Hydrogen Location in Stages of an Enzyme-Catalyzed Reaction: Time-of-Flight Neutron Structure of d-Xylose Isomerase with Bound d-Xylulose

The time-of-flight neutron Laue technique has been used to determine the location of hydrogen atoms in the enzyme d-xylose isomerase (XI). The neutron structure of crystalline XI with bound product, d-xylulose, shows, unexpectedly, that O5 of d-xylulose is not protonated but is hydrogen-bonded to do...

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Published in:Biochemistry (Easton) 2008-07, Vol.47 (29), p.7595-7597
Main Authors: Kovalevsky, Andrey Y, Katz, Amy K, Carrell, H. L, Hanson, Leif, Mustyakimov, Marat, Fisher, S. Zoe, Coates, Leighton, Schoenborn, Benno P, Bunick, Gerard J, Glusker, Jenny P, Langan, Paul
Format: Article
Language:English
Subjects:
Aldose-Ketose Isomerases - chemistry
Aldose-Ketose Isomerases - metabolism
Catalysis
Hydrogen - chemistry
Molecular Structure
Neutrons
Protein Binding
Xylulose - chemistry
Xylulose - metabolism
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Summary:The time-of-flight neutron Laue technique has been used to determine the location of hydrogen atoms in the enzyme d-xylose isomerase (XI). The neutron structure of crystalline XI with bound product, d-xylulose, shows, unexpectedly, that O5 of d-xylulose is not protonated but is hydrogen-bonded to doubly protonated His54. Also, Lys289, which is neutral in native XI, is protonated (positively charged), while the catalytic water in native XI has become activated to a hydroxyl anion which is in the proximity of C1 and C2, the molecular site of isomerization of xylose. These findings impact our understanding of the reaction mechanism.
ISSN:0006-2960
1520-4995
DOI:10.1021/bi8005434