Interatomic Distances Chi-Squared Test

Models <i>in silico</i> 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 <i>Methods</i>. 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.