Tyr78-loop对鱼腥藻来源苯丙氨酸脱氨酶活性的影响

Influence of Tyr78-loop on phenylalanine ammonia-lyase from Anabaena variabilis

摘要:

【背景】MIO (Methylidene-imidazol-5-one)依赖型酶中，催化因子Tyr所在loop (Tyr78-loop)的灵活性显著影响酶学性质。【目的】探讨Tyr78-loop对鱼腥藻来源苯丙氨酸脱氨酶酶活的影响，以提高其反应活性。【方法】将该酶的Tyr78-loop进行分子改造，筛选出酶活提高的突变体，并对突变酶的酶学性质进行研究。【结果】突变体S73N、E95V、E95K和S73N/E95K在37 °C、pH 8.5下比活分别比原酶提高了34%、30%、18%和35%。蛋白三维结构模拟推测在突变体S73N、E95V和E95K中，位于α螺旋与Tyr78-loop交界处的Asn73、Val95和Lys95与附近氨基酸的氢键作用力数目减少，一定程度上增加了Tyr78-loop的柔性。【结论】Ser73位和Glu95位氨基酸的突变增加了Tyr78-loop的灵活性，提高了苯丙氨酸脱氨酶的酶活。

Abstract:

[Background] Enzymatic property of the MIO-dependent (methylidene-imidazol-5-one) enzyme is significantly affected by the flexibility of the special loop that includes the catalysis Tyr (Tyr78-loop). [Objective] The effect of Tyr78-loop on activity of phenylalanine ammonia-lyase (PAL) from Anabaena variabilis was investigated to improve PAL catalytic activity. [Methods] Tyr78-loop was genetically modified. Positive mutants with enhanced activity were selected, followed by characterization. [Results] The specific activities of S73N, E95V, E95K and S73N/E95K mutants were improved by 34%, 30%, 18% and 35%, respectively, compared with that of the wild type at 37 °C and pH 8.5. According to protein structure simulation, the amino acid sites Asn73, Val95 and Lys95 in the mutants S73N, E95V and E95K, which located at the junction of α-helix and Tyr78-loop, had fewer hydrogen bonds with the nearby amino acids. This would increase the flexibility of Tyr78-loop and result in enhancement of the enzyme activity. [Conclusion] Catalytic activity of AvPAL could be improved by increasing the flexibility of Tyr78-loop through mutation on the Ser73 and Glu95 sites.