  Proteins are an important class of biomolecules that serve as essential
building blocks of the cells. Their three-dimensional structures are
responsible for their functions. In this thesis we have investigated the
protein structures using a network theoretical approach. While doing so we used
a coarse-grained method, viz., complex network analysis. We model protein
structures at two length scales as Protein Contact Networks (PCN) and as
Long-range Interaction Networks (LINs). We found that proteins by virtue of
being characterised by high amount of clustering, are small-world networks.
Apart from the small-world nature, we found that proteins have another general
property, viz., assortativity. This is an interesting and exceptional finding
as all other complex networks (except for social networks) are known to be
disassortative. Importantly, we could identify one of the major topological
determinant of assortativity by building appropriate controls.
