The crystal structure of the malic enzyme from Candidatus Phytoplasma reveals the minimal structural determinants for a malic enzyme

ALVAREZ, C. E.; TRAJTENBERG, F.; LARRIEUX, N.; SAIGO, M.; GOLIC, A.; ANDREO, C. S.; HOGENHOUT, S. A.; MUSSI, M. A.; DRINCOVICH, M. F.; BUSCHIAZZO, A.

Acta Crystallographica Section D Structural Biology

International Union of Crystallography

Año: 2018 vol. 74 p. 332 - 340

2059-7983

Phytoplasmas are wall-less phytopathogenic bacteria that produce devastatingeffects in a wide variety of plants. Reductive evolution has shaped their genome, with the loss of many genes, limiting their metabolic capacities. Owing to the high concentration of C4 compounds in plants, and the presence of malic enzyme (ME) in all phytoplasma genomes so far sequenced, the oxidative decarboxylation of l-malate might represent an adaptation to generate energy. Aster yellows witches?-broom (Candidatus Phytoplasma) ME (AYWB-ME) is one ofthe smallest of all characterized MEs, yet retains full enzymatic activity. Here, the crystal structure of AYWB-ME is reported, revealing a unique fold thatdiffers from those of ?canonical? MEs. AYWB-ME is organized as a dimericspecies formed by intertwining of the N-terminal domains of the protomers. As aconsequence of such structural differences, key catalytic residues such as Tyr36are positioned in the active site of each protomer but are provided by the otherprotomer of the dimer. A Tyr36Ala mutation abolishes the catalytic activity,indicating the key importance of this residue in the catalytic process but not in the dimeric assembly. Phylogenetic analyses suggest that larger MEs (large subunit or chimeric MEs) might have evolved from this type of smaller scaffoldby gaining small sequence cassettes or an entire functional domain. The Candidatus Phytoplasma AYWB-ME structure showcases a novel minimal structure design comprising a fully functional active site, making this enzyme anattractive starting point for rational genetic design