Substrate-assisted catalysis: Molecular basis and biological significance

Substrate-assisted catalysis (SAC) is the process by which a functional gro up in a substrate contributes to catalysis by an enzyme. SAC has been demon strated for representatives of three major enzyme classes: serine proteases , GTPases, and type II restriction endonucleases, as well as lysozyme and h exose-1-phosphate uridylyltransferase. Moreover, structure-based prediction s of SAC have been made for many additional enzymes. Examples of SAC includ e both naturally occurring enzymes such as type II restriction endonuclease s as well as engineered enzymes including serine proteases. Ln the latter c ase, a functional group from a substrate can substitute for a catalytic res idue replaced by site-directed mutagenesis. From a protein engineering pers pective, SAC provides a strategy for drastically changing enzyme substrate specificity or even the reaction catalyzed. From a biological viewpoint, SA C contributes significantly to the activity of some enzymes and may represe nt a functional intermediate in the evolution of catalysis. This review foc uses on advances in engineering enzyme specificity and activity by SAG, tog ether with the biological significance of this phenomenon.