CELL-TO-CELL VARIABILITY IN LIGAND-RECEPTOR BINDING DYNAMICS

VASEN G; BUSH A; COLMAN-LERNER A

Congreso; LI Reunión Anual Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2015

Biological systems are composed of physical constituents that constrain their performance leading to cell-to-cell variation, a feature often regulated by active mechanisms. Here we focus our attention on the cell-to-cell variability that arrises from the dynamics of ligand-receptor interaction. We characterized in single cells the binding of fluorescently-labeled sexual pheromone (alpha factor, αF*) to its G-coupled protein receptor, Ste2, in Saccharomyces cerevisiae. By using competition experiments with unlabeled pheromone (αF) and strains lacking the receptor, we confirmed the specificity of the fluorecent analog association with the cell surface. Performing binding experiments, we measured a dissociation constant for αF*-Ste2 (KD) of 23nM that ranges in the order of αF KD, 5nM. Using quantitative fluorescence microscopy and image segmentation analysis, we determined binding dynamics for each cell and on/off rates, KD and total number of receptors were calculated. We observed a broad distribution of both KD values and total number of Ste2 between cells with coefficient of variation of 0.46 and 0.35, respectively. Finally, we studied the effect of mutations in the receptor and cell metabolic state on the control of cell-to-cell binding variability. Taking these data, we found that ligand-receptor binding dynamics is a new, previously unexplored, source of cellular signaling noise.