The structure of lincomycin A consists of the unusual eight-carbon thiosugar core methyllincosamide (MTL) decorated with a pendent N-methylprolinyl moiety. Previous studies on MTL biosynthesis have suggested GDP-ᴅ-erythro-α-ᴅ-gluco-octose and GDP-ᴅ-α-ᴅ-lincosamide as key intermediates in the pathway. However, the enzyme-catalyzed reactions resulting in the conversion of GDP-ᴅ-erythro-α-ᴅ-gluco-octose to GDP-ᴅ-α-ᴅ-lincosamide have not yet been elucidated. Herein, a biosynthetic subpathway involving the activities of four enzymes—LmbM, LmbL, CcbZ, and CcbS (the LmbZ and LmbS equivalents in the closely related celesticetin pathway)—is reported. These enzymes catalyze the previously unknown biosynthetic steps including 6-epimerization, 6,8-dehydration, 4-epimerization, and 6-transamination that convert GDP-ᴅ-erythro-α-ᴅ-gluco-octose to GDP-ᴅ-α-ᴅ-lincosamide. Identification of these reactions completes the description of the entire lincomycin biosynthetic pathway. This work is significant since it not only resolves the missing link in octose core assembly of a thiosugar-containing natural product but also showcases the sophistication in catalytic logic of enzymes involved in carbohydrate transformations.

林可霉素A的结构由不寻常的八碳硫糖核心甲基林可酰胺（MTL）修饰，并带有侧垂的N-甲基脯氨酰基部分。以前关于MTL生物合成的研究表明，GDP-α-赤型-α-β-葡萄糖-八糖和GDP-β-α-α-林可酰胺是该途径的关键中间体。然而，酶催化的反应导致GDP-ᴅ-赤型-α-ᴅ-葡萄糖的转化β-辛基糖对GDP-α-α-α-林可酰胺尚未阐明。在本文中，报道了涉及四种酶（LmbM，LmbL，CcbZ和CcbS（在紧密相关的Celesticetin途径中的LmbZ和LmbS等效物））的活性的生物合成子途径。这些酶催化了以前未知的生物合成步骤，包括将GDP-ᴅ-赤型-α-ᴅ-葡萄糖转化为6-电子化，6,8-脱水，4-电子化和6-氨基化-辛酸至GDP-α-α-α-林可酰胺。这些反应的鉴定完成了整个林可霉素生物合成途径的描述。这项工作意义重大，因为它不仅解决了含硫糖天然产物的八糖核心组装中的缺失环节，而且展示了碳水化合物转化所涉及的酶催化逻辑的复杂性。