  A major issue in biology is the understanding of the interactions between
proteins. These interactions can be described by a network, where the proteins
are modeled by nodes and the interactions by edges. The origin of these protein
networks is not well understood yet. Here we present a two-step model, which
generates clusters with the same topological properties as networks for
protein-protein interactions, namely, the same degree distribution, cluster
size distribution, clustering coefficient and shortest path length. The
biological and model networks are not scale free but exhibit small world
features. The model allows the fitting of different biological systems by
tuning a single parameter.
