Structural and genetic analysis of START superfamily protein MSMEG_0129 from Mycobacterium smegmatis

Abstract

Mycobacterium tuberculosis is a notorious pathogen that continues to threaten human health. Rv0164, an antigen of both T- and B cells conserved across mycobacteria, and MSMEG_0129, its close homolog in Mycobacterium smegmatis, are predicted members of the START domain superfamily, but their molecular function is unknown. Here, gene knockout studies demonstrate MSMEG_0129 is essential for bacterial growth, suggesting Rv0164 may be a potential drug target. The MSMEG_0129 crystal structure determined at 1.95 Å reveals a fold similar to that in polyketide aromatase/cyclases ZhuI and TcmN from Streptomyces sp. Structural comparisons and docking simulations, however, infer that MSMEG_0129 and Rv0164 are unlikely to catalyze polyketide aromatization/cyclization, but probably play an irreplaceable role during mycobacterial growth, for example, in lipid transfer during cell envelope synthesis.

Discovery of a role for the single START-domain protein Mtsp17 in transcriptional regulation

“…Elucidating the mechanism of essential genes will be bene t to the development of more effective vaccines and better drugs. Mtsp17 has many special features, including: (1) no homologs in other genus; (2) essentiality for mycobacterial growth; (3) no such enzymatic activity as other bacterial START family proteins. Here we illustrate that Mtsp17 is involved in gene regulatory networks and demonstrate for the rst time that START family protein with mono domain could regulate transcription in MSM.…”

“…There is no homologous sequence in other genus that shares more than 30% identity with MTB Mtsp17, thus Mtsp17 can be not only an anti-TB drug target but also a candidate immunogen for vaccine development. Although mtsp17 has been demonstrated as an essential gene in both Mycobacterium smegmatis (MSM) and MTB [3,4], its physiological function is presently unclear. Considering its essentiality and exclusiveness in the genus Mycobacterium, Mtsp17 needs more investigation which will introduce new insights into understanding the physiological properties of mycobacteria.…”

“…Mtsp17 folds as polyketide cyclases/aromatases (CYC/ARO) although they share sequence identity lower than 20% [3]. CYC/ARO are monofunctional enzymes in the Type II polyketide synthase (PKS) complexes and transform linear poly-β-ketone intermediates into aromatic polyketides [5].…”

“…PKS has yet been identi ed in mycobacteria while 21 Type I PKSs and three Type III have been annotated [6]. Structural comparisons and docking infer that Mtsp17 is likely not enzyme that catalyzes polyketide cyclization and aromatization [3]. Therefore Mtsp17 may play essential roles in mycobacteria by a mechanism different from CYC/ARO.…”

“…As mtsp17 knockout is lethal to MSM, a mtsp17 complemented strain (M0129C) was previously generated in which plasmid-encoded Mtsp17 is induced by tetracycline while the genomic mtsp17 gene is deleted [3]. In this study, RNA-sequencing (RNA-seq) based transcriptomics analysis was performed to obtain a global pro le of genes regulated by Mtsp17 in MSM.…”