Moore S A, Baker H M, Blythe T J, Kitson K E, Kitson T M, Baker E N
Institute of Molecular Biosciences, Massey University, Private Bag, 11-222, Palmerston North, New Zealand.
Structure. 1998 Dec 15;6(12):1541-51. doi: 10.1016/s0969-2126(98)00152-x.
. Enzymes of the aldehyde dehydrogenase family are required for the clearance of potentially toxic aldehydes, and are essential for the production of key metabolic regulators. The cytosolic, or class 1, aldehyde dehydrogenase (ALDH1) of higher vertebrates has an enhanced specificity for all-trans retinal, oxidising it to the powerful differentiation factor all-trans retinoic acid. Thus, ALDH1 is very likely to have a key role in vertebrate development.
. The three-dimensional structure of sheep ALDH1 has been determined by X-ray crystallography to 2.35 A resolution. The overall tertiary and quaternary structures are very similar to those of bovine mitochondrial ALDH (ALDH2), but there are important differences in the entrance tunnel for the substrate. In the ALDH1 structure, the sidechain of the general base Glu268 is disordered and the NAD+ cofactor binds in two distinct modes.
. The submicromolar Km of ALDH1 for all-trans retinal, and its 600-fold enhanced affinity for retinal compared to acetaldehyde, are explained by the size and shape of the substrate entrance tunnel in ALDH1. All-trans retinal fits into the active-site pocket of ALDH1, but not into the pocket of ALDH2. Two helices and one surface loop that line the tunnel are likely to have a key role in defining substrate specificity in the wider ALDH family. The relative sizes of the tunnels also suggest why the bulky alcohol aversive drug disulfiram reacts more rapidly with ALDH1 than ALDH2. The disorder of Glu268 and the observation that NAD+ binds in two distinct modes indicate that flexibility is a key facet of the enzyme reaction mechanism.
醛脱氢酶家族的酶对于清除潜在有毒醛类是必需的，并且对于关键代谢调节物的产生至关重要。高等脊椎动物的胞质或1类醛脱氢酶（ALDH1）对全反式视黄醛具有增强的特异性，将其氧化为强大的分化因子全反式视黄酸。因此，ALDH1很可能在脊椎动物发育中起关键作用。
通过X射线晶体学已确定绵羊ALDH1的三维结构，分辨率为2.35埃。总体三级和四级结构与牛线粒体ALDH（ALDH2）的结构非常相似，但底物进入通道存在重要差异。在ALDH1结构中，通用碱基Glu268的侧链无序，NAD +辅因子以两种不同模式结合。
ALDH1对全反式视黄醛的亚微摩尔Km值及其与乙醛相比对视黄醛增强600倍的亲和力，可由ALDH1中底物进入通道的大小和形状来解释。全反式视黄醛适合进入ALDH1的活性位点口袋，但不适合进入ALDH2的口袋。构成通道的两个螺旋和一个表面环可能在定义更广泛的ALDH家族中的底物特异性方面起关键作用。通道的相对大小也说明了为什么体积庞大的酒精厌恶药物双硫仑与ALDH1的反应比与ALDH2的反应更快。Glu268的无序以及NAD +以两种不同模式结合的观察结果表明，灵活性是酶反应机制的一个关键方面。
