Hydrophobic cluster propensities for the three secondary structures (α,β and coil) and for «multiple» clusters (clusters associated with at least two different regular secondary structures). Hydrophobic cluster species are classified in the decreasing order of their occurrences from the first to the third panels. Propensities are only reported for the chosen High Redundancy (HR) database (90 %, at the exception of a few hydrophobic clusters for which lower levels of redundancy were chosen – Additional file 3). Similar propensities were observed in the 25% database, when the occurrence of clusters within the considered species is yet sufficient to allow accurate statistics. Several cluster species are highlighted with arrows, with respect to their noticeable propensities for strand, helix or coil structures.