title: Computational survey of peptides derived from disulphide-bonded protein loops that may serve as mediators of protein-protein interactions.
abstract: BACKGROUND
  Bioactive cyclic peptides derived from natural sources are well studied, particularly those derived from non-ribosomal synthetases in fungi or bacteria. Ribosomally synthesised bioactive disulphide-bonded loops represent a large, naturally enriched library of potential bioactive compounds, worthy of systematic investigation.
  
  
  RESULTS
  We examined the distribution of short cyclic loops on the surface of a large number of proteins, especially membrane or extracellular proteins. Available three-dimensional structures highlighted a number of disulphide-bonded loops responsible for the majority of the likely binding interactions in a variety of protein complexes, due to their location at protein-protein interfaces. We find that disulphide-bonded loops at protein-protein interfaces may, but do not necessarily, show biological activity independent of their parent protein. Examining the conservation of short disulphide bonded loops in proteins, we find a small but significant increase in conservation inside these loops compared to surrounding residues. We identify a subset of these loops that exhibit a high relative conservation, particularly among peptide hormones.
  
  
  CONCLUSIONS
  We conclude that short disulphide-bonded loops are found in a wide variety of biological interactions. They may retain biological activity outside their parent proteins. Such structurally independent peptides may be useful as biologically active templates for the development of novel modulators of protein-protein interactions.
authors.forename: Fergal J
authors.initials: FJ
authors.lastname: Duffy
authors.forename: Marc
authors.initials: M
authors.lastname: Devocelle
authors.forename: David R
authors.initials: DR
authors.lastname: Croucher
authors.affiliation: School of Medicine and Medical Science, University College Dublin, Belfield, Dublin 4, Ireland. denis.shields@ucd.ie.
authors.forename: Denis C
authors.initials: DC
authors.lastname: Shields
mesh_terms: D019295:Computational Biology / Q000379:methods*; D017124:Conserved Sequence; D004220:Disulfides / Q000737:chemistry*; D005110:Extracellular Space / Q000378:metabolism; D006801:Humans; D010456:Peptides, Cyclic / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D011506:Proteins / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D004220:Disulfides; D010456:Peptides, Cyclic; D011506:Proteins