Ligand binding surface complementarity

Several hydrophilic residues project into the /3 barrel and form a network of hydrogen bonds and salt links, clustered around the carboxylate groups of the ligand. At the current crystallographic resolution, the network has been restricted to include only five water molecules, all of which are in the barrel. Other side chains create a hydrophobic environment around the fatty acid tail. The complementarity of ligand and protein appears relatively poor and the fatty acid still has an accessible surface area of 33 A. This may be related to the lack of specificity for ligand that has been reported by Uyemura et al. (1984) they report that oleic acid, retinoic acid, and retinol are able to bind to P2. 

Electrostatic complementarity between the enzyme and its ligand is illustrated on the example of the binding of the Lys-15 side chain of bovine pancreatic trypsin inhibitor (BPTI) to the specificity pocket of trypsin (Figure 4.). The MEP of BPTI which is displayed on the van der Waals envelope of the Lys side chain is complementary to that displayed on the same surface but emerging from the enzyme... 

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