Deflavination Of Bacillus Sp. Sarcosine Oxidase And Reconstitution Of Enzyme With Cofactors

The flavoprotein sarcosine oxidase(Sarcosine oxidase, EC 1.5.3.1, SOX), with flavin adenine dinucleotide(FAD), catalyzes N-methyl-redox on sarcosine, therefore can be used for assay of creatinine content in serum or urine. This study was to explore the interaction between sarcosine oxidase and cofactor /ligand to reveal the impact of flavin structure on flavin enzyme configuration and function. By refolding of the inclusion bodies of recombinant sarcosine oxidase apo-protein(apo-SOX), the assembly of apo-SOX and cofactor analogue were performed. The main results include:(1) A rapid and efficient method of SOX cofactor reject/reconstruction system was established. The apo-SOX inclusion bodies were dialysis-refolded. Specific methods of adding cofactors during apo-SOX refolding process were explored, which were expected to help assembly of apo-SOX and the cofactors, and to retain the enzymatic activity. The optimal conditions of apo-SOX refolding were shown as follow: enzyme protein concentration of 0.3 mg·m L-1, outer dialysate pH of 8.5, temperature of 4 °C, the redox value(GSH/GSSG) of 2.0, and renaturation time of 24 h.(2) Based on the core structure of FAD/FMN isoalloxazine ring, cofactor ligand was rationally designed, optimized and screened. The modification of core structure of flavin isoalloxazine ring was simulated, and some featured cofactor analogue were selected. Bacillus sp. NS-129(PDB code: 1zov) was used as the template for SOX 3D structure homology modeling. The cofactor and enzyme docking process was simulated using Accelrys Discovery Studio and www.Swiss-Dock.com online software. In addition, natural cofactor FMN, riboflavin and artificial cofactors were also selected for comparing the interaction between apoprotein and cofactors. Parameters in simulation including number of hydrogen bonds, energy and Fullfitness were carefully detected and abalysized. The simulation results provides theoretical reference for further study.(3) It was shown that reconstruction of apo-SOX and their cofactors cause remarkable changes on the secondary structure, enzymatic activity and stability of the SOX in complex with cofactors. The site 3-N of the triazine ring in ligand structure was essential to the holoenzyme of SOX, which affecting the assembly of apo-protein and triazine ring. It also plays a key role in the in the electron oxidation transfer chain. Changing of 3-N site caused the enzymatic activity lowering down to only 20% of the natural SOX. Unlike the site 3-N, the alternation of site 7-C and 8-C had less affection on the enzyme structure. The flavin enzymes might have different mechanisms on constitution of holoenzme from apoprotein and cofactors, there might be varies modification methods suitable for other individual flavor-enzymes.