An Alternate Mechanism for the Methylation of Phosphoethanolamine Catalyzed by Plasmodium falciparum Phosphoethanolamine Methyltransferase [Protein Structure and Folding]

October 6th, 2014 by Saen-oon, S., Lee, S. G., Jez, J. M., Guallar, V.

The phosphobase methylation pathway catalyzed by the phosphoethanolamine methyltransferase in Plasmodium falciparum (PfPMT), the malaria parasite, offers an attractive target for anti-parasitic drug development. PfPMT methylates phosphoethanolamine (pEA) to phosphocholine (pCho) for use in membrane biogenesis. Quantum mechanics and molecular mechanics (QM/MM) calculations tested the proposed reaction mechanism for methylation of pEA involving the previously identified Tyr19-His132 dyad, which indicated an energetically unfavorable mechanism. Instead, the QM/MM calculations suggested an alternate mechanism involving Asp128. The reaction coordinate involves the step-wise transfer of a proton to Asp128 via a bridging water molecule followed by a typical SN2-type methyl transfer from S-adenosylmethionine to pEA. Functional analysis of the D128A, D128N, D128Q, and D128N PfPMT mutants show a loss of activity with pEA, but not with the final substrate of the methylation pathway. X-ray crystal structures of the PfPMT-D128A mutant in complex with S-adenosylhomocysteine and either pEA or pCho reveal how mutation of Asp128 disrupts a hydrogen bond network in the active site. The combined QM/MM, biochemical, and structural studies identify a key role for Asp128 in the initial step of the phosphobase methylation pathway in Plasmodium and provide molecular insight on the evolution of multiple activities in the active site of the PMT.
  • Posted in Journal of Biological Chemistry, Publications
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