Minireview: The compact phase in polymers and proteins

Proteins are linear molecules. However, the simple model of a polymer viewed as spheres tethered together does not account for many of the observed characteristics of protein structures. Here we review some recent works tackling this problem. In particular, we will show that there is a growing evidence suggesting that the compact structures of folded proteins are selected in their gross topological features based on geometry and symmetry rather than on sequence consideration. They are poised at the edge of compaction, thus accounting for their flexibility. Different aspects of protein behavior can be rationalized by studying how the energy landscape of a single chain in the marginally compact phase can be modified.