Rodlike Complexes of a Polyelectrolyte (Hyaluronan) and a Protein (Lysozyme) observed by SANS

TL;DR

This study uses Small Angle Neutron Scattering to investigate the structure of hyaluronan-lysozyme complexes, revealing rod-like formations that depend on molecular weight and concentration, advancing understanding of biopolymer-protein interactions.

Contribution

It provides the first direct SANS evidence of rod-like hyaluronan-lysozyme complexes and describes their structural characteristics based on molecular weight and phase conditions.

Findings

Rod-like complexes form near phase separation onset.

Large molecular weight complexes extend beyond HA persistence length.

Short chains form complexes close to their contour length.

Abstract

We study by Small Angle Neutron Scattering (SANS) the structure of Hyaluronan -Lysozyme complexes. Hyaluronan (HA) is a polysaccharide of 9 nm intrinsic persistence length that bears one negative charge per disaccharide monomer (Mmol = 401.3 g/mol); two molecular weights, Mw = 6000 and 500 000 Da were used. The pH was adjusted at 4.7 and 7.4 so that lysozyme has a global charge of +10 and + 8 respectively. The lysozyme concentration was varied from 3 to 40 g/L, at constant HA concentration (10 g/L). At low protein concentration, samples are monophasic and SANS experiments reveal only fluctuations of concentration although, at high protein concentration, clusters are observed by SANS in the dense phase of the diphasic samples. In between, close to the onset of the phase separation, a distinct original scattering is observed. It is characteristic of a rod-like shape, which could characterize "single" complexes involving one or a few polymer chains. For the large molecular weight (500 000) the rodlike rigid domains extend to much larger length scale than the persistence length of the HA chain alone in solution and the range of the SANS investigation. They can be described as a necklace of proteins attached along a backbone of diameter one or a few HA chains. For the short chains (Mw ~ 6000), the rod length of the complexes is close to the chain contour length (~ 15 nm).