Suvarna K, Seah L, Bhattacherjee V, Bhattacharjee J K
Department of Microbiology, Miami University, Oxford, OH 45056, USA,
Curr Genet. 1998 Apr;33(4):268-75. doi: 10.1007/s002940050336.
The unique alpha-aminoadipate pathway for lysine biosynthesis is present only in fungi and involves eight enzyme steps. alpha-Aminoadipate semialdehyde dehydrogenase, commonly called alpha-aminoadipate reductase (AAR), catalyzes the conversion of alpha-aminoadipic acid to alpha-aminoadipic semialdehyde by a novel mechanism. Two genes, LYS2 and LYS5, encode the heterodimeric enzyme in Saccharomyces cerevisiae. The LYS2 gene of Candida albicans was shown to be contained in the 4.8-kb insert of the plasmid pCaLYS2. This plasmid complemented lys2 mutants of both S. cerevisiae and C. albicans. The S. cerevisiae and C. albicans Lys2(+) transformants exhibited 138% and 160% of wild-type AAR activity, respectively. The DNA-sequence analysis of the 4.8-kb region in plasmid pCaLYS2 and a PCR product from genomic DNA which overlapped with the 4.8-kb insert revealed a continuous ORF of 4173 nucleotides encoding 1391 amino-acid residues. The C. albicans LYS2 ORF exhibited 63.0% identity at the nucleotide level and 56.2% identity at the amino-acid level to the LYS2 gene of S. cerevisiae. The ORF is preceded by consensus sequences for the TATA-, CAAT- and GCN4-box elements. An S. cerevesiae-type transcription termination signal is seen in the 3' flanking region. The deduced amino-acid sequence revealed a motif for an AMP-binding site and also the highly conserved core sequences common to peptide antibiotic synthetases. The LYS2 mRNA and alpha-aminoadipate reductase activity were repressed to a higher level in YEPD-grown cells than in cells grown in the presence of lysine or minimal medium. Additionally, AAR was shown to be feedback-inhibited by lysine and the lysine analog, thialysine. The results of the present report reveal the molecular characteristics of the LYS2 gene of C. albicans, its homology to peptide antibiotic synthetases, its divergence from the LYS2 gene of S. cerevisiae, and the regulation of AAR in C. albicans.
赖氨酸生物合成的独特α-氨基己二酸途径仅存在于真菌中，涉及八个酶促步骤。α-氨基己二酸半醛脱氢酶，通常称为α-氨基己二酸还原酶（AAR），通过一种新机制催化α-氨基己二酸转化为α-氨基己二酸半醛。LYS2和LYS5这两个基因在酿酒酵母中编码异二聚体酶。白色念珠菌的LYS2基因被证明包含在质粒pCaLYS2的4.8 kb插入片段中。该质粒可互补酿酒酵母和白色念珠菌的lys2突变体。酿酒酵母和白色念珠菌的Lys2(+)转化体分别表现出野生型AAR活性的138%和160%。对质粒pCaLYS2中4.8 kb区域的DNA序列分析以及来自基因组DNA且与4.8 kb插入片段重叠的PCR产物显示，有一个4173个核苷酸的连续开放阅读框，编码1391个氨基酸残基。白色念珠菌的LYS2开放阅读框在核苷酸水平上与酿酒酵母的LYS2基因有63.0%的同一性，在氨基酸水平上有56.2%的同一性。该开放阅读框之前有TATA盒、CAAT盒和GCN4盒元件的共有序列。在3'侧翼区域可见一个酿酒酵母型转录终止信号。推导的氨基酸序列揭示了一个AMP结合位点的基序以及肽抗生素合成酶共有的高度保守的核心序列。与在赖氨酸或基本培养基存在下生长的细胞相比，在YEPD培养基中生长的细胞中，LYS2 mRNA和α-氨基己二酸还原酶活性被抑制到更高水平。此外，AAR被证明受到赖氨酸和赖氨酸类似物硫赖氨酸的反馈抑制。本报告的结果揭示了白色念珠菌LYS2基因的分子特征、其与肽抗生素合成酶的同源性、其与酿酒酵母LYS2基因 的差异以及白色念珠菌中AAR的调控。
