VapC-like PIN domain of Saccharomyces cerevisiae Swt1p, human SWT1 and related proteins
Saccharomyces cerevisiae mRNA-processing endoribonuclease Swt1p plays an important role in quality control of nuclear mRNPs in eukaryotes. Human transcriptional protein SWT1 (RNA endoribonuclease homolog, also known as HsSwt1, C1orf26, and chromosome 1 open reading frame 26) is an RNA endonuclease that participates in quality control of nuclear mRNPs and can associate with the nuclear pore complex (NPC). This subfamily belongs to the Smg5 and Smg6-like PIN domain family. Smg5 and Smg6 are essential factors in NMD, a post-transcriptional regulatory pathway that recognizes and rapidly degrades mRNAs containing premature translation termination codons. In vivo, the Smg6 PIN domain elicits degradation of bound mRNAs, as well as, metal-ion dependent, degradation of single-stranded RNA, in vitro. The PIN (PilT N terminus) domain belongs to a large nuclease superfamily. The structural properties of the PIN domain indicate its putative active center, consisting of invariant acidic amino acid residues (putative metal-binding residues), is geometrically similar in the active center of structure-specific 5' nucleases (also known as Flap endonuclease-1-like), PIN-domain ribonucleases of eukaryotic rRNA editing proteins, and bacterial toxins of toxin-antitoxin (TA) operons. Point mutation studies of the conserved aspartate residues in the catalytic center of the Smg6 PIN domain revealed that Smg6 is the endonuclease involved in human NMD. However, Smg5 lacks several of these key catalytic residues and does not degrade single-stranded RNA, in vivo.
Comment:based on structure and experimental evidence from PIN-superfamily members belonging to the FEN-like, VapC-like, PRORP-like, and LabA-like families
Comment:The PIN domain superfamily contains three highly conserved catalytic residues which coordinate metal ions; in some members, additional metal coordinating residues can be found while some others lack several of these key catalytic residues. In this subgroup 5 conserved catalytic residues are found.
Comment:Note that SMG5, a related VapC-like family member, lacks all but a single aspartic acid residue in the active site and consequently is inactive as a nuclease
Jiyao W et al.(2023). "The conserved domain database in 2023.",