Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada.
Department of Chemistry, St. Francis Xavier University, Antigonish, Nova Scotia B2G 2W5, Canada.
Bioorg Med Chem Lett. 2014 Jan 1;24(1):390-3. doi: 10.1016/j.bmcl.2013.10.061. Epub 2013 Nov 4.
d-Amino acids can play important roles as specific biosynthetic building blocks required by organisms or act as regulatory molecules. Consequently, amino acid racemases that catalyze the formation of d-amino acids are potential therapeutic targets. Serine racemase catalyzes the reversible formation of d-serine (a modulator of neurotransmission) from l-serine, while proline racemase (an essential enzymatic and mitogenic protein in trypanosomes) catalyzes the reversible conversion of l-proline to d-proline. We show the substrate-product analogue α-(hydroxymethyl)serine is a modest, linear mixed-type inhibitor of serine racemase from Schizosaccharomyces pombe (Ki=167±21mM, Ki'=661±81mM, cf. Km=19±2mM). The bicyclic substrate-product analogue of proline, 7-azabicyclo[2.2.1]heptan-7-ium-1-carboxylate is a weak inhibitor of proline racemase from Clostridium sticklandii, giving only 29% inhibition at 142.5mM. However, the more flexible bicyclic substrate-product analogue tetrahydro-1H-pyrrolizine-7a(5H)-carboxylate is a noncompetitive inhibitor of proline racemase from C. sticklandii (Ki=111±15mM, cf. Km=5.7±0.5mM). These results suggest that substrate-product analogue inhibitors of racemases may only be effective when the active site is capacious and/or plastic, or when the inhibitor is sufficiently flexible.
d-氨基酸可以作为生物体所需的特定生物合成构建块发挥重要作用，或者作为调节分子发挥作用。因此，催化 d-氨基酸形成的氨基酸消旋酶是潜在的治疗靶点。丝氨酸消旋酶催化 d-丝氨酸（神经递质的调节剂）从 l-丝氨酸的可逆形成，而脯氨酸消旋酶（锥虫中必需的酶和有丝分裂原蛋白）催化 l-脯氨酸到 d-脯氨酸的可逆转化。我们展示了底物-产物类似物 α-（羟甲基）丝氨酸是一种适度的、线性混合类型的丝氨酸消旋酶抑制剂，来自酿酒酵母（Ki=167±21mM，Ki'=661±81mM，与 Km=19±2mM 相比）。脯氨酸的双环底物-产物类似物，7-氮杂双环[2.2.1]庚烷-7-基-1-羧酸酯是来自 Clostridium sticklandii 的脯氨酸消旋酶的弱抑制剂，在 142.5mM 时仅抑制 29%。然而，更灵活的双环底物-产物类似物四氢-1H-吡咯嗪-7a(5H)-羧酸酯是来自 C. sticklandii 的脯氨酸消旋酶的非竞争性抑制剂（Ki=111±15mM，与 Km=5.7±0.5mM 相比）。这些结果表明，只有当活性位点宽敞和/或具有可塑性，或者当抑制剂足够灵活时，消旋酶的底物-产物类似物抑制剂才可能有效。
