Conversion of Inactive Cobalamins to Coenzyme B12

描述（由申请人提供）：辅酶b12依赖过程对人类健康至关重要，在生态位和工业应用中发挥重要作用。拟议研究的长期目标是提高我们对辅酶b12的遗传学和生物化学的一般理解。提出的研究重点是无活性钴胺素代谢成b12辅酶。这个过程是外源钴胺素同化所必需的，因为b12辅酶是不稳定的，为了维持足够的b12库以满足生理需要。对参与钴胺素代谢的人cob(I)钴胺素腺苷转移酶进行生物化学表征，并确定其三维结构。将cob(II) alamin还原为cob(I)alamin用于辅酶b12的合成也将进行研究。初步研究表明，人蛋氨酸合酶还原酶可以将cob(II)alamin还原为cob(I)alamin，用于辅酶b12的合成，结果表明人蛋氨酸合酶还原酶与腺苷转移酶之间存在高度特异性的相互作用。人蛋氨酸合成酶还原酶将cob(II)alamin还原为cob(I)alamin的过程将得到更充分的表征。生物信息学分析结果表明，细菌YgfD蛋白及其同源物参与了钴胺素代谢，YgfD蛋白的具体功能将通过一系列生化试验来确定。该项目的最终目标将是利用本研究中鉴定的基因构建基因治疗载体，用于表达参与钴胺素代谢的酶。提出的研究将提供直接适用于改进b12代谢遗传性疾病的诊断和治疗方法的信息。此外，由于b12代谢的变化与慢性肝病、癌症、血清同型半胱氨酸升高（可能是心脏病的危险因素）、DNA损伤率增加、认知功能受损和艾滋病毒感染有关，因此拟议的研究也可能为了解这些疾病提供相关信息。

DESCRIPTION (provided by applicant): Coenzyme B12-dependent processes are vital to human health and play important roles in ecological niches and industrial applications. The long-term goal of the proposed research is to improve our general understanding of the genetics and biochemistry of coenzyme B 12. The proposed studies focus on the metabolism of inactive cobalamins into the B 12 coenzymes. This process is needed for the assimilation of exogenous cobalamins, and because the B 12 coenzymes are unstable, for the maintenance of adequate B 12 pools to meet physiological needs. The human cob(I)alamin adenosyltransferase which functions in cobalamin metabolism will be characterized biochemically and its 3-dimensional structure will be determined. The reduction of cob(II) alamin to cob(I)alamin for coenzyme B 12 synthesis will also be investigated. Preliminary studies showed that the human methionine synthase reductase can reduce cob(II)alamin to cob(I)alamin for coenzyme B 12 synthesis, and results indicated a highly specific interaction between the human methionine synthase reductase and adenosyltransferase enzymes. The reduction of cob(II)alamin to cob(I)alamin by the human methionine synthase reductase will be more fully characterized. The results of bioinformatic analyses have indicated that the bacterial YgfD protein and its homologues are involved in cobalamin metabolism The specific function of the YgfD protein will be determined by a series of biochemical tests. The final aim of the project will be to use the genes identified in this study to construct gene therapy vectors for expression of enzymes involved in cobalamin metabolism. The proposed studies will provide information directly applicable to improved methods of diagnosis and treatment of inherited diseases of B 12 metabolism. Furthermore, since changes in B 12 metabolism have been linked to chronic liver disease, cancer, elevated serum homocysteine (a possible risk factor in heart disease), increased rates of DNA damage, impaired cognitive function, and HIV infection, the proposed studies may also provide information relevant to understanding these diseases.