Conformational changes to 1,4-β-D-glucan cellobiohydrolase I (CBHI) in response to its binding with p-nitrophenyl β-D-cellobioside (PNPC) were analyzed by second-derivative fluorescence spectrometry at the saturatio...Conformational changes to 1,4-β-D-glucan cellobiohydrolase I (CBHI) in response to its binding with p-nitrophenyl β-D-cellobioside (PNPC) were analyzed by second-derivative fluorescence spectrometry at the saturation binding point. Irreversible changes to the configuration of PNPC during the course of the binding process were characterized by UV spectral analysis. Isothermal titration calorimetry (ITC) was used to determine the stoichiometry of binding (i.e. the number of molar binding sites) of PNPC to CBHI. Two points on the surface of the CBHI molecule interact with PNPC, and irreversible changes to the configuration of PNPC occur during its conversion to p-nitrophenyl (PNP). The ITC studies demonstrated that the binding of PNPC to CBHI is an irreversible process, in which heat is released, but where there is no reversible equilibrium between PNPC-CBHI and CBHI and PNPC. On the other hand, PNP and cellobiose need to be released from the PNPC-CBHI complex to facilitate the repeated binding of new PNPC molecules to the renewable CBHI molecules. Therefore, we speculate that the energy, which powers the configurational change of PNPC as it is converted to PNP, is generated from cyclic changes in the conformation of CBHI during the binding/de-sorption process. These new insights may provide a basis for a better understanding of the binding mechanism in enzyme-substrate interactions.展开更多
黑曲霉Aspergillus niger发酵豆渣产β-葡萄糖苷酶(BGL)。粗酶液依次经过乙醇沉淀和DEAE-Sepharose Fast Flow离子交换层析,获得了两种电泳纯的β-葡萄糖苷酶BGL1和BGL2,它们的相对分子质量分别为102kDa、97kDa,总酶活回收率达到48%。在...黑曲霉Aspergillus niger发酵豆渣产β-葡萄糖苷酶(BGL)。粗酶液依次经过乙醇沉淀和DEAE-Sepharose Fast Flow离子交换层析,获得了两种电泳纯的β-葡萄糖苷酶BGL1和BGL2,它们的相对分子质量分别为102kDa、97kDa,总酶活回收率达到48%。在pH2.5及温度为55℃时,两种BGL水解京尼平苷的速度均达到最大;BGL水解活性受到Na+的激活但不受K+的影响,但Mg2+、Ba2+、Cu2+、Fe2+、Zn2+和Hg+等离子对BGL活性有不同程度的抑制作用(其中对BGL1的抑制普遍强于BGL2),而且同一种离子对不同BGL活性的影响性质不同,Ca2+显著激活BGL1而对BGL2无影响,Fe3+显著抑制BGL1而激活BGL2。在同样条件下,BGL对对硝基苯-β-D吡喃葡萄糖苷(pNPGlu)、对硝基苯-β-D吡喃半乳糖苷(pNPGal)和水杨苷均有催化活性,其中对pNPGlu的Km值最小,BGL1、BGL2分别为0.764和1.934mmol/L;而BGL对京尼平苷水解的催化效率最高,BGL1、BGL2的Kcat/Km值分别为4.28×104和1.04×105L/mol·s。BGL1、BGL2活性的pH稳定范围相近,分别为pH2.0-7.0、pH2.0-8.5,但它们的热稳定性差异较大,55℃时BGL2保温60min,酶活保留了60%,而BGL1的酶活半衰期只有10min。展开更多
基金the National Natural Science Foundation of China (Grant Nos. 30370013 and 30500007)
文摘Conformational changes to 1,4-β-D-glucan cellobiohydrolase I (CBHI) in response to its binding with p-nitrophenyl β-D-cellobioside (PNPC) were analyzed by second-derivative fluorescence spectrometry at the saturation binding point. Irreversible changes to the configuration of PNPC during the course of the binding process were characterized by UV spectral analysis. Isothermal titration calorimetry (ITC) was used to determine the stoichiometry of binding (i.e. the number of molar binding sites) of PNPC to CBHI. Two points on the surface of the CBHI molecule interact with PNPC, and irreversible changes to the configuration of PNPC occur during its conversion to p-nitrophenyl (PNP). The ITC studies demonstrated that the binding of PNPC to CBHI is an irreversible process, in which heat is released, but where there is no reversible equilibrium between PNPC-CBHI and CBHI and PNPC. On the other hand, PNP and cellobiose need to be released from the PNPC-CBHI complex to facilitate the repeated binding of new PNPC molecules to the renewable CBHI molecules. Therefore, we speculate that the energy, which powers the configurational change of PNPC as it is converted to PNP, is generated from cyclic changes in the conformation of CBHI during the binding/de-sorption process. These new insights may provide a basis for a better understanding of the binding mechanism in enzyme-substrate interactions.
文摘黑曲霉Aspergillus niger发酵豆渣产β-葡萄糖苷酶(BGL)。粗酶液依次经过乙醇沉淀和DEAE-Sepharose Fast Flow离子交换层析,获得了两种电泳纯的β-葡萄糖苷酶BGL1和BGL2,它们的相对分子质量分别为102kDa、97kDa,总酶活回收率达到48%。在pH2.5及温度为55℃时,两种BGL水解京尼平苷的速度均达到最大;BGL水解活性受到Na+的激活但不受K+的影响,但Mg2+、Ba2+、Cu2+、Fe2+、Zn2+和Hg+等离子对BGL活性有不同程度的抑制作用(其中对BGL1的抑制普遍强于BGL2),而且同一种离子对不同BGL活性的影响性质不同,Ca2+显著激活BGL1而对BGL2无影响,Fe3+显著抑制BGL1而激活BGL2。在同样条件下,BGL对对硝基苯-β-D吡喃葡萄糖苷(pNPGlu)、对硝基苯-β-D吡喃半乳糖苷(pNPGal)和水杨苷均有催化活性,其中对pNPGlu的Km值最小,BGL1、BGL2分别为0.764和1.934mmol/L;而BGL对京尼平苷水解的催化效率最高,BGL1、BGL2的Kcat/Km值分别为4.28×104和1.04×105L/mol·s。BGL1、BGL2活性的pH稳定范围相近,分别为pH2.0-7.0、pH2.0-8.5,但它们的热稳定性差异较大,55℃时BGL2保温60min,酶活保留了60%,而BGL1的酶活半衰期只有10min。