Classification of protein binding in hydroxyapatite chromatography: synergistic interactions on the molecular scale.

A protein library exhibiting a range of properties was employed to study protein binding behavior in hydroxyapatite systems. Chromatographic retention on ceramic hydroxyapatite (CHT) chromatography was determined using a sodium chloride gradient in the presence of different phosphate concentrations. Results from the column experiments were then analyzed using various quantitative structure property relationship (QSPR) based modeling approaches. Using the experimental data set in concert with new molecular descriptors, QSPR classification models were generated to provide improved understanding of protein binding in CHT systems. In addition, nonlinear SVM QSPR prediction models were generated and employed as a predictive tool for protein affinity in CHT. Interestingly, a class of descriptors which describe synergistic binding with both metal chelation and cation exchange interactions on the angstrom length scale was found to play a vital role for protein binding in all of the models developed for CHT. The importance of this descriptor suggests the importance of synergistic binding in CHT, which has not been previously described in the literature. This study provides a deeper understanding into the mechanisms and selectivity of protein adsorption in CHT and will help to create predictive models which could be used for methods development in bioseparation processes.