Enzyme structure and dynamics affect hydrogen tunneling: The impact of a remote side chain (I553) in soybean lipoxygenase-1

*Departments of Chemistry and of Molecular and Cell Biology, University of California, Berkeley, CA 94720-1460; and
^§Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX 75390

Contributed by Judith P. Klinman, November 28, 2007 (received for review September 20, 2007)

Abstract

This study examines the impact of a series of mutations at position 553 on the kinetic and structural properties of soybean lipoxygenase-1 (SLO-1). The previously uncharacterized mutants reported herein are I553L, I553V, and I553G. High-resolution x-ray studies of these mutants, together with the earlier studied I553A, show almost no structural change in relation to the WT-enzyme. By contrast, a progression in kinetic behavior occurs in which the decrease in the size of the side chain at position 553 leads to an increased importance of donor–acceptor distance sampling in the course of the hydrogen transfer process. These dynamical changes in behavior are interpreted in the context of two general classes of protein motions, preorganization and reorganization, with the latter including the distance sampling modes [Klinman JP (2006) Philos Trans R Soc London Ser B 361:1323–1331; Nagel Z, Klinman JP (2006) Chem Rev 106:3095–3118]. The aggregate data for SLO-1 show how judicious placement of hydrophobic side chains can influence enzyme catalysis via enhanced donor–acceptor hydrogenic wave function overlap.

Footnotes

^¶To whom correspondence should be addressed. E-mail: klinman{at}berkeley.edu
Author contributions: M.P.M. and J.P.K. designed research; M.P.M. and D.R.T. performed research; and M.P.M., D.R.T., and J.P.K. wrote the paper.
↵ ^†Present address: School of Natural Sciences, University of California, Merced, CA 95344.
The authors declare no conflict of interest.
This article contains supporting information online at www.pnas.org/cgi/content/full/0710643105/DC1.
Freely available online through the PNAS open access option.