Kanosamine is an antibiotic and antifungal monosaccharide. The kanosamine biosynthetic pathway from glucose 6-phosphate in Bacillus cereus UW85 was recently reported, and the functions of each of the three enzymes in the pathway, KabA, KabB and KabC, were demonstrated. KabA, a member of a subclass of the VI_β family of PLP-dependent aminotransferases, catalyzes the second step in the pathway, generating kanosamine 6-phosphate (K6P) using l-glutamate as the amino-donor. KabA catalysis was shown to be extremely efficient, with a second-order rate constant with respect to K6P transamination of over 10⁷ M⁻¹s⁻¹. Here we report the high-resolution structure of KabA in both the PLP- and PMP-bound forms. In addition, co-crystallization with K6P allowed the structure of KabA in complex with the covalent PLP-K6P adduct to be solved. Co-crystallization or soaking with glutamate or 2-oxoglutarate did not result in crystals with either substrate/product. Reduction of the PLP-KabA complex with sodium cyanoborohydride gave an inactivated enzyme, and crystals of the reduced KabA were soaked with the l-glutamate analog glutarate to mimic the KabA-PLP-l-glutamate complex. Together these four structures give a complete picture of how the active site of KabA recognizes substrates for each half-reaction. The KabA structure is discussed in the context of homologous aminotransferases.

Kanosamine 是一种抗生素和抗真菌单糖。最近报道了蜡状芽孢杆菌UW85 中葡萄糖 6-磷酸的卡诺胺生物合成途径，并证明了该途径中的三种酶 KabA、KabB 和 KabC 中的每一种的功能。KabA是 PLP 依赖性转氨酶 VI _β家族的一个亚类成员，它催化该途径的第二步，使用L-谷氨酸作为氨基供体生成 6-磷酸卡诺胺 (K6P) 。KabA 催化被证明是非常有效的，对于 K6P 转氨反应的二级速率常数超过 10 ⁷ M ^-1 s ^-1. 在这里，我们报告了 PLP 和 PMP 绑定形式的 KabA 的高分辨率结构。此外，与 K6P 的共结晶使得 KabA 与共价 PLP-K6P 加合物复合的结构得以解决。与谷氨酸或 2-酮戊二酸共结晶或浸泡不会导致与底物/产物的任何一种晶体。用氰基硼氢化钠还原 PLP-KabA 复合物得到灭活的酶，用 L-谷氨酸类似物戊二酸盐浸泡还原的 KabA 晶体以模拟 KabA-PLP- 1-谷氨酸复合物。这四种结构共同给出了 KabA 的活性位点如何识别每个半反应的底物的完整画面。KabA 结构在同源转氨酶的背景下讨论。