# Molecular Basis of Pseudomonas syringae pv actinidiae Levansucrase Inhibition by a Multivalent Iminosugar

## TL;DR

Scientists found a new inhibitor that can block a key enzyme in a plant pathogen, which could help control bacterial survival.

## Contribution

The discovery of a tetravalent pyrrolidine iminosugar as the first known levansucrase inhibitor with competitive inhibition behavior.

## Key findings

- TPIS inhibits levansucrase activity in multiple P. syringae genotypes with a micromolar inhibition constant.
- X-ray crystal structures confirm TPIS as a competitive inhibitor and reveal partial binding interactions.
- Multivalency is crucial for effective inhibition, as monovalent PIS has negligible effect.

## Abstract

Levansucrases are
a class of polysaccharide-processing enzymes
widely distributed among plant pathogenic bacteria, such as Pseudomonas syringae and Erwinia amylovora. Therefore, the modulation of levansucrase activity could represent
a new strategy to reduce the microbial survival of such bacteria.
Herein, we identified a tetravalent pyrrolidine iminosugar (TPIS)
as the first levansucrase inhibitor described to date. TPIS reversibly
inhibits sucrose hydrolysis and levan polymerization of levansucrase
derived from different bacterial genotypes of P. syringae, showing competitive behavior and an inhibition constant (K
i) in the micromolar range. Interestingly, the
monovalent pyrrolidine iminosugar (PIS) analogue shows negligible
inhibition, suggesting that multivalency plays a pivotal role in the
interaction with levansucrase. To gain insight into the binding mechanism,
the X-ray crystal structures of the beta levansucrase isoform from P. syringae pv actinidiae (Psa) in its native form and in complex with TPIS were solved, confirming
TPIS as a competitive inhibitor of levansucrases. Only a portion of
TPIS, corresponding to one chain of the tetravalent iminosugar derivative,
was visible in the electron density maps. Nevertheless, our structural
data provided an adequate comprehension of the inhibitor/enzyme interactions,
sufficient to exclude some of the possible inhibition mechanisms justifying
a multivalent effect and pave the way for the development of new,
more potent inhibitors.