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 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.
Kovalevsky
Andrey Y
AY
M888, Bioscience Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
Katz
Amy K
AK
Carrell
H L
HL
Hanson
Leif
L
Mustyakimov
Marat
M
Fisher
S Zoe
SZ
Coates
Leighton
L
Schoenborn
Benno P
BP
Bunick
Gerard J
GJ
Glusker
Jenny P
JP
Langan
Paul
P
D019747:Aldose-Ketose Isomerases / Q000737:chemistry* / Q000378:metabolism; D002384:Catalysis; D006859:Hydrogen / Q000737:chemistry*; D015394:Molecular Structure; D009502:Neutrons; D011485:Protein Binding; D014996:Xylulose / Q000737:chemistry* / Q000378:metabolism
D014996:Xylulose; D006859:Hydrogen; D019747:Aldose-Ketose Isomerases; C023298:xylose isomerase