Nonfreezing Water Structuration in Heteroprotein Coacervates

Abstract

Surface-bound water in protein solutions has been identified with a reduction in its freezing point. We studied the presence of such nonfreezing water (NFW) in various protein-polyelectrolyte, micelle-polyelectrolyte, and protein-protein (heteroprotein) coacervates, along with appropriate concentrated solutions of macromolecules alone, finding up to 15% w/w NFW for the heteroprotein coacervate of lactoferrin (LF) and β-lactoglobulin (BLG). The level of NFW is always higher in coacervates than in the control (single macromolecule) systems, particularly for protein-containing coacervates: a coacervate of bovine serum albumin (BSA) and poly(dimethyldiallylammonium chloride) (PDADMAC) showed a ratio of NFW/protein twice that of BSA alone (0.6 vs 0.3), with a similarly high ratio for LF-BLG coacervate. These results are attributed to the maximization of water-protein contacts, structural features that reflect the mode of sample assembly, as they are not seen in a noncoacervated LF-BLG solution with identical concentrations of all species.

Molecular and structural basis of low interfacial energy of complex coacervates in water

“…Despite significant interest in and importance of the low interfacial tension of complex coacervate fluids, as highlighted, few systematic experimental studies exist that report on its physical basis, and even fewer that comprehensively combine experiments and theoretical considerations [54,74,[98][99][100]. We will highlight one most recent example published by the authors that showcase how one can gain access to key physical properties of complex coacervate fluids.…”

Recent progress in the science of complex coacervation

“…For instance, calorimetry measurements have suggested that the "non-freezing water" content of protein-based coacervates could be as high as 15% w/w. 89 4. The solvent is assumed to be a continuum.…”

“…To date, the majority of approaches rely on indirect phenomenological measurements such as changes in the phase behavior of coacervates, 40,64,139 differences in the amount of water introduced into a sample by different ions, 53 or measurements of "non-freezing," surface-bound water. 89 Experimentally, new techniques such as terahertz dielectric spectroscopy have the potential to help directly access these structural changes, 149,150 and these questions look to be key to future materials design questionseven beyond coacervation.…”

Heteroprotein complex coacervation: A generic process

“…At low temperature (e.g. 5°C), the hydrophobic tail dissociates leading to monomeric complexes formed by one LF and one concentration [68]. These authors suggest that protein assemblies constituting the coacervates maximize protein-water interactions.…”