InterPro domain: IPR029060

PIN domains are small protein domains identified by the presence of three strictly conserved acidic residues. Apart from these three residues, there is poor sequence conservation [ 1 ]. PIN domains are found in eukaryotes, eubacteria and archaea. In eukaryotes they are ribonucleases involved in nonsense mediated mRNA decay [ 2 ] and in processing of 18S ribosomal RNA [ 3 ]. In prokaryotes, they are the toxic components of toxin-antitoxin (TA) systems, their toxicity arising by virtue of their ribonuclease activity. The PIN domain TA systems are now called VapBC TAs(virulence associated proteins), where VapB is the inhibitor and VapC, the PIN-domain ribonuclease toxin [ 4 ].

This superfamily represents a domain sharing protein structural similarity with the PIN domain. This domain can also be found in the N-terminal of the 5'3'-exonuclease, which has a 3-layer alpha/beta/alpha core structure and contains an alpha-helical arch [ 4 ].

1. The PIN-domain ribonucleases and the prokaryotic VapBC toxin-antitoxin array. Protein Eng. Des. Sel. 24, 33-40
2. Structures of the PIN domains of SMG6 and SMG5 reveal a nuclease within the mRNA surveillance complex. EMBO J. 25, 5117-25
3. Nob1 binds the single-stranded cleavage site D at the 3'-end of 18S rRNA with its PIN domain. Proc. Natl. Acad. Sci. U.S.A. 106, 14259-64
4. A helical arch allowing single-stranded DNA to thread through T5 5'-exonuclease. Nature 382, 90-3