Casein macropeptide adsorption into a charged substrate: the impact of charge regulation

PABLO M. BLANCO; MICAELA M. ACHETONI; GARCÉS, JOSEP L.; CLAUDIO F. NARAMBUENA

Shanghai

Simposio; 13th International Symposium on Polyelectrolytes; 2021

East China University of Science and Technology Nanjing University of Science and Technology

Casein macropeptide (CMP) is one of the most abundant proteins in the milk whey with a concentration ranging from 1.2 to 1.5 g/L. The development of an efficient method to purify CMP from the milk whey is desirable since, in addition to the intrinsic nutritional value of CMP, CMP-free milk whey can be used for infant milk formulas. CMP is a short peptide composed of 64 aminoacids which exhibits a rich and complex physicochemistry. Similarly to weak polyampholytes, the structure of CMP has been found to be highly sensitive to the pH. In turn, the titration of CMP is not trivial, since it does not present an unique isoelectric point (pI) but a possible range of values ranging from 3.15 to 4.25 pH units. The reason for this heterogeneity is that CMP can undergo glycosylation reactions in the milk whey. These glycosylation reactions add additional sialic acid groups in the peptide chain, lowering the pI of CMP and causing the range of possible pI values observed. In this work, we use Semi-Grand Canonical Monte Carlo simulations to study the adsorption of CMP onto a charged substrate. We build on a previous model used to study the adsorption of weak polyelectrolytes on charged surfaces. We quantify the adsorption of a non-glycosylated CMP and a fully glycosylated CMP chain into differently charged substrates for different pH-values. In turn, we analyze how the CMP charge is regulated by the presence of the charged surface. These observations will allow the rational design of new experimental setups, pinpointing indicating the ideal conditions to purify CMP.