| Literature References | 1. NORTH, R.A.
Families of ion channels with two hydrophobic segments.
CURR.OPIN.CELL BIOL. 8 474-483 (1996).
2. MACKENZIE, A.B., SURPRENANT, A. AND NORTH, R.A.
Functional and molecular diversity of purinergic ion channel receptors.
ANN.N.Y.ACAD.SCI. 868 716-729 (1999).
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| Documentation | P2X purinoceptors are cell membrane ion channels, gated by adenosine
5'-triphosphate (ATP) and other nucleotides. They have been found to be
widely expressed on mammalian cells, and, by means of their functional
properties, can be differentiated into three sub-groups. The first group is
almost equally well activated by ATP and its analogue alphabetamethyleneATP,
whereas, the second group is not activated by the latter compound. A third
type of receptor (also called P2Z) is distinguished by the fact that
repeated or prolonged agonist application leads to the opening of much
larger pores, allowing large molecules to traverse the cell membrane. This
increased permeability rapidly leads to cell death, and lysis.
Molecular cloning studies have identified seven P2X receptor subtypes,
designated P2X1-P2X7. These receptors are proteins that share 35-48% amino
acid identity, and possess two putative transmembrane (TM) domains,
separated by a long (~270 residues) intervening sequence, which is
thought to form an extracellular loop. Around 1/4 of the residues within
the loop are invariant between the cloned subtypes, including 10
characteristic cysteines.
Studies of the functional properties of heterologously expressed P2X
receptors, together with the examination of their distribution in native
tissues, suggests they likely occur as both homo- and heteromultimers
in vivo [1,2].
The P2X5 receptor (along with P2X2, P2X4 and P2X6) falls into a group of
receptors that are sensitive to ATP, but not alphabetamethyleneATP. Splice
variants of P2X5 have been detected [2].
P2X5RECEPTOR is a 4-element fingerprint that provides a signature for the
P2X purinoceptor isoform 5. The fingerprint was derived from an initial
alignment of 2 sequences: the motifs were drawn from conserved regions
spanning virtually the full alignment length, focusing on those sections
that characterise the P2X purinoceptor isoform 5 but distinguish it from
others - motif 1 resides within the putative cytoplasmic N-terminus; and
motifs 2-4 lie within the exoplasmic loop connecting the two putative TM
domains. Two iterations on SPTR37_10f were required to reach convergence,
at which point a true set comprising 3 sequences was identified.
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