Structural characterization of two synthetic catalysts based on adipocyte lipid-binding protein.

Adipocyte lipid-binding protein (ALBP) is a small (14.5 kDa) 10-stranded beta-barrel protein found in mammalian fat cells. The crystal structures of various holo-forms of ALBP have been solved and show the fatty acid ligand bound in a large (approximately 400 A3) cavity isolated from bulk solvent. Examination of the cavity suggests that it would be a good site for the creation of an artificial catalyst, as numerous well defined crystal structures of ALBP are available and past studies have shown the conformation to be reasonably tolerant to modification and mutagenesis. Previous work has shown ALBP to be a good protein scaffold for exploring enantio- and stereoselective reactions; two constructs, ALBP attached to either a pyridoxamine or a phenanthroline group at C117, have been chemically characterized. Both modified proteins have been crystallized and their structures solved and refined. The X-ray models have been used to examine the origin of the chiral selectivity seen in the products. It is apparent that these covalent adducts reduce the internal cavity volume, sterically limiting substrate interactions with the reactive groups, as well as solvent access to potential intermediates in the reaction pathway.