Enzyme catalysis has been studied for over a century. How it actually occurs was not visualized until recently. By combining in crystallo catalysis with X-ray diffraction analysis of reaction intermediates, we have observed the intermediates of DNA synthesis and RNA degradation at unprecedented atomic details. Contrary to the canonical view that enzyme-substrate, transition state, and enzyme-product states have identical atomic composition and catalysis occurs by a two-Mg2+-ion mechanism with rearranging of electrons, protons and electrostatic charges, we have discovered that it is essential for enzyme-substrate complexes to capture a third Mg2+ and even K+ ions en route to product formation. Experimental data indicate that binding of the third Mg2+ ion is rate limiting in DNA synthesis and RNA degradation. We suspect that the free energy associated with metal-ion binding may overcome the barrier to new bond formation as well as old bond breakage.
Dr. Wei Yang is a Distinguished Investigator at the U.S. National Institutes of Health, where she has been since 1995. She was born in Shanghai, China and is a naturalized US citizen. She began her undergraduate studies of biochemistry at Fudan University in Shanghai and transferred to and received B.A. degree at SUNY at Stony Brook. She received her Ph.D. from Columbia University and postdoctoral training at Yale University. She uses a combination of structural and biochemical methods to elucidate molecular mechanisms underpinning DNA replication, repair and recombination, particularly in ATP mediated and Mg2+ dependent molecular recognition and catalysis. She received the 2011 Dorothy Crowfoot Hodgkin award (sponsored by the Protein Society) and 2017 Mildred Cohn Award in Biological Chemistry (sponsored by ASBMB). She is also anelected member of the National Academy of Sciences and American Academy of Arts and Sciences.