Lutropin-Choriogonadotropin Receptor: An Unusual Member of the G Protein-Coupled Receptor Family

TLDR

The rat luteal luteinizing hormone–chorionic gonadotropin receptor (LH‑CG‑R) is a 26‑residue signal peptide followed by a 341‑residue leucine‑rich repeat extracellular domain and a 333‑residue seven‑transmembrane region, showing sequence similarity to G protein‑coupled receptors and suggesting it arose by recombination of LRG and GPCR genes. A complementary DNA (cDNA) for the rat luteal LH‑CG‑R was isolated using a PCR‑generated DNA probe based on peptide sequences of purified receptor protein. Cells engineered to express LH‑CG‑R cDNA bind human choriogonadotropin with high affinity and show increased cyclic AMP upon hormone exposure, and RNA blot analysis and in situ hybridization reveal that the 4.4‑kb mRNA is prominently localized in the rat ovary.

Abstract

A complementary DNA (cDNA) for the rat luteal lutropin-choriogonadotropin receptor (LH-CG-R) was isolated with the use of a DNA probe generated in a polymerase chain reaction with oligonucleotide primers based on peptide sequences of purified receptor protein. As would be predicted from the cDNA sequence, the LH-CG-R consists of a 26-residue signal peptide, a 341-residue extracellular domain displaying an internal repeat structure characteristic of members of the leucine-rich glycoprotein (LRG) family, and a 333-residue region containing seven transmembrane segments. This membrane-spanning region displays sequence similarity with all members of the G protein-coupled receptor family. Hence, the LH-CG-R gene may have evolved by recombination of LRG and G protein-coupled receptor genes. Cells engineered to express LH-CG-R cDNA bind human choriogonadotropin with high affinity and show an increase in cyclic adenosine monophosphate when exposed to hormone. As revealed by RNA blot analysis and in situ hybridization, the 4.4-kilobase cognate messenger RNA is prominently localized in the rat ovary.