How high concentrations of proteins stabilize the amorphous state of calcium orthophosphate: a solid-state NMR study of the casein case.
Related Articles How high concentrations of proteins stabilize the amorphous state of calcium orthophosphate: a solid-state NMR study of the casein case.
Langmuir. 2017 Jan 17;:
Authors: De Sa Peixoto P, Silva JV, Laurent GP, Schmutz M, Thomas D, Bouchoux A, Gesan-Guiziou G
Abstract
Understanding how proteins stabilize Amorphous Calcium ortho-Phosphate (ACP) phases is of great importance in biology and for pharmaceutical or food applications. Until now, most of the former investigations about ACP-protein stability and equilibrium were performed in conditions where ACP colloidal nanoclusters are surrounded by low to moderate concentrations of peptides or proteins (15-30 g.L-1). As a result, the question of ACP-protein interactions in highly concentrated protein systems has clearly been overlooked, whereas it corresponds to actual industrial conditions such as drying or membrane filtration in the dairy industry for instance. In this study, the structure of an ACP phase is moni-tored in association with one model phosphorylated protein (casein) using solid state NMR (ssNMR) at two conditions of high protein concentration (300 and 400 g.L-1). At both con-centrations and at 25°C, it is found that the caseins maintain the mineral phase in an amorphous form with no detectable influence on its structure or size. Interestingly, and in both cases, a significant amount of the non-phosphorylated side chains interacts with ACP through H-bonds. The number of these interacting side-chains is found to be higher at the high-est casein concentration. At 45°C, which is a destabilizing temperature of ACP in protein-free conditions, the amorphous structure of the mineral phase is partially transformed at 300 g.L-1 while it remains almost intact at 400 g.L-1. These results thus clearly indicate that rising the concentration of proteins favor protein-ACP interactions and stabilize the ACP clusters more efficiently.
PMID: 28094949 [PubMed - as supplied by publisher]
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