Effects of the Surface Densities of Glycoclusters on the Determination of Their IC50 and Kd Value Determination by Using a Microarray

Pseudomonas aeruginosa (PA) is an opportunistic bacterium involved in 10-30% of nosocomial diseases. It causes severe lung injury to cystic fibrosis patients, often leading to patient death. PA strains are multidrug resistant, thus making the design of new therapeutics a challenge for public health. One promising therapeutic option is to design glycoclusters that target the virulence factor of PA. LecA is a galactose-specific lectin that might be involved in adhesion and biofilm formation by PA. The DNA-directed immobilization (DDI) microarray is a powerful tool for screening and understanding of structure-activity relationships between glycoclusters and lectins. High-throughput and multiplexed analysis of lectin-glycocluster interactions on a DDI microarray allows measurement of IC50 and dissociation constant (K-d) values with minute amounts of material. In order to study the robustness of the DDI microarray in determination of IC50 and K-d values, the impact of glycocluster surface density was investigated. The data obtained show that measured IC50 values were influenced by glycocluster surface density: as the density of glycoclusters increases, the measured IC50 values increase too. In contrast, the measured K-d values were not affected by glycocluster surface density, provided that the experimental conditions allow interaction between glycocluster and lectin at single-molecule level (no surface cluster effect).