Salt doping of hyaluronic acid glycopolymer biocondensates.

Abstract

Biocondensates are largely studied with regard to intracellular components, while recognition of the formation of extracellular biocondensates are emerging, such as for cell surface heparan sulfate binding with basic fibroblast growth factor. This study analyzed the formation of biocondensates in vitro between the ubiquitous extracellular component, hyaluronan an anionic glycosaminoglycan, and cationic derivitized polyglucosamines known to bind to mucosal interfaces. The effect of molecular weight and net charge ratio was studied using a combination of microscopy, turbidity, laser diffraction particle sizing and zeta potential measurements. These analyses revealed that molecular weight affected the ability to form biocondensates while the surface composition of the condensates was altered by the net charge ratio of the macromolecules. The role of salt counterions in the biocondensate also shows trends of ion-pairing that are consistent with coacervate-salt-doping theory and a description of condensates as so-called complex coacervate micelles with surface brushes akin to soft colloidal particles. The salt type and concentrations are also observed to affect the condensate size and surface potential. An electrostatic model of the structures describes how ion-partitioning depends on the spatial variation of the dielectric permittivity to establish steady-state Born-hydration energy and electrostatic potential gradients. Together this study adds to our understanding of the formation of extracellular biomolecular condensates.