title: Role of the intra-A-chain disulfide bond of insulin-like peptide 3 in binding and activation of its receptor, RXFP2.
abstract: INSL3 is a member of the insulin-IGF-relaxin superfamily and plays a key role in male fetal development and in adult germ cell maturation. It is the cognate ligand for RXFP2, a leucine-rich repeat containing G-protein coupled receptor. To date, and in contrast to our current knowledge of the key structural features that are required for the binding of INSL3 to RXFP2, comparatively little is known about the key residues that are required to elicit receptor activation and downstream cell signaling. Early evidence suggests that these are contained principally within the A-chain. To further explore this hypothesis, we have undertaken an examination of the functional role of the intra-A-chain disulfide bond. Using solid-phase peptide synthesis together with regioselective disulfide bond formation, two analogs of human INSL3 were prepared in which the intra-chain disulfide bond was replaced, one in which the corresponding Cys residues were substituted with the isosteric Ser and the other in which the Cys were removed altogether. Both of these peptides retained nearly full RXFP2 receptor binding but were devoid of cAMP activity (receptor activation), indicating that the intra-A-chain disulfide bond makes a significant contribution to the ability of INSL3 to act as an RXFP2 agonist. Replacement of the disulfide bond with a metabolically stable dicarba bond yielded two isomers of INSL3 that each exhibited bioactivity similar to native INSL3. This study highlights the critical structural role played by the intra-A-chain disulfide bond of INSL3 in mediating agonist actions through the RXFP2 receptor.
authors.affiliation: Howard Florey Institute, University of Melbourne, Victoria 3010, Australia.
authors.forename: Suode
authors.initials: S
authors.lastname: Zhang
authors.forename: Richard A
authors.initials: RA
authors.lastname: Hughes
authors.forename: Ross A D
authors.initials: RA
authors.lastname: Bathgate
authors.forename: Fazel
authors.initials: F
authors.lastname: Shabanpoor
authors.forename: M Akhter
authors.initials: MA
authors.lastname: Hossain
authors.forename: Feng
authors.initials: F
authors.lastname: Lin
authors.forename: Bianca
authors.initials: B
authors.lastname: van Lierop
authors.forename: Andrea J
authors.initials: AJ
authors.lastname: Robinson
authors.forename: John D
authors.initials: JD
authors.lastname: Wade
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001667:Binding, Competitive; D002942:Circular Dichroism; D000242:Cyclic AMP / Q000378:metabolism; D003553:Cystine / Q000737:chemistry*; D017930:Genes, Reporter; D057809:HEK293 Cells; D006801:Humans; D007328:Insulin / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism*; D007700:Kinetics; D008024:Ligands; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism*; D017433:Protein Structure, Secondary; D021122:Protein Subunits / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry; D011506:Proteins / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D014162:Transfection
chemical_list: D007328:Insulin; C084797:Leydig insulin-like protein; D008024:Ligands; D010455:Peptides; D021122:Protein Subunits; D011506:Proteins; C472867:RXFP2 protein, human; D043562:Receptors, G-Protein-Coupled; D003553:Cystine; D000242:Cyclic AMP