title: Molecular and functional analysis of human β-defensin 3 action at melanocortin receptors.
abstract: The β-defensins are a class of small, cationic proteins first recognized as antimicrobial components of the innate and adaptive immune system. More recently, one of the major β-defensins produced in skin, β-defensin 3, has been discovered to function as a melanocortin receptor ligand in vivo and in vitro, but its biophysical and pharmacological basis of action has been enigmatic. Here, we report functional and biochemical studies focused on human β-defensin 3 (HBD3) and melanocortin receptors 1 and 4. Genetic and pharmacologic studies indicate that HBD3 acts as a neutral melanocortin receptor antagonist capable of blocking the action of either stimulatory agonists such as α-melanocyte stimulating hormone or inhibitory inverse agonists such as Agouti signaling protein (ASIP) and Agouti-related protein (AGRP). A comprehensive structure-function analysis demonstrates that two patches of positively charged residues, located on opposite poles of HBD3 and spatially organized by the compact β-defensin fold, are primarily responsible for high-affinity binding to melanocortin receptors. These findings identify a distinct mode of melanocortin receptor-ligand interactions based primarily on electrostatic complementarity, with implications for designing ligands that target melanocortin and potentially other seven transmembrane receptors.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Santa Cruz, Santa Cruz, CA 95064, USA.
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Nix
authors.forename: Christopher B
authors.initials: CB
authors.lastname: Kaelin
authors.forename: Tina
authors.initials: T
authors.lastname: Ta
authors.forename: Allison
authors.initials: A
authors.lastname: Weis
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Morton
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Barsh
authors.forename: Glenn L
authors.initials: GL
authors.lastname: Millhauser
mesh_terms: D054366:Agouti Signaling Protein / Q000819:agonists / Q000235:genetics / Q000378:metabolism; D054369:Agouti-Related Protein / Q000819:agonists / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D006801:Humans; D008024:Ligands; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D044102:Receptor, Melanocortin, Type 1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D044105:Receptor, Melanocortin, Type 4 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D055672:Static Electricity; D023083:beta-Defensins / Q000235:genetics / Q000378:metabolism*
chemical_list: D054366:Agouti Signaling Protein; D054369:Agouti-Related Protein; C422950:DEFB103A protein, human; D008024:Ligands; C470072:MC4R protein, human; D044102:Receptor, Melanocortin, Type 1; D044105:Receptor, Melanocortin, Type 4; D023083:beta-Defensins