Interatomic Distances Chi-Squared Test

Models in silico were developed using Molecular Modelling Pro Plus, version 6.22, and ChemSite, version 5.10, produced by ChemSW (Accelrys Inc., San Diego, USA), as described in Methods. For EPL001’s 9KEFNNI14, nine atoms were selected from side chains and two from the peptide backbone, thus: a = nitrogen in the side-chain of K9; b = delta carbon in E; c = hydroxyl oxygen in the side-chain of E; d = beta carbon in F; e = gamma carbon of F; f = peptide bond carbon of I; g = delta carbon of I; h = gamma carbon of N13; i = nitrogen of the side-chain of N13; j = peptide bond carbon of N12, k = nitrogen of side-chain of N12. This permitted 46 measurements, each atom to every other atom: a-b, a-c etc. Distances between the same atoms were calculated for KEFNNI as a free peptide, with comparisons reducing in number for free EFNNI through free FNNI to free NNI. The peptide MKPVFNNI has also been modelled. A chi-squared test was used, with measurements from the EPL001 model in silico representing Expected (E) and measurements from the modelled free peptides as Observed (O). Chi-squared values were calculated on the basis of (O-E)2/E. dof = degrees of freedom.