The Oncogenic Role of γ-Aminobutyrate Aminotransferase in Human Tumor: A Pan-Cancer Analysis

Emerging evidence supports the correlation between γ-aminobutyrate aminotransferase (ABAT) and tumors, but few research groups used pan-cancer analysis to verify it previously. Therefore, this study used the Cancer Genome Atlas (TCGA) database and the Gene Expression Omnibus (GEO) to obtain information about the correlations between ABAT and tumor development, and to explore its potential effectiveness for genetic alterations in tumor prognosis. The reduced expression level of ABAT in a majority of tumors is significantly associated with the poor prognosis. The genetic alteration of ABAT seems linked to the favorable prognosis of Uterine Corpus Endometrial Carcinoma (UCEC). Immune infiltration analysis showed a significantly positive correlation between ABAT and cancer-associated fibroblasts in the majority of tumors, but a highly negative correlation with Kidney renal clear cell carcinoma (KIRC), Kidney Renal Papillary cell carcinoma (KIRP), and Prostate adenocarcinoma (PRAD). Enrichment analysis showed that cell junction organization, amino acids metabolism, and neuronal system-involved behaviors might affect the pathogenesis or etiology of cancer. This study is the first pan-cancer analysis that offers a detailed, comprehensive study of the process of the oncogenic roles of ABAT across different human tumors.

Characterization of a novel moderate-substrate specificity amino acid racemase from the hyperthermophilic archaeon Thermococcus litoralis

The amino acid sequence of the OCC_10945 gene product from the hyperthermophilic archaeon Thermococcus litoralis DSM5473, originally annotated as γ-aminobutyrate aminotransferase, is highly similar to that of the uncharacterized pyridoxal 5ʹ-phosphate (PLP)-dependent amino acid racemase from Pyrococcus horikoshii. The OCC_10945 enzyme was successfully overexpressed in Escherichia coli by co-expression with a chaperone protein. The purified enzyme demonstrated PLP-dependent amino acid racemase activity primarily toward Met and Leu. Although PLP contributed to enzyme stability, it only loosely bound to this enzyme. Enzyme activity was strongly inhibited by several metal ions, including Co2+ and Zn2+, and non-substrate amino acids such as l-Arg and l-Lys. These results suggest that the underlying PLP-binding and substrate recognition mechanisms in this enzyme are significantly different from those of the other archaeal and bacterial amino acid racemases. This is the first description of a novel PLP-dependent amino acid racemase with moderate substrate specificity in hyperthermophilic archaea.