When considering the first five PCs, the model explains about 75% of the variance observed in Fig. 2, indicating that these parameters are enough to explain practically all the variance of the model. However, the two first PCs better characterize the relationship between the physicochemical/biophysical properties and the groupings observed in Fig. 2. The third PC (correlated with number of disulfide bonds) does not add any new information in relation to the two first PCs. However, the fourth PC discriminates the groups as a function of GRAVY and percentage of alpha helix (data not

shown). To better understand the correlation between variables and objects described in Fig. 1 and Fig. 2, the same data were also shown in Fig. 3 and Fig. 4, emphasizing the three dimensional representations of the correlations between the samples and the variables: aliphaticity (Fig. 3A), GRAVY (Fig. 3B), net charge (Fig. 3C), alpha helix (%) (Fig. 4A), ABT-199 manufacturer and Boman index (Fig. 4B). Fig. 5 shows the residual variance of the model used in the present study; it shows a step-like representation of the calibration

variance and the validation variance for different numbers of PCs. There is a tendency for these values to decrease as a function of the increase in the number of PCs, indicating that the present model is valid, because a higher number of PCs gives a smaller error in the model. In fact, the calibration variance Dasatinib ic50 and the validation variance tend to zero after a few PCs. The purpose of multivariate calibration is to construct a predictive model based on multiple predictor variables. Multivariate calibration is in fact a two-stage procedure: (i) the model is build using training P-type ATPase samples, for which the predictor and predictand variables are known or measured, and (ii) the model is then validated by comparing the predictions against reference values for samples that were not used for the model building [36]. To validate the model used to predict the activities of Hymenoptera venom peptides, another series of 80 peptides from other

organisms (Table S2 in supplementary information) presenting the same types of activities as those presented by the Hymenoptera peptides were analyzed and compared against the Hymenoptera model. After the calculation of predictor and predictand variables for these peptides, their distribution in the PCA score plot (Fig. 6) and PCA X-loadings plot (Fig. 7) gave a very similar pattern as that observed for the Hymenoptera peptides (Fig. 2). In both cases, the grouping pattern was the same; i.e., those peptides described in the literature as mast cell degranulators were distributed within the same coordinates already occupied by the mastoparans, while a similar distribution was also observed for the other groups (chemotactic peptides, kinins, tachykinins, linear antibiotic peptides and the group of peptides presenting disulfide bridges).