In molecular biology the PIN domain is a
protein domain
In molecular biology, a protein domain is a region of a protein's polypeptide chain that is self-stabilizing and that folds independently from the rest. Each domain forms a compact folded three-dimensional structure. Many proteins consist of s ...
that is about 130 amino acids in length. PIN domains function as
nuclease
A nuclease (also archaically known as nucleodepolymerase or polynucleotidase) is an enzyme capable of cleaving the phosphodiester bonds between nucleotides of nucleic acids. Nucleases variously effect single and double stranded breaks in their ta ...
enzymes that cleave
single stranded RNA in a sequence- or structure-dependent manner.
PIN domains contain four nearly invariant acidic residues.
Crystal structures show these residues clustered together in the putative
active site
In biology and biochemistry, the active site is the region of an enzyme where substrate molecules bind and undergo a chemical reaction. The active site consists of amino acid residues that form temporary bonds with the substrate (binding site) a ...
. In eukaryotes PIN domains are found in proteins involved in
nonsense mediated mRNA decay, in proteins such as
SMG5
Protein SMG5 is a protein that in humans is encoded by the ''SMG5'' gene
In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ...
and
SMG6
Telomerase-binding protein EST1A is an enzyme that in humans is encoded by the ''SMG6'' gene on chromosome 17. It is ubiquitously expressed in many tissues and cell types. The C-terminus of the EST1A protein contains a PilT N-terminus (PIN) domai ...
, and in processing of 18S
ribosomal RNA
Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA which is the primary component of ribosomes, essential to all cells. rRNA is a ribozyme which carries out protein synthesis in ribosomes. Ribosomal RNA is transcribed from ribosomal ...
. The majority of PIN-domain proteins found in prokaryotes are the toxic components of
toxin-antitoxin operons.
These loci provide a control mechanism that helps free-living prokaryotes cope with nutritional stress.
References
{{Reflist
Protein domains