title: Electrostatic Similarity Analysis of Human β-Defensin Binding in the Melanocortin System.
abstract: The β-defensins are a class of small cationic proteins that serve as components of numerous systems in vertebrate biology, including the immune and melanocortin systems. Human β-defensin 3 (HBD3), which is produced in the skin, has been found to bind to melanocortin receptors 1 and 4 through complementary electrostatics, a unique mechanism of ligand-receptor interaction. This finding indicates that electrostatics alone, and not specific amino acid contact points, could be sufficient for function in this ligand-receptor system, and further suggests that other small peptide ligands could interact with these receptors in a similar fashion. Here, we conducted molecular-similarity analyses and functional studies of additional members of the human β-defensin family, examining their potential as ligands of melanocortin-1 receptor, through selection based on their electrostatic similarity to HBD3. Using Poisson-Boltzmann electrostatic calculations and molecular-similarity analysis, we identified members of the human β-defensin family that are both similar and dissimilar to HBD3 in terms of electrostatic potential. Synthesis and functional testing of a subset of these β-defensins showed that peptides with an HBD3-like electrostatic character bound to melanocortin receptors with high affinity, whereas those that were anticorrelated to HBD3 showed no binding affinity. These findings expand on the central role of electrostatics in the control of this ligand-receptor system and further demonstrate the utility of employing molecular-similarity analysis. Additionally, we identified several new potential ligands of melanocortin-1 receptor, which may have implications for our understanding of the role defensins play in melanocortin physiology.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Santa Cruz, Santa Cruz, California.
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Nix
authors.affiliation: HudsonAlpha Institute for Biotechnology, Huntsville, Alabama; Department of Genetics, Stanford University, Stanford, California.
authors.forename: Christopher B
authors.initials: CB
authors.lastname: Kaelin
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Santa Cruz, Santa Cruz, California.
authors.forename: Rafael
authors.initials: R
authors.lastname: Palomino
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Santa Cruz, Santa Cruz, California.
authors.forename: Jillian L
authors.initials: JL
authors.lastname: Miller
authors.affiliation: HudsonAlpha Institute for Biotechnology, Huntsville, Alabama; Department of Genetics, Stanford University, Stanford, California. Electronic address: gbarsh@hudsonalpha.org.
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Barsh
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Santa Cruz, Santa Cruz, California. Electronic address: glennm@ucsc.edu.
authors.forename: Glenn L
authors.initials: GL
authors.lastname: Millhauser
mesh_terms: D000595:Amino Acid Sequence; D001667:Binding, Competitive; D030562:Databases, Protein; D006801:Humans; D008956:Models, Chemical; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry; D011485:Protein Binding; D017510:Protein Folding; D044102:Receptor, Melanocortin, Type 1 / Q000737:chemistry*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity; D023083:beta-Defensins / Q000737:chemistry* / Q000235:genetics
chemical_list: C422950:DEFB103A protein, human; C106641:DEFB4A protein, human; D010455:Peptides; D044102:Receptor, Melanocortin, Type 1; D023083:beta-Defensins