Department of Protein Biochemistry and Proteomics, Centre of the Region Haná for Biotechnological and Agricultural Research, Faculty of Science, Palacký University, Šlechtitelů 27, CZ-783 71 Olomouc, Czech Republic.
Institute for Integrative Biology of the Cell (I2BC), CNRS-CEA-Univ. Paris-Sud, Université Paris-Saclay, Avenue de la Terrasse, F-91198, Gif-sur-Yvette, France.
Biosci Rep. 2019 Apr 26;39(4). doi: 10.1042/BSR20190558. Print 2019 Apr 30.
Aldehyde dehydrogenases (ALDHs) constitute a superfamily of NAD(P)-dependent enzymes, which detoxify aldehydes produced in various metabolic pathways to the corresponding carboxylic acids. Among the 19 human ALDHs, the cytosolic ALDH9A1 has so far never been fully enzymatically characterized and its structure is still unknown. Here, we report complete molecular and kinetic properties of human ALDH9A1 as well as three crystal forms at 2.3, 2.9, and 2.5 Å resolution. We show that ALDH9A1 exhibits wide substrate specificity to aminoaldehydes, aliphatic and aromatic aldehydes with a clear preference for -trimethylaminobutyraldehyde (TMABAL). The structure of ALDH9A1 reveals that the enzyme assembles as a tetramer. Each ALDH monomer displays a typical ALDHs fold composed of an oligomerization domain, a coenzyme domain, a catalytic domain, and an inter-domain linker highly conserved in amino-acid sequence and folding. Nonetheless, structural comparison reveals a position and a fold of the inter-domain linker of ALDH9A1 never observed in any other ALDH so far. This unique difference is not compatible with the presence of a bound substrate and a large conformational rearrangement of the linker up to 30 Å has to occur to allow the access of the substrate channel. Moreover, the αβE region consisting of an α-helix and a β-strand of the coenzyme domain at the dimer interface are disordered, likely due to the loss of interactions with the inter-domain linker, which leads to incomplete β-nicotinamide adenine dinucleotide (NAD) binding pocket.
醛脱氢酶（ALDHs）构成了一个 NAD(P)依赖酶的超家族，其将各种代谢途径中产生的醛转化为相应的羧酸。在 19 个人类 ALDHs 中，细胞溶质 ALDH9A1 迄今尚未完全酶促表征，其结构仍然未知。在这里，我们报道了人 ALDH9A1 的完整分子和动力学特性以及三种晶体形式，分辨率分别为 2.3、2.9 和 2.5 Å。我们表明，ALDH9A1 对氨基酸醛、脂肪族和芳香族醛具有广泛的底物特异性，对 -三甲基氨基丁醛（TMABAL）具有明显的偏好。ALDH9A1 的结构表明，该酶组装为四聚体。每个 ALDH 单体显示出典型的 ALDHs 折叠，由一个寡聚结构域、一个辅酶结构域、一个催化结构域和一个高度保守的氨基酸序列和折叠的结构域间连接组成。尽管如此，结构比较显示 ALDH9A1 的结构域间连接的位置和折叠从未在任何其他 ALDH 中观察到。这种独特的差异与结合底物的存在不兼容，并且必须发生长达 30 Å 的连接子的大构象重排，以允许底物通道的进入。此外，由辅酶结构域二聚体界面上的一个α-螺旋和一个β-链组成的αβE 区域无序，可能是由于与结构域间连接子的相互作用丧失，导致β-烟酰胺腺嘌呤二核苷酸（NAD）结合口袋不完全。
