jp4049814_si_001.xyz (7.38 kB)
Hydrolysis of the E2P Phosphoenzyme of the Ca2+-ATPase: A Theoretical Study
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posted on 2013-08-08, 00:00 authored by Maria E. Rudbeck, Margareta R. A. Blomberg, Andreas BarthDephosphorylation of the E2P phosphoenzyme
intermediate of the
sarcoplasmic reticulum Ca2+-ATPase was studied using density
functional theory. The hydrolysis reaction proceeds via a nucleophilic
attack on the phosphorylated residue Asp351 by a water molecule, which
is positioned by the nearby residue Glu183 acting as a base. The activation
barrier was calculated to be 14.3 kcal/mol, which agrees well with
values of 15–17 kcal/mol derived from experimentally observed
rates. The optimized structure of the transition state reveals considerable
bond breakage between phosphorus and the Asp351 oxygen (distance 2.19 Å)
and little bond formation to the attacking water oxygen (distance
2.26 Å). Upon formation of the singly protonated phosphate product,
Glu183 becomes protonated. The bridging aspartyl phosphate oxygen
approaches Lys684 progressively when proceeding from the reactant
state (distance 1.94 Å) via the transition state (1.78 Å)
to the product state (1.58 Å). This stabilizes the negative charge
that develops on the leaving group. The reaction was calculated to
be slightly endergonic (+0.9 kcal/mol) and therefore reversible, in
line with experimental findings. It is catalyzed by a preorganized
active site with little movement of the nonreacting groups except
for a rotation of Thr625 toward the phosphate group.
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aspartyl phosphate oxygen approaches Lys 684hydrolysis reaction proceedsnucleophilic attackThr 625phosphorylated residue Asp 351optimized structureTheoretical StudyDephosphorylationbond formationtransition statereactant stateAsp 351 oxygenkcalwater oxygenactivation barrierE 2P Phosphoenzymesarcoplasmic reticulumprotonated phosphate productbond breakageGlu 183water moleculeresidue Glu 183nonreacting groupsE 2P phosphoenzymephosphate group
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