Characterization and 1.57 Å resolution structure of the key fire blight phosphatase AmsI fromErwinia amylovora

What is it about?

AmsI is a low-molecular-weight protein tyrosine phosphatase that regulates the production of amylovoran in the Gram-negative bacterium Erwinia amylovora, a specific pathogen of rosaceous plants such as apple, pear and quince. Amylovoran is an exopolysaccharide that is necessary for successful infection. In order to shed light on AmsI, its structure was solved at 1.57 A ˚ resolution at the same pH as its highest measured activity (pH 5.5). In the active site, a water molecule, bridging between the catalytic Arg15 and the reaction-product analogue sulfate, might be representative of the water molecule attacking the phospho-cysteine intermediate in the second step of the reaction mechanism.

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Why is it important?

Fire blight is a devastating disease affecting rosaceous plants such as apple, pear and quince (Vanneste, 2000). The Gramnegative bacterium Erwinia amylovora is the aetiological agent of the disease. Currently, the main methods to control fire blight are the use of biological and chemical pesticides, antibiotics and resistant cultivars obtained through classical breeding or genetic engineering. Infected cultivars commonly require quarantine, pruning and/or eradication of the plants (Gusberti et al., 2015). Within the E. amylovora genome, the ams operon is necessary for pathogenicity and is responsible for the synthesis of amylovoran (Bugert & Geider, 1995), which is a complex branched heteropolysaccharide that is essential for virulence and pathogenicity, and is the major component of the exopolysaccharide (EPS) capsule of the bacterium together with levan (Caputi, Cianci et al., 2013; Caputi, Nepogodiev et al., 2013; Geier & Geider, 1993; Nimtz et al., 1996; Bernhard et al., 1993; Wuerges et al., 2015). The AmsI protein, encoded by the amsI gene, is a cytoplasmatic key enzyme of amylovoran metabolism, and thus a potential drug target for the control of fire blight.