5uct | pdb_00005uct
Mycobacterium tuberculosis toxin MazF-mt6
Structural highlights
Function[MAZF3_MYCTU] Toxic component of a type II toxin-antitoxin (TA) module. Acts as an mRNA and 23S rRNA interferase, cleaving predominantly after the first 2 Us in the sequence 5'-UUCCU-3'; in 23S rRNA only cleaves once in the ribosomal A site in dissociated but not intact ribosomes. Cleavage of 23S rRNA inhibits protein translation; the 23S rRNA region cleaved is involved in tRNA-binding in the A site, 30S and 50S subunit interaction and ribosome recycling factor association (PubMed:23650345). Upon expression in E.coli and M.smegmatis inhibits cell growth and colony formation. It dramatically increases persister cell formation in M.smegmatis upon challenge with gentamicin or kanamycin. Overexpression leads to bacteriostasis rather than bacteriocide. Its toxic effect is neutralized by coexpression with cognate antitoxin MazE3.[1] [2] [3] [4] [5] [6] Publication Abstract from PubMedToxin-antitoxin systems are ubiquitous in prokaryotic and archaea genomes and regulate growth in response to stress. E. coli contains at least 36 putative toxin-antitoxin gene pairs, and some pathogens such as Mycobacterium tuberculosis (Mtb) have over 90 toxin-antitoxin operons. E. coli MazF cleaves free mRNA after encountering stress and nine Mtb MazF family members cleave mRNA, tRNA, or rRNA. Moreover, Mtb MazF-mt6 cleaves 23S rRNA Helix 70 to inhibit protein synthesis. The overall tertiary folds of these MazFs are predicted to be similar, therefore it is unclear how they recognize structurally distinct RNAs. Here we report the 2.7 A X-ray crystal structure of MazF-mt6. MazF-mt6 adopts a PemK-like fold, but lacks an elongated beta1-beta2 linker, a region that typically acts as a gate to direct RNA or antitoxin binding. In the absence of an elongated beta1-beta2 linker, MazF-mt6 is unable to transition between open and closed states, suggesting that the regulation of RNA or antitoxin selection may be distinct from that in canonical MazFs. Additionally, a shortened beta1-beta2 linker allows for the formation of a deep, solvent accessible, active-site pocket which may allow recognition of specific, structured RNAs like H70. Structure-based mutagenesis and bacterial growth experiments demonstrate that MazF-mt6 residues Arg-13, Asp-10, and Thr-36 are critical for RNase activity and likely catalyze the proton-relay mechanism for RNA cleavage. These results provide further critical insights into how MazF secondary structural elements adapt to recognize diverse RNA substrates. The structure and function of Mycobacterium tuberculosis MazF-mt6 provides insights into conserved features of MazF endonucleases.,Hoffer ED, Miles SJ, Dunham CM J Biol Chem. 2017 Mar 15. pii: jbc.M117.779306. doi: 10.1074/jbc.M117.779306. PMID:28298445[7] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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