The program OLIGOMER fits an experimental scattering curve from a multicompoment mixture of proteins to find the volume fractions of each component in the mixture.
The input data for oligomer is experimental SAXS or SANS scattering curve from a mixture of several dictinct components and a set of form-factors for each component of this mixture.
The experimental scattering intensity I(s) from a mixture of K different particles (components) is written as:
I(s) = ∑(wi×Ii(s))
where wi and Ii(s) are the volume fraction and the scattering intensity from the i-th component, respectively.
Given the intensities from the components (form-factors), OLIGOMER finds the volume fractions by solving a system of linear equations using the algorithm of nonnegative or unconstrained least-squares to minimize the discrepancy between the experimental and calculated scattering curves.
X-ray or neutron form-factors of proteins with known structure or of dummy atoms models can be computed using the programs CRYSOL and CRYSONrespectively, which both are part of the ATSAS package.