Small molecule crystallography: insight into biological activity
J.P. Glusker · Acta Crystallographica Section A Foundations of Crystallography · 1987
Throughout biological history, until this decade, proteins have evolved by evolution and natural selection.For the first time, proteins can now be created or modified at will, limited only by our own powers of understanding.Most of the understanding of protein structure has come from protein crystallography.Protein engineering provides a means to extend and deepen understanding of protein structure, protein folding and protein function.The catalytic function of an enzyme is a particularly sensmve property, because enzyme kinetic parameters can be interpreted in terms of free energy changes during the catalytic process.A change in these parameters, caused by engineering a single amino-acid change, gives a direct measure of a change in the free••• energy of interaction atsome point in the catalytic process.'Calorimetry' of individual hydrogen bonds and other specific interactions is possible.Larger changes, involving whole sections of chain or domains, can also be studied; similarly the energy of quaternary interaction between protein monomers can be changed.These interpretations rely on assumptions about the structure of the factitious mutant which can be checked crystallographically.Many small changes produce molecules which crystallise isomorphously with the wild -type enzyme.More radical changes will result in altered crystal structures which can be solved by molecular replacement techniques.Protein engineering can be used to assist crystallography, by the elimination of a mobile domain or a site of glycosylation to produce better crystals, or by introduction of specific amino acids to provide sites for heavy atoms.Work on tyrosyl-tRNA synthetase (with A.R.Fersht and G. Winter) is used to illustrate these points.Some of the possible useful applications of protein engineering are discussed.