title: Search for allosteric disulfide bonds in NMR structures.
abstract: BACKGROUND
  Allosteric disulfide bonds regulate protein function when they break and/or form. They typically have a -RHStaple configuration, which is defined by the sign of the five chi angles that make up the disulfide bond.
  
  
  RESULTS
  All disulfides in NMR and X-ray protein structures as well as in refined structure datasets were compared and contrasted for configuration and strain energy.
  
  
  CONCLUSIONS
  The mean dihedral strain energy of 55,005 NMR structure disulfides was twice that of 42,690 X-ray structure disulfides. Moreover, the energies of all twenty types of disulfide bond was higher in NMR structures than X-ray structures, where there was an exponential decrease in the mean strain energy as the incidence of the disulfide type increased. Evaluation of protein structures for which there are X-ray and NMR models shows that the same disulfide bond can exist in different configurations in different models. A disulfide bond configuration that is rare in X-ray structures is the -LHStaple. In NMR structures, this disulfide is characterised by a particularly high potential energy and very short alpha-carbon distance. The HIV envelope glycoprotein gp120, for example, is regulated by thiol/disulfide exchange and contains allosteric -RHStaple bonds that can exist in the -LHStaple configuration. It is an open question which form of the disulfide is the functional configuration.
authors.affiliation: UNSW Cancer Research Centre, University of New South Wales, Sydney, NSW, Australia. b.schmidt@unsw.edu.au <b.schmidt@unsw.edu.au>
authors.forename: Bryan
authors.initials: B
authors.lastname: Schmidt
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Hogg
mesh_terms: D000495:Allosteric Site; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D004220:Disulfides / Q000737:chemistry*; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D011487:Protein Conformation; D011506:Proteins / Q000737:chemistry*
chemical_list: D004220:Disulfides; D011506:Proteins