therefore it is proposed that G₁₇₁₁ itself could be a “hot spot” for emergence of Ts mutations in pheT and similarly G₂₉₃ itself could be a “hot spot” for Ts lesions in pheS. These results clearly imply a vital role for Glutamic acid₅₇₁ (Glu₅₇₁) of PheT and reinforce criticality of Glycine₉₈ (Gly₉₈) of PheS in the thermal stability of PheRS enzyme.
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