Evolution of Membrane Bound Proteins and their Ligands : The Melanocortin (MC) Receptor Inverse Agonists AgRP2, ASIP2, Drug/Metabolite Transporters, and SPNS1

Abstract: Integral membrane proteins play a key role hormonal and neuronal signaling. Transmembrane helix (TM) proteins form about 27% of the human proteome. Furthermore, 44% of the human drug targets are receptors, and 19% of these are seven-transmembrane domain receptors (GPCRs), which constitute 4% of the entire protein-coding genome. After receptors, solute carriers (SLCs) constitute the second largest superfamily of TM proteins. Three of the largest SLC families contain protein domains that are members of the drug/metabolite transporter clan.We present evidence that the drug/metabolite transporter (DMT) families have evolved from a domain duplication event before the radiation of Viridiplantae in the EamA family (previously called domain unknown function 6). We present evidence that the family called fatty acid elongases are homologous to transporters, not enzymes as had previously been thought. We renamed several transporters, and introduced the new HGNC-approved nomenclature of SLC35G1 – 6.We show the presence of AgRP and ASIP in elephant shark, a cartilaginous fish belonging to the subclass of Holocephali. However, we do not find any of these genes in lamprey or lancelet, suggesting that the MCA and MCB receptors function without antagonists in lamprey.We report that a venom peptide in Plectreurys tristis has the same cysteine knot structure as fish AgRP2, a higher similarity than previously known. Here we suggest that the Agouti-like peptide genes were formed through classical subsequent gene duplications where the AgRP is likely to be the most ancestral, first splitting from a common ancestor to ASIP and A2. We introduce a new technique for synteny detection, sinusoidal Hough transform.We found that the known obesity SNPs in SH2B1, rs4788102 (p=0.0023) and rs7498665 (p=0.0018) were associated with triglyceride levels in the North Swedish Population Health Study (NSPHS) cohort, consisting of 719 individuals from the Karesuando parish in northern Sweden. To account for kinship, the SH2B1 SNPs, and four SNPs in the expanded region were analyzed for association with triglyceride levels using SOLAR. We found a stronger signal (p=0.0009) for a SNP, near SH2B1, rs8045689, located in an intron of SPNS1 which is structurally similar to a sphingolipid transporter.