Department of Chemistry, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5C9, Canada.
Department of Chemistry, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5C9, Canada.
J Biol Chem. 2013 Nov 22;288(47):34121-34130. doi: 10.1074/jbc.M113.500637. Epub 2013 Oct 4.
NtdA from Bacillus subtilis is a sugar aminotransferase that catalyzes the pyridoxal phosphate-dependent equatorial transamination of 3-oxo-α-D-glucose 6-phosphate to form α-D-kanosamine 6-phosphate. The crystal structure of NtdA shows that NtdA shares the common aspartate aminotransferase fold (Type 1) with residues from both monomers forming the active site. The crystal structures of NtdA alone, co-crystallized with the product α-D-kanosamine 6-phosphate, and incubated with the amine donor glutamate reveal three key structures in the mechanistic pathway of NtdA. The structure of NtdA alone reveals the internal aldimine form of NtdA with the cofactor pyridoxal phosphate covalently attached to Lys-247. The addition of glutamate results in formation of pyridoxamine phosphate. Co-crystallization with kanosamine 6-phosphate results in the formation of the external aldimine. Only α-D-kanosamine 6-phosphate is observed in the active site of NtdA, not the β-anomer. A comparison of the structure and sequence of NtdA with other sugar aminotransferases enables us to propose that the VIβ family of aminotransferases should be divided into subfamilies based on the catalytic lysine motif.
枯草芽孢杆菌 NtdA 是一种糖基氨基转移酶，可催化吡哆醛磷酸依赖的 3-氧-α-D-葡萄糖 6-磷酸的赤道氨基转移，形成 α-D-甘露糖胺 6-磷酸。NtdA 的晶体结构表明，NtdA 与来自两个单体的残基共享常见的天冬氨酸氨基转移酶折叠（类型 1），形成活性位点。NtdA 单独的晶体结构、与产物 α-D-甘露糖胺 6-磷酸共结晶的结构以及与胺供体谷氨酸孵育的结构揭示了 NtdA 机制途径中的三个关键结构。NtdA 单独的结构揭示了 NtdA 的内部亚胺形式，辅因子吡哆醛磷酸与 Lys-247 共价连接。谷氨酸的加入导致吡哆醛磷酸的形成。与甘露糖 6-磷酸共结晶导致外部亚胺的形成。在 NtdA 的活性位点仅观察到 α-D-甘露糖胺 6-磷酸，而不是β-异构体。将 NtdA 的结构和序列与其他糖基氨基转移酶进行比较，使我们能够提出 VIβ 家族的氨基转移酶应该根据催化赖氨酸基序分为亚家族。
