Crystal structure of LGR ligand α2/β5 from Caenorhabditis elegans with implications for the evolution of glycoprotein hormones

Abstract

A family of leucine-rich-repeat-containing G-protein-coupled receptors (LGRs) mediate diverse physiological responses when complexed with their cognate ligands. LGRs are present in all metazoan animals. In humans, the LGR ligands include glycoprotein hormones (GPHs) chorionic gonadotropin (hCG), luteinizing hormone, follicle-stimulating hormone (hFSH), and thyroid-stimulating hormone (hTSH). These hormones are αβ heterodimers of cystine-knot protein chains. LGRs and their ligand chains have coevolved. Ancestral hormone homologs, present in both bilaterian animals and chordates, are identified as α2β5. We have used single-wavelength anomalous diffraction and molecular replacement to determine structures of the α2β5 hormone from Caenorhabditis elegans ( Ce α2β5). Ce α2β5 is unglycosylated, as are many other α2β5 hormones. Both Hs α2β5, the human homolog of Ce α2β5, and hTSH activate the same receptor (hTSHR). Despite having little sequence similarity to vertebrate GPHs, apart from the cysteine patterns from core disulfide bridges, Ce α2β5 is generally similar in structure to these counterparts; however, its α2 and β5 subunits are more symmetric as compared with α and β of hCG and hFSH. This quasisymmetry suggests a hypothetical homodimeric antecedent of the α2β5 and αβ heterodimers. Known structures together with AlphaFold models from the sequences for other LGR ligands provide representatives for the molecular evolution of LGR ligands from early metazoans through the present-day GPHs. The experimental Ce α2β5 structure validates its AlphaFold model, and thus also that for Hs α2β5; and interfacial characteristics in a model for the Hs α2β5:hTSHR complex are similar to those found in an experimental hTSH:hTSHR structure.

Ancestral glycoprotein hormone-receptor pathway controls growth in C. elegans

“…Phylogenetic analyses also revealed orthologs of the thyrostimulin GPA2 and GPB5 subunits in the C. elegans genome ( 9 , 15 , 21 , 40 ), which carry a cysteine knot motif of six cysteine residues that is typical of glycoprotein hormone subunits ( 44 , 45 ). Recent analysis of the crystal structure of C. elegans GPA2/GPB5 validates its structural similarity to vertebrate glycoprotein hormones that was previously found by comparative genomic analyses ( 3 , 8 , 46 ). In addition, C. elegans has only one receptor ortholog of the vertebrate glycoprotein hormone receptors.…”

Evolutionary conserved peptide and glycoprotein hormone-like neuroendocrine systems in C. elegans

“…Heterodimerization of GPLA-1 and GPLB-1 might thus not be essential for activating the receptor. This is in line with crystal structure analysis, which demonstrates high similarity between C. elegans GPLA-1 and GPLB-1, suggesting that thyrostimulin-like subunits might have evolved from a monomeric or homodimeric ancestral hormone ( Gong et al, 2023 ). Several theories on the evolutionary origin of glycoprotein hormone subunits have previously suggested that the ancestral thyrostimulin subunits arose in early metazoans from a single mono- or homodimeric antecedent that contained an α- or β-like structure ( Gong et al, 2023 ; Park et al, 2005 ; Roch and Sherwood, 2014 ).…”

“…In many of the reported FSHR-1 functions, details concerning its interaction partner(s) are lacking because ligands of FSHR-1 were identified only recently ( Kenis et al, 2023 ). Like other invertebrates, C. elegans has single orthologs of GPA2 and GPB5, named glycoprotein hormone-like alpha 1 (GPLA-1) and -beta 1 (GPLB-1) ( Gong et al, 2023 ; Hsu et al, 2002 ; Kenis et al, 2023 ; Oishi et al, 2009 ). GPLA-1/GPLB-1 act as cognate ligands of FSHR-1 in vivo and activate FSHR-1 in cultured cells, stimulating cAMP signaling ( Kenis et al, 2023 ; Kudo et al, 2000 ; Wang et al, 2023 ).…”

An ancient thyrostimulin-like neuroendocrine pathway regulates growth inCaenorhabditis elegans

“…Phylogenetic analyses show a clear conservation of thyrostimulin GPA2 and GPB5 polypeptides across Protostomia and Deuterostomia, but their physiological roles remain elusive [7][8][9]14,26,29,46 . In invertebrates, GPA2/GPB5 orthologs have only been functionally characterized in arthropods 12,[38][39][40] .…”

“…Here, we show that C. elegans FSHR-1 is activated by GPLA-1/GPLB-1 as well as individual GPLA-1 and GPLB-1 polypeptides. Recent analyses of the crystal structure of GPLA-1/GPLB-1 revealed that the two subunits indeed heterodimerize but are also more symmetric in structure as compared to the alpha and beta subunits of human CG and FSH 46 . Our results are in line with this study.…”