Crystallization of monoacylated proteins: influence of acyl chain length

The crystallization of monoacylated proteins has been investigated using a model system. Acylated derivatives of bovine pancreatic ribonuclease A, differing in their acyl chain lengths (10 to 16 carbon atoms), have been prepared using reverse micelles as microreactors. With one fatty acid moiety per polypeptide chain, covalently attached to the NH2 terminus of the protein, all the modified proteins have similar enzymatic activity and hydrodynamic radius as the native protein. Only the caprylated derivative can give crystals which diffract to high resolution. The resolved structure indicates that: (i) the protein folding is not modified by the chemical modification, (ii) the capryl moiety is not buried within the molecule but available for external interactions. Dynamic light scattering experiments on concentrated solutions show that the protein-protein interactions are dependent on acyl chain length. Proteins with the longest attached chains (14 and 16 carbon atoms) tend to self-associate through acyl group interactions.