Chemotaxis is the process of sensing chemical gradients and navigating towards favourable conditions. Bacterial chemotaxis is mediated by arrays of trans-membrane chemoreceptor proteins. The most common class of chemoreceptors have periplasmic ligand-binding domains (LBDs) that detect extra-cellular chemical signs and transduce these signals to the downstream chemotaxis machinery. The repertoire of chemoreceptor proteins in a bacterium determines the range of environmental signals to which it can respond. Pseudomonas syringae pv. actinidiae (Psa) is a plant pathogen which causes bac-terial canker of kiwifruit (Actinidia sp.). Compared to many other bacteria, Psa has a large number of chemoreceptors encoded in its genome (43) and most of these remain uncharacterized. A previous study identified PscC as a potential chemoreceptor for L-proline and other amino acid ligands. Here, we have characterized the interaction of PscC-LBD with L-proline using a combination of isothermal titration calorimetry (ITC) and X-ray crystallography. ITC confirmed direct binding of L-proline to PscC-LBD with KD value of 5.0 mM. We determined the structure of PscC-LBD in complex with L-proline. Our structural analysis showed that PscC-LBD adopts similar double-CACHE fold to several other amino acid chemo-receptors. A comparison of the PscC-LDB to other dCACHE structures highlights residues in the binding cavity which contribute to its ligand specificity. (C) 2021 The Authors. Published by Elsevier Inc.