  The three dimensional structure of a protein is an outcome of the
interactions of its constituent amino acids in 3D space. Considering the amino
acids as nodes and the interactions among them as edges we have constructed and
analyzed protein contact networks at different length scales, long and
short-range. While long and short-range interactions are determined by the
positions of amino acids in primary chain, the contact networks are constructed
based on the 3D spatial distances of amino acids. We have further divided these
networks into sub-networks of hydrophobic, hydrophilic and charged residues.
Our analysis reveals that a significantly higher percentage of assortative
sub-clusters of long-range hydrophobic networks helps a protein in
communicating the necessary information for protein folding in one hand; on the
other hand the higher values of clustering coefficients of hydrophobic
sub-clusters play a major role in slowing down the process so that necessary
local and global stability can be achieved through intra connectivities of the
amino acid residues. Further, higher degrees of hydrophobic long-range
interactions suggest their greater role in protein folding and stability. The
small-range all amino acids networks have signature of hierarchy. The present
analysis with other evidences suggest that in a protein's 3D conformational
space, the growth of connectivity is not evolved either through preferential
attachment or through random connections; rather, it follows a specific
structural necessity based guiding principle - where some of the interactions
are primary while the others, generated as a consequence of these primary
interactions are secondary.
