The CEACAM1 N-terminal Ig domain mediates cis- and trans-binding and is essential for allosteric rearrangements of CEACAM1 microclusters

Klaile, Esther; Vorontsova, Olga; Sigmundsson, Kristmundur; Müller, Mario M.; Singer, Bernhard B.; Öfverstedt, Lars-Göran; Svensson, Stina; Skoglund, Ulf; Öbrink, Björn

In addition to Eq. 1.2 and the relation [A 2 ] = [A] 2 /K D , which provide the bulk concentrations of the monomer and dimer forms for a given A Total , the curve-fit model is composed of the following coupled differential equations, applied for numerical integration: (1.5) 2. Formation of two classes of dimers (types 1 and 2) by two different homophilic binding sites. By the introduction of a second binding site in the monomer, two more variables, k a2 and k d2 , need to be accounted for. At all conditions, it holds for the analyte (given in grams/liter) that Of the three solutions to the cubic equation, two involve complex numbers, and therefore, with regard to our model, have no physical relevance. The third one is a real number solution, which is relevant for addressing the monomer concentration in the sample (i.e., analyte), yielding However, this solution is rather fragile if applied on a real number format to curve-fit algorithms because of somewhat complicated variable compositions within the root terms. For this reason, subfunctions for these terms are better defined as complex number functions when applied together with such algorithms.