Department of Chemistry, University of Missouri-Columbia, Columbia, MO 65211, USA.
Arch Biochem Biophys. 2013 Oct 1;538(1):34-40. doi: 10.1016/j.abb.2013.07.024. Epub 2013 Aug 6.
The enzyme Δ(1)-pyrroline-5-carboxylate (P5C) dehydrogenase (aka P5CDH and ALDH4A1) is an aldehyde dehydrogenase that catalyzes the oxidation of γ-glutamate semialdehyde to l-glutamate. The crystal structures of mouse P5CDH complexed with glutarate, succinate, malonate, glyoxylate, and acetate are reported. The structures are used to build a structure-activity relationship that describes the semialdehyde carbon chain length and the position of the aldehyde group in relation to the cysteine nucleophile and oxyanion hole. Efficient 4- and 5-carbon substrates share the common feature of being long enough to span the distance between the anchor loop at the bottom of the active site and the oxyanion hole at the top of the active site. The inactive 2- and 3-carbon semialdehydes bind the anchor loop but are too short to reach the oxyanion hole. Inhibition of P5CDH by glyoxylate, malonate, succinate, glutarate, and l-glutamate is also examined. The Ki values are 0.27 mM for glyoxylate, 58 mM for succinate, 30 mM for glutarate, and 12 mM for l-glutamate. Curiously, malonate is not an inhibitor. The trends in Ki likely reflect a trade-off between the penalty for desolvating the carboxylates of the free inhibitor and the number of compensating hydrogen bonds formed in the enzyme-inhibitor complex.
Δ(1)-吡咯啉-5-羧酸 (P5C) 脱氢酶（又名 P5CDH 和 ALDH4A1）是一种醛脱氢酶，可催化 γ-谷氨酸半醛氧化为 l-谷氨酸。报告了与戊二酸盐、琥珀酸盐、丙二酸盐、乙醛酸和乙酸复合的鼠 P5CDH 的晶体结构。这些结构用于构建结构-活性关系，描述半醛碳链长度和醛基在半胱氨酸亲核试剂和氧阴离子孔的位置关系。有效的 4-和 5-碳底物具有共同的特征，即足够长以跨越活性位点底部的锚环和活性位点顶部的氧阴离子孔之间的距离。无活性的 2-和 3-碳半醛结合锚环，但太短而无法到达氧阴离子孔。还检查了 P5CDH 被乙醛酸、丙二酸盐、琥珀酸盐、戊二酸盐和 l-谷氨酸的抑制情况。Ki 值分别为 0.27 mM 对乙醛酸、58 mM 对琥珀酸盐、30 mM 对戊二酸盐和 12 mM 对 l-谷氨酸。奇怪的是，丙二酸盐不是抑制剂。Ki 值的趋势可能反映了在游离抑制剂的羧酸盐去溶剂化的惩罚和在酶-抑制剂复合物中形成的补偿氢键的数量之间的权衡。
