THE CRYSTAL STRUCTURE OF MALIC ENZYME FROM AYWB PHYTOPLASMA REVEALS A NOVEL DIMERIC CONFORMATION

ALVAREZ C.; TRAJTENBERG F; LARRIEUX N.; SAIGO M.; MUSSI MA; ANDREO C.; DRINCOVICH M.F.; BUSCHIAZZO A.

Santiago del Estero

Congreso; XI Reunión Anual de la Asociación Argentina de Cristalografía (AACr); 2015

Phytoplasmas are wall-less phytopathogenic bacteria that produce devastating effects on a wide variety of plants. Phytoplasmas genomes have lost many metabolic genes as a result of reductive evolution, and the glycolytic pathway is not functional. Due to the high concentration of C4 compounds in plants and a malic enzyme (ME) encoded in all sequenced phytoplasmas genomes, it is highly possible that C4 acids are used by these bacteria. Considering this, we have performed a detailed characterization of the Candidatus Phytoplasma AYWB ME (AYWB-ME). All the results obtained indicate that this enzyme is involved in energy generation, which is specially suggested by its tight modulation by adenine nucleotides. The differential properties of this enzyme, in combination with the fact that AYWB-ME is one of the smallest among all MEs characterized, made us wonder how this small protein has retained the enzymatic activity and gained its particular modulation. To answer this issue, we have recently obtained the first structure of a phytoplasma ME in the presence of NAD and MgCl2 (5CEE pdb code), which diffracted at 2.6 Å resolution using an in-house source. The diffraction pattern analysis shows that these crystals present a P3121 space group with a twinning phenomenon (-h,-k,l). The processing was performed with Mosflm/Scala programs and the initial phasing by molecular replacement using Phaser. After density modification, the atomic models were built in the maps using Coot program and iteratively refined with Phenix. The structure shows a dimer conformation based on a scaffold with unique characteristics. Among these, it is observed that the active site of each monomer is complemented by essential residues (e.g. Tyr 36) from the other monomer. The structure indicate a novel strategy for a ME in order to build its active sites, making this enzyme an interesting starting point to make a rational genetic design of ME.