C-末端残基Arg缺失的D-海因酶的分子形式与稳定性

Molecular form and stability of D-hydantoinase deleted at C-terminal residue Arg

报道D-海因酶分子C-末端Arg残基的缺失,导致酶的解聚与稳定性的显著改变。用基因克隆、表达与纯化的方法,制备了重组D-海因酶(P479)及其C-末端残基Arg缺失的D-海因酶(P478)。SDS-PAGE和Native-PAGE分析表明,在完全相同的条件下,两者单体的分子量相同;但天然P479为二聚体,而P478为单体并保持约40%催化底物海因的活性。突变酶P478的pH值稳定性显著增加,抗SDS能力亦有所提高,但热稳定性明显降低。结果预示:D-海因酶的C-末端残基Arg显著影响酶的分子形式及热稳定性,虽也影响酶活性,但非酶活性所必需。

This report is about only deleting one C-terminal residue of D-hydantoinase to result in obvious changes on its molecular form and stability. A recombinant D-hydantoinase （P479） and its mutant enzyme deleted at C-terminal residue Arg （P478） were prepared by methods of gene cloning, expression and purification. Results show that the subunit molecular weight of P479 and P478 is the same （54kDa） as determined by SDS-PAGE, whilst the molecular form of native P479 and P478 is a dimer and a monomer respectively in the completely operative conditions. Compared with P479, the enzymatic activity of P478 for substrate hydantoin maintained about 40% and pH stability was obviously increased, at the alkaline side in particular, as well as the anti-SDS ability was also raised. However, the thermal stability for P478 was clearly lowed as compared to P479. It implies from above data that the C-terminal residue Arg of the D-hydantoinase is a crucial one for subunit dissociation, but non-essential for catalysis.