Studies of physiological function of D-aspartate in eukaryotic cells : from yeasts to mammals

我们研究了编码D-氨基酸相关酶的真核基因的功能。结果表明，裂殖酵母的DAO 1^+、ALR 1^+、ALR 2^+和SRF1^+分别编码D-氨基酸氧化酶、丙氨酸消旋酶、精氨酸消旋酶和丝氨酸消旋酶。酿酒酵母细胞中含有D-氨基酸N-乙酰转移酶，但其基因尚不清楚。我们发现该酶是由组蛋白/蛋白乙酰转移酶基因HPA3编码的，该基因属于GCN5相关的N-乙酰转移酶超家族。基因产物Hpa3p作用于多种D-氨基酸，但不作用于L氨基酸。Hpa3p与酵母组蛋白乙酰转移酶Hpa2p有49%的序列同源性和81%的序列相似性。然而，Hpa3p几乎没有组蛋白乙酰转移酶活性，Hpa2p除了对D-赖氨酸和L-赖氨酸有微量活性外，对D-或L-氨基酸没有检测到乙酰转移酶活性。动力学分析表明，Hpa3p以有序的bi-bi机制催化D-氨基酸的乙酰化反应，其中乙酰辅酶A是第一个结合的底物，辅酶A是最后一个离开的产物。Hpa3p被发现参与降低各种D-氨基酸的抑制效应。我们还研究了小鼠PROSC蛋白的功能，它是酿酒酵母Yb1036cp的同源物，它没有序列同源性，但具有与细菌丙氨酸消旋酶N-末端结构相似的三维结构。

We studied functions of the eukaryotic genes encoding putative D-amino acid-related enzymes. We found that dao 1^+, alr 1^+, alr 2^+, and srf1^+ of Schizosaccharomyces pombe encode D-amino acid oxidase, alanine racemase, arginine racemase, and serine racemase, respectively. Saccharomyces cerevisiae cells were reported to contain D-amino acid N-acetyltransferase, however its gene has been unknown. We found that the enzyme is encoded by HPA3, the gene of a putative histone/protein acetyltransferase belonging to Gcn5-related N-acetyltransferase superfamily. The gene product, Hpa3p, acts on a wide range of D-amino acids but none of L-amino acids. Hpa3p shares 49% sequence identity and 81% sequence similarity with Hpa2p, a yeast histone acetyltransferase. However, Hpa3p shows little histone acetyltransferase activity, and Hpa2p has no detectable acetyltransferase activities towards D-or L-amino acids tested except for the trace activity towards D-and L-lysine. Kinetic analyses suggest that Hpa3p catalyzes the acetylation of D-amino acids with an ordered bi-bi mechanism, in which acetyl-CoA is the first substrate to be bound and CoA is the last product to leave. Hpa3p was revealed to be involved in lowering the inhibitoru effect of various D-amino acids. We also studied the function of the mouse PROSC protein, a homolog of S. cerevisiae Yb1036cp, which has no sequencial homology but has similar three-dimensional structure to that of the N-terminal domain of bacterial alanine racemase.