Department of Biology, University of Konstanz, Universitätsstrasse 10, 78457 Konstanz, Germany.
Department of Chemistry, University of Konstanz, Universitätsstrasse 10, 78457 Konstanz, Germany.
Acta Crystallogr F Struct Biol Commun. 2023 Aug 1;79(Pt 8):217-223. doi: 10.1107/S2053230X2300571X. Epub 2023 Aug 9.
Members of the GCN5-related N-acetyltransferase (GNAT) family are found in all domains of life and are involved in processes ranging from protein synthesis and gene expression to detoxification and virulence. Due to the variety of their macromolecular targets, GNATs are a highly diverse family of proteins. Currently, 3D structures of only a small number of GNAT representatives are available and thus the family remains poorly characterized. Here, the crystal structure of the guanidine riboswitch-associated GNAT from Lactobacillus curiae (LcGNAT) that acetylates canavanine, a structural analogue of arginine with antimetabolite properties, is reported. LcGNAT shares the conserved fold of the members of the GNAT superfamily, but does not contain an N-terminal β0 strand and instead contains a C-terminal β7 strand. Its P-loop, which coordinates the pyrophosphate moiety of the acetyl-coenzyme A cosubstrate, is degenerated. These features are shared with its closest homologues in the polyamine acetyltransferase subclass. Site-directed mutagenesis revealed a central role of the conserved residue Tyr142 in catalysis, as well as the semi-conserved Tyr97 and Glu92, suggesting that despite its individual substrate specificity LcGNAT performs the classical reaction mechanism of this family.
GCN5 相关的 N-乙酰转移酶 (GNAT) 家族成员存在于所有生命领域，参与从蛋白质合成和基因表达到解毒和毒力等各种过程。由于其大分子靶标的多样性，GNAT 是一个高度多样化的蛋白质家族。目前，只有少数 GNAT 代表的 3D 结构可用，因此该家族的特征仍然很差。在这里，报道了来自乳杆菌（LcGNAT）的胍基核苷开关相关 GNAT 的晶体结构，该酶可以乙酰化瓜氨酸，瓜氨酸是具有抗代谢特性的精氨酸结构类似物。LcGNAT 具有 GNAT 超家族成员的保守折叠，但不包含 N 端β0 链，而是包含 C 端β7 链。其 P 环与乙酰辅酶 A 共底物的焦磷酸部分配位，退化。这些特征与其在聚胺乙酰转移酶亚类中最接近的同源物共享。定点突变揭示了保守残基 Tyr142 在催化中的核心作用，以及半保守的 Tyr97 和 Glu92，表明尽管其具有单个底物特异性，LcGNAT 仍执行该家族的经典反应机制。
