Exit Regions of Cavities in Proteins

Proteins have a complex three dimensional structure with empty cavities and tunnels in the inter-atomic space and these spatial features are often essential for the correct biological function. Many discrete and analytical methods have been developed for the computation, analysis and visualization of these features. In this paper, we focus on the connection of cavities with the space outside a protein. This connection would normally be described by tunnels. However, the number of possible solutions can be very high and therefore a nontrivial pruning of solutions is needed to deliver only a few representatives. Therefore, we propose an alternative kind of spatial features called exit regions of cavities. These regions capture the critical locations where a spherical probe, initially placed in a cavity, can leave the protein if the probe is allowed to shrink. The shape of an exit region is more detailed when compared against the simple circular profile of a tunnel. Tunnels, on the other hand, provide more information about the exact path.