Question

In E. coli, maltose-binding protein binds maltose in the periplasm to deliver the sugar to a maltose ABC transporter. Maltose-binding protein is a simple monomeric protein. It is 20% saturated when the maltose concentration is 300 nM. What is the Ko of maltose-binding protein for its ligand? A. 300 nM B. 600 nM C. 900 nM D. 1200 nM E. 1500 nM

Answer 1

Ans) The formula for monomeric protein binding with single ligand is $\Theta$ =

1 +PY

                                                                                                          

Where $\Theta$ = Binding affinity of ligand for the protein (Here given as 20% or 0.2)

L = Ligand concentration (Here given as 300nM)

Kd = Equilibrium dissociation constant (To be found out)

Substituting the values in the formula we get :

0.2 =

300 Kd + 300

$\therefore$ 0.2 (Kd + 300) = 300

$\therefore$ 0.2Kd + 60 = 300

$\therefore$ 0.2Kd = 240

$\therefore$ Kd = 240/0.2 = 1200nM

$\therefore$ The Kd of maltose binding protein for its ligand is 1200 nM.