Kenneth J. Woycechowsky, Department of Chemistry, University of Utah, 315 South 1400 East, Room 2020, Salt Lake City, UT 84112
Natural enzymes possess highly ordered native states that nevertheless undergo changes in conformation and dynamics during catalysis. Surprisingly, a laboratory evolved chorismate mutase (mMjCM) retains high catalytic efficiency despite lacking a well-ordered native state. This molten globular enzyme occupies a rapidly interconverting ensemble of structures that fluctuate around a loosely packed hydrophobic core, and a dramatic ordering transition occurs upon binding to catalytically relevant ligands. Using site-specifically isotope labeled protein in combination with NMR spectroscopy, we charaqcterized the molten globule state of mMjCM as well as its more ordered complexes with product and a transition state analog. The ordering transition seen upon ligand binding leads to dramatic dampening of the enormous millisecond timescale protein motions seen for the free enzyme. Further, the product complex shows greater dynamics than the TSA complex, indicating that mMjCM becomes progressively more ordered as it proceeds from the free enzyme to the ground state complex and onwards toward the transition state. Comparison with the thermostable parent of mMjCM reveals that the extent of ordering upon approach to the transition state does not correlate with the extent of transition state stabilization in this system. While mMjCM displays a great deal of dynamic behavior, dynamics do not seem to drive catalysis.
