Binding of R2 to A

The ScbR homo-dimer (R₂) forms a complex with ScbA (A).

Chemical equation

$A + R_{2} \rightleftharpoons A-R_{2}$

Rate equation

$r= \frac{k^{-}_{3}}{K_{d3}}\cdot [A]\cdot [R_{2}] - k^{-}_{3}\cdot [A-R_{2}]$

Parameters

The parameters of this reaction are the dissociation constant for binding of ScbR to ScbA ($K_{d3}$) and the dissociation rate for binding of ScbR to ScbA ($k^{-}_{3}$). Since no evidence of the existence of the ScbA-ScbR complex has been found so far, our belief is that the interaction between the two proteins should be an unstable/ transient. The values of such complexes according to the literature , lie in the millimolar or micromolar scale.

Parameter	Value	Units	Origin	Remarks
$K_{d3}$	$10^{3} - 10^{9}$	$nM$	Comparison of strong vs weak protein-protein interactions	Range of values that correspond to weak protein interactions
$k^{-}_{3}$	$0.6-1.2 min^{-1}$	$min^{-1}$	Generalistic mechanisms of protein-protein interaction

Parameters with uncertainty

The most plausible parameter values and the confidence interval were decided to be:

$K_{d3} = 10^{3} \pm 10 nM$

$k^{-}_{3}= 0.9 \pm 0.3 min^{-1}$

The probability distributions, adjusted accordingly in order to reflect the above values, are the following: