Approaches to determine protein structural features from protein sequence include molecular mechanics and motif recognition. Here one correlates a Shannon information entropy defined as sequence entropy with respect to the flexibility of native globular proteins as described by inverse packing density. For individual proteins and the accompanying aggregate set a strong linear correlation is observed between the calculated sequence entropy and the corresponding flexibility determined at an associated residue position. Three different hydrophobicity scales were applied to the set of query proteins, and all three sets of query hydrophobicity values share similarity with the corresponding sequence entropy values. There appears strong correlation among sequence variability, relative hydrophobicity, and structural flexibility.