Abstract
G-protein coupled receptors form a large superfamily of plasma membrane proteins which serve a variety of signal transduction roles. New receptors continue to be identified. Based on sequence homology the superfamily can currently be divided into three families, the rhodopsin family which includes the vast majority of identified receptors, and the secretin and metabotropic glutamate receptor families which share a general architecture with each other and the rhodopsin family but no obvious sequence identity. Screening for additional members of the secretin family led to the identification of the parathyroid hormone-2 (PTH2) receptor. Ligand recognition by the PTH2 receptor partially overlaps that of the PTH/parathyroid hormone-related peptide (PTHrP) receptor. This has facilitated structure-function analysis of ligands for these receptors. The physiological role of the PTH2 receptor is under investigation but its distribution suggests that it may be a neurotransmitter receptor and could participate in modulation of a number of organ systems. The relative abundance of PTH2 receptor mRNA in the brain and the inability to detect mRNA encoding PTH, its only currently identified ligand, suggest the existence of another endogenous ligand, for which evidence has recently been obtained.
Highlights
G-protein coupled receptors are important mediators of intercellular communication throughout the body
The parathyroid hormone-2 (PTH2) receptor was identified by the degenerate primer PCR approach, and the full cDNA sequence obtained by a combination of hybridization, using the initial PCR fragment as a probe, and the RACE technique (Usdin et al, 1995)
The presence of PTH2 receptor mRNA in each of these areas suggests that it may be involved in modulation the specific functions of these tissues, but it is possible that it is involved in more general metabolic responses
Summary
G-protein coupled receptors are important mediators of intercellular communication throughout the body. Following identification of the secretin, calcitonin, and PTH/PTHrP receptors by functional expression (Ishihara et al, 1991; Jüpner et al, 1991; Lin et al, 1991) it became apparent that these receptors were members of a distinct protein family. The amino acid sequence of the PTH2 receptor is approximately 50% identical to that of th PTH/PTHrP receptor (Figure 1) and is somewhat less similar to other members of the secretin receptor family.
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