Figure 2. Global Degree Correlation Suggest Bias against Hub–Hub Interactions.

Proteins in either a combined HTP dataset (A) or the full HC dataset (B) were binned logarithmically by connectivity (with two bins per decade), and interactions among nodes in each of these bins were computed. The ratios of observed over the expected number of interactions are shown; the x- and y-axes both represent connectivity. Degree correlation profiles were computed as described in the Methods section; expected values were computed by generating 50 random networks generated via edge-swapping procedure as described [16]. All colored regions are statistically significant (standard deviation greater than or equal to ±3, representing p < 0.01), with enrichment highlighted in blue and depletion in red; ratios colored in white do not deviate significantly from unity. Areas bounded by rectangles represent interaction space between hubs, defined as the degree threshold exceeded by 10% of the hubs. This threshold was 18 for HTP and 21 for HC.