Characterization of peptide QRFP (26RFa) and its receptor from amphioxus, Branchiostoma floridae.

A peptide ending with RFamide (Arg-Phe-amide) was discovered independently by three different laboratories in 2003 and named 26RFa or QRFP. In mammals, a longer version of the peptide, 43 amino acids, was identified and found to bind to the orphan G protein-coupled receptor GPR103. We searched the genome database of Branchiostoma floridae (Bfl) for receptor sequences related to those that bind peptides ending with RFa or RYa (including receptors for NPFF, PRLH, GnIH, and NPY). One receptor clustered in phylogenetic analyses with mammalian QRFP receptors. The gene has 3 introns in Bfl and 5 in human, but all intron positions differ, implying that the introns were inserted independently. A QRFP-like peptide consisting of 25 amino acids and ending with RFa was identified in the amphioxus genome. Eight of the ten last amino acids are identical between Bfl and human. The prepro-QRFP gene in Bfl has one intron in the propeptide whereas the human gene lacks introns. The Bfl QRFP peptide was synthesized and the receptor was functionally expressed in human cells. The response was measured as inositol phosphate (IP) turnover. The Bfl QRFP peptide was found to potently stimulate the receptor's ability to induce IP turnover with an EC50 of 0.28nM. Also the human QRFP peptides with 26 and 43 amino acids were found to stimulate the receptor (1.9 and 5.1nM, respectively). Human QRFP with 26 amino acids without the carboxyterminal amide had dramatically lower potency at 1.3μM. Thus, we have identified an amphioxus QRFP-related peptide and a corresponding receptor and shown that they interact to give a functional response.