EMR1, AN UNUSUAL MEMBER IN THE FAMILY OF HORMONE RECEPTORS WITH 7 TRANSMEMBRANE SEGMENTS

Proteins with seven transmembrane segments (7TM) define a superfamily of receptors (7TM receptors) sharing the same topology: an extracellul ar N-terminus, three extramembranous loops on either side of the plasm a membrane, and a cytoplasmic C-terminal tail. Upon ligand binding, cy toplasmic portions of the activated receptor interact with heterotrime ric G-coupled proteins to induce various second messengers. A small gr oup, recently recognized on the basis of homologous primary amino acid sequences, comprises receptors to hormones of the secretin/vasoactive intestinal peptide/glucagon family, parathyroid hormone and parathyro id hormone-related peptides, growth hormone-releasing factor, corticot ropin-releasing factor, and calcitonin. A cDNA, extracted from a neuro ectodermal cDNA library, was predicted to encode a new 886-amino-acid protein with three distinct domains. The C-terminal third contains the seven hydrophobic segments and characteristic residues that allow the protein to be readily aligned with the various hormone receptors in t he family. Six egf-like modules, at the N-terminus of the predicted ma ture protein, are separated from the transmembrane segments by a serin e/threonine-rich domain, a feature reminiscent of mucin like, single-s pan, integral membrane glycoproteins with adhesive properties. Because of its unique characteristics, this putative egf module-containing, m ucin-like hormone receptor has been named EMR1. Southern analysis of a panel of somatic cell hybrids and fluorescence in situ hybridization have assigned the EMR1 gene to human chromosome 19p13.3. (C) 1995 Acad emic Press, Inc,