4wha
From Proteopedia
Lipoxygenase-1 (soybean) L546A/L754A mutant
Structural highlights
Function[LOX1_SOYBN] Plant lipoxygenase may be involved in a number of diverse aspects of plant physiology including growth and development, pest resistance, and senescence or responses to wounding. With linoleate as substrate, L-1 shows a preference for carbon 13 as the site for hydroperoxidation (in contrast to L-2 and L-3, which utilize either carbon 9 or 13). At pH above 8.5, only (9Z,11E,13S)-13-hydroperoxyoctadeca-9,11-dienoate is produced, but as the pH decreases, the proportion of (9S)-hydroperoxide increases linearly until at pH 6.0 it represents about 25 % of the products.[1] Publication Abstract from PubMedThe enzyme soybean lipoxygenase (SLO) has served as a prototype for hydrogen-tunneling reactions, as a result of its unusual kinetic isotope effects (KIEs) and their temperature dependencies. Using a synergy of kinetic, structural, and theoretical studies, we show how the interplay between donor-acceptor distance and active-site flexibility leads to catalytic behavior previously predicted by quantum tunneling theory. Modification of the size of two hydrophobic residues by site-specific mutagenesis in SLO reduces the reaction rate 10(4)-fold and is accompanied by an enormous and unprecedented room-temperature KIE. Fitting of the kinetic data to a non-adiabatic model implicates an expansion of the active site that cannot be compensated by donor-acceptor distance sampling. A 1.7 A resolution X-ray structure of the double mutant further indicates an unaltered backbone conformation, almost identical side-chain conformations, and a significantly enlarged active-site cavity. These findings show the compelling property of room-temperature hydrogen tunneling within a biological context and demonstrate the very high sensitivity of such tunneling to barrier width. Extremely elevated room-temperature kinetic isotope effects quantify the critical role of barrier width in enzymatic C-H activation.,Hu S, Sharma SC, Scouras AD, Soudackov AV, Carr CA, Hammes-Schiffer S, Alber T, Klinman JP J Am Chem Soc. 2014 Jun 11;136(23):8157-60. doi: 10.1021/ja502726s. Epub 2014 Jun, 2. PMID:24884374[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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