S
IPR020612

Methylthiotransferase, conserved site

InterPro entry
Short nameMethylthiotransferase_CS

Description

The methylthiotransferase (MTTase) or miaB-like family is named after the (dimethylallyl)adenosine tRNA MTTase miaB protein, which catalyses a C-H to C-S bond conversion in the methylthiolation of tRNA. A related bacterial enzyme rimO performs a similar methylthiolation, but on a protein substrate. RimO acts on the ribosomal protein S12 and forms a separate MTTase subfamily. The miaB-subfamily includes mammalian CDK5 regulatory subunit-associated proteins and similar proteins in other eukaryotes. Two other subfamilies, yqeV and CDKAL1, are named after a Bacillus subtilis and a human protein, respectively. While yqeV-like proteins are found in bacteria, CDKAL1 subfamily members occur in eukaryotes and in archaebacteria. The likely MTTases from these 4 subfamilies contain an N-terminal MTTase domain, a central radical generating fold and a C-terminal TRAM domain (see
[prositedoc:PDOC50926]
). The core forms a radical SAM fold (or AdoMet radical), containing a cysteine motif CxxxCxxC that binds a [4Fe-4S] cluster
[1, 2, 3]
. A reducing equivalent from the [4Fe-4S]+ cluster is used to cleave S-adenosylmethionine (SAM) to generate methionine and a 5'-deoxyadenosyl radical. The latter is thought to produce a reactive substrate radical that is amenable to sulphur insertion
[2, 3]
. The N-terminal MTTase domain contains 3 cysteines that bind a second [4Fe-4S] cluster, in addition to the radical-generating [4Fe-4S] cluster, which could be involved in the thiolation reaction. The C-terminal TRAM domain is not shared with other radical SAM proteins outside the MTTase family. The TRAM domain can bind to RNA substrate and seems to be important for substrate recognition. The tertiary structure of the central radical SAM fold has six β/α motifs resembling a three-quarter TIM barrel core (see
[prositedoc:PDOC00155]
)
[4]
. The N-terminal MTTase domain might form an additional [β/α]2 TIM barrel unit
[2]
.

This entry represents a conserved site containing three of the conserved cysteines that form the motif in the central radical SAM fold.

References

1.Enzymatic modification of tRNAs: MiaB is an iron-sulfur protein. Pierrel F, Bjork GR, Fontecave M, Atta M. J. Biol. Chem. 277, 13367-70, (2002). View articlePMID: 11882645

2.RimO, a MiaB-like enzyme, methylthiolates the universally conserved Asp88 residue of ribosomal protein S12 in Escherichia coli. Anton BP, Saleh L, Benner JS, Raleigh EA, Kasif S, Roberts RJ. Proc. Natl. Acad. Sci. U.S.A. 105, 1826-31, (2008). View articlePMID: 18252828

3.Radical SAM, a novel protein superfamily linking unresolved steps in familiar biosynthetic pathways with radical mechanisms: functional characterization using new analysis and information visualization methods. Sofia HJ, Chen G, Hetzler BG, Reyes-Spindola JF, Miller NE. Nucleic Acids Res. 29, 1097-106, (2001). View articlePMID: 11222759

4.AdoMet radical proteins--from structure to evolution--alignment of divergent protein sequences reveals strong secondary structure element conservation. Nicolet Y, Drennan CL. Nucleic Acids Res. 32, 4015-25, (2004). View articlePMID: 15289575

GO terms

biological process

  • None

cellular component

  • None

Cross References

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