In:
Acta Crystallographica Section D Structural Biology, International Union of Crystallography (IUCr), Vol. 74, No. 4 ( 2018-04-01), p. 332-340
Abstract:
Phytoplasmas are wall-less phytopathogenic bacteria that produce devastating effects 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 C 4 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 of the smallest of all characterized MEs, yet retains full enzymatic activity. Here, the crystal structure of AYWB-ME is reported, revealing a unique fold that differs from those of `canonical' MEs. AYWB-ME is organized as a dimeric species formed by intertwining of the N-terminal domains of the protomers. As a consequence of such structural differences, key catalytic residues such as Tyr36 are positioned in the active site of each protomer but are provided by the other protomer 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 scaffold by 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 an attractive starting point for rational genetic design.
Type of Medium:
Online Resource
ISSN:
2059-7983
DOI:
10.1107/S2059798318002759
DOI:
10.1107/S2059798318002759/gi5016sup1.pdf
Language:
Unknown
Publisher:
International Union of Crystallography (IUCr)
Publication Date:
2018
detail.hit.zdb_id:
2968623-4
Permalink