48 CHAPTER 3 Forces at the Nanoscale order of 50% of the total, for a folded globular protein of moderate size) of apolar residues remains on the folded protein surface. The presence of an apolar residue in the vicinity of a hydrogen bond is a highly effective way of desolvating it. Folding success actually involves the juxtaposition of appropriate apolar residues with backbone hydrogen bonds. The effectiveness of desolvation of a hydrogen bond can be computed by simply counting the number ° of apolar residues within a sphere of about 7 A radius centered midway between the hydrogen bond donor and the hydrogen bond acceptor [54]. This approach, which can be carried out automatically using the atomic coordinates in the protein data bank (PDB), reveals the presence of dehydrons, underdesolvated (or "underwrapped") hydrogen bonds. Clusters of dehydrons are especially effective "sticky patches" on proteins. 3.5 WEAK COMPETING INTERACTIONS In any assembly process starting from a random arrangement, it is very likely that some of the initial connexions between the objects being assembled are merely oppor- tunistic and at a certain later stage will need to be broken in order to allow the overall