An Alternative Mechanism for the Methylation of Phosphoethanolamine Catalyzed by Plasmodium falciparum Phosphoethanolamine Methyltransferase*

Abstract

Background:In Plasmodium, phosphoethanolamine methyltransferase (PfPMT) is essential for normal growth and development. Results: Computational, biochemical, and structural studies suggest catalytic and structural roles for Asp-128 in PfPMT. Conclusion: Asp-128 is critical for specific methylation of phosphoethanolamine and not other phosphobases. Significance: This work provides new insight on the evolution of multiple substrate activity in PMT from different organisms.

Structural and Functional Studies of Pavine N-Methyltransferase from Thalictrum flavum Reveal Novel Insights into Substrate Recognition and Catalytic Mechanism

“…Clearly, additional work is required to define more specific functions in catalysis, which may differ depending on the specific substrate. It is notable that these two residues are found in a loop that is similar to that seen in PfPMT, where Asp 128 was recently proposed to assist with general base catalysis (14). The moderate levels of sequence conservation seen for several other residues in the 70s loop and ␣4 of PavNMT suggest that other positions may also be of functional importance for the NMTs involved with BIA biosynthesis.…”

“…Mutagenesis studies have also implicated His 132 and Tyr 19 in PfPMT for a possible role in catalysis, but quantum mechanics/ molecular modeling calculations do not support a role in base catalysis as initially proposed (8,14). Recent work examining changes in the kinetic and binding isotope effects of mutations to the Tyr 21 residue of glycine N-methyltransferase (GNMT) suggests that the bulky aromatic side chain of the tyrosine residue may play a role in activating the donor methyl group in SAM (16).…”

“…Recent studies of PfPMT from P. falciparum proposed that Tyr 19 , His 132 , Asp 128 , and a bound water molecule combine to provide general base catalysis and electrostatic positioning effects to increase the reactivity of the amino group of the methyl acceptor phosphoethanolamine (8,14). Asp 128 appears to be particularly important for the primary amine substrate but does not appear to play the same role for secondary or tertiary amine substrates.…”

“…Asp 128 appears to be particularly important for the primary amine substrate but does not appear to play the same role for secondary or tertiary amine substrates. For the primary amine substrate in PfPMT, quantum mechanics and molecular modeling calculations suggest that Asp 128 probably accepts a proton from a bridging water molecule that in turn activates the amino group through base catalysis (14).…”

Conformational changes in the di-domain structure of Arabidopsis phosphoethanolamine methyltransferase leads to active-site formation

“…8). Structural and biochemical analysis of the P. falciparum PMT indicates that its active site contains substitutions to allow for methylation of pEA and that these residue changes are not found in the MT2 domains of the plant and nematode enzymes (15)(16)(17)(18). It appears that the loss of the MT1 domain and alteration of the MT2 domain active site led to a multifunctional single domain PMT of the apicomplexans (12,19).…”