There exist at least 30 human G-protein-coupled receptors with long Ser/Thr-rich N-termini.
We report six novel members of the superfamily of human G-protein coupled receptors (GPCRs) found by searches in the human genome databases, termed GPR123, GPR124, GPR125, GPR126, GPR127, and GPR128. Phylogenetic analysis demonstrates that these are additional members of the family of GPCRs with long N-termini, previously termed EGF-7TM, LNB-7TM, B2 or LN-7TM, showing that there exist at least 30 such GPCRs in the human genome. Three of these receptors form their own phylogenetic cluster, while two other places in a cluster with the previously reported HE6 and GPR56 (TM7XN1) and one with EMR1-3. All the novel receptors have a GPS domain in their N-terminus, except GPR123, as well as long Ser/Thr rich regions forming mucin-like stalks. GPR124 and GPR125 have a leucine rich repeat (LRR), an immunoglobulin (Ig) domain, and a hormone-binding domain (HBD). The Ig domain shows similarities to motilin and titin, while the LRR domain shows similarities to LRIG1 and SLIT1-2. GPR127 has one EGF domain while GPR126 and GPR128 do not contain domains that are readily recognized in other proteins beyond the GPS domain. We found several human EST sequences for most of the receptors showing differential expression patterns, which may indicate that some of these receptors participate in central functions while others are more likely to have a role in the immune or reproductive systems.