Structural basis of calcium and galactose recognition by the lectin PA-IL of Pseudomonas aeruginosa

The structure of the tetrameric Pseudomonas aeruginosa lectin I (PA-IL) in complex with galactose and calcium was determined at 1.6 Angstrom resolution, and the native protein was solved at 2.4 Angstrom resolution. Each monomer adopts a beta-sandwich fold with ligand binding site at the apex. All galactose hydroxyl groups, except O1, are involved in a hydrogen bond network with the protein and O3 and O4 also participate in the coordination of the calcium ion. The stereochemistry of calcium galactose binding is reminiscent of that observed in some animal C-type lectins. The structure of the complex provides a framework for future design of anti-bacterial compounds. (C) 2003 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.