Guo Junhong, Huang Fanglu, Huang Chuan, Duan Xiaobo, Jian Xinyun, Leeper Finian, Deng Zixin, Leadlay Peter F, Sun Yuhui
Key Laboratory of Combinatorial Biosynthesis and Drug Discovery (Ministry of Education), and School of Pharmaceutical Sciences, Wuhan University, Wuhan, Wuchang 430071, People's Republic of China.
Department of Biochemistry, University of Cambridge, Cambridge CB2 1GA, UK.
Chem Biol. 2014 May 22;21(5):608-18. doi: 10.1016/j.chembiol.2014.03.005. Epub 2014 Apr 17.
Gentamicin C complex is a mixture of aminoglycoside antibiotics used to treat severe Gram-negative bacterial infections. We report here key features of the late-stage biosynthesis of gentamicins. We show that the intermediate gentamicin X2, a known substrate for C-methylation at C-6' to form G418 catalyzed by the radical SAM-dependent enzyme GenK, may instead undergo oxidation at C-6' to form an aldehyde, catalyzed by the flavin-linked dehydrogenase GenQ. Surprisingly, GenQ acts in both branches of the pathway, likewise oxidizing G418 to an analogous ketone. Amination of these intermediates, catalyzed mainly by aminotransferase GenB1, produces the known intermediates JI-20A and JI-20B, respectively. Other pyridoxal phosphate-dependent enzymes (GenB3 and GenB4) act in enigmatic dehydroxylation steps that convert JI-20A and JI-20B into the gentamicin C complex or (GenB2) catalyze the epimerization of gentamicin C2a into gentamicin C2.
庆大霉素C复合物是一种用于治疗严重革兰氏阴性细菌感染的氨基糖苷类抗生素混合物。我们在此报告庆大霉素后期生物合成的关键特征。我们发现，中间体庆大霉素X2是一种已知的在C-6'处进行C-甲基化以形成G418的底物，由依赖于自由基SAM的酶GenK催化，相反，它可能在C-6'处发生氧化形成醛，由黄素连接的脱氢酶GenQ催化。令人惊讶的是，GenQ在该途径的两个分支中均起作用，同样将G418氧化为类似的酮。这些中间体的胺化反应主要由转氨酶GenB1催化，分别产生已知的中间体JI-20A和JI-20B。其他依赖磷酸吡哆醛的酶（GenB3和GenB4）在神秘的脱羟基步骤中起作用，将JI-20A和JI-20B转化为庆大霉素C复合物，或者（GenB2）催化庆大霉素C2a差向异构化为庆大霉素C2。
