Ion and ligand interactions of hyaluronic acid

University Of California-Santa Barbara, Santa Barbara CA

Investigators

Abstract

NONTECHNICAL ABSTRACT Hyaluronic acid is a biological molecule with a range of functions. It is an integral component of cartilage, where it plays a biomechanical role in promoting healthy joint function. Further, since it can be obtained in large quantities, and can be chemically modified, it has become widely studied for biomedical and biomaterial applications. These biological and technological roles rely on hyaluronic acid’s physical features: it is a long, linear polymer that is highly charged and water soluble, and it has a variety of interactions, both with salt ions and with biomolecular binding partners, that modify its structure and behavior. However, compared to other biopolymers (such as DNA or cytoskeletal components), the basic physical behavior of hyaluronic acid has not been extensively studied. The main goal of the present project is to perform precision measurements of the physical behavior of hyaluronic acid, and its modification by ions and other molecules. The researchers will carry out such experiments using modern biophysical approaches, and interpret them using advanced theoretical methods. Experiments will be focused on two areas: first, researchers will quantify electrostatic effects of salt on hyaluronic acid behavior, and particularly pursue understanding of physiologically-relevant mixed-salt conditions on molecular shape. Second, researchers will investigate the hypothesis that dramatic shape-changes can be induced in hyaluronic acid upon binding to specific biomolecular partners. Overall, the scientific work in this project will result in direct, quantitative estimates of the role of salt and biomolecular-binding in affecting hyaluronic acid behavior; in turn, this will lead to better understanding of the molecule’s various biological roles, and will permit rational engineering of hyaluronic acid in biomaterials environments. These scientific impacts are complemented by a range of other benefits, notably including a major effort to broaden graduate-student training through an exchange program with a German university, focused on teaching modern computational methods to bioengineers and biophysicists. Other benefits will accrue from collaboration with a national lab, and enhancing STEM human resources through undergraduate student training.   TECHNICAL ABSTRACT Hyaluronic acid, HA, is a long, linear, negatively-charged polysaccharide with moderate conformational flexibility. It plays broad biological roles, particularly in defining the mechanical and viscoelastic properties of extracellular spaces. HA’s properties have also led to broad investigation of its use as a synthetic biomaterial, e.g. forming injectables or cell/tissue growth substrates. The polymeric properties of HA underlie these biological and biotechnological roles, but are understudied. The overarching goal of this proposal is to fill that gap in knowledge by performing high-resolution physical measurements, supported by advanced theoretical interpretation methods, of ion- and ligand-induced HA conformational behaviors. The researchers will apply a unique single-molecule mechanics instrument to carry out precision measurements of HA’s solution-mediated conformational and mechanical properties. Specific goals include 1) exploiting machine-learning methods to improve instrument capabilities in screening biomolecular elasticity; 2) validating and exploring a recent finding that HA conformation in mixed-ionic conditions is dominated by an ‘ion jacket’ that screens the effect of bulk salt concentration; and 3) studying the effects of specific biological ligands on HA conformation, with a focus on ligands posited to induce a helix/coil transition in the chain, and those that cause global chain swelling. Experimental results will be interpreted with reference to analytical theories of solution electrostatics and polymer bottle-brush behavior, as well as coarse-grained molecular dynamics simulations. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.