 G SPR measurements of SiaC (left) or SiaCP (right) binding at varying concentrations to SiaD. SiaC specifically interacted with SiaD with a KD of 24.7nM, whereas SiaCP failed to interact with SiaB. Shown are measured binding responses (black) and curve fits to a 1:1 interaction (red). Plots are representative from two experiments with similar results. RU, response units; KD, dissociation constant 