Interaction of proteins with spherical polyelectrolyte brushes in solution as studied by small-angle x-ray scattering

Abstract

We use small-angle x-ray scattering (SAXS) as a tool to study the binding of proteins to spherical polyelectrolyte brushes (SPB) in situ. The SPB consists of a solid core of approximately 100 nm diam onto which long polyelectrolyte chains [poly(styrene sulfonic acid, PSS) and poly(acrylic acid, PAA)] have been densely grafted. The proteins used in this investigation, Bovine Serum Albumine (BSA) and Bovine Pancreatic Ribonuclease A (RNase A), adsorb strongly to these SPB if the ionic strength is low despite their negative charge. Virtually no adsorption takes place at high ionic strength. SAXS demonstrates that both proteins are distributed within the brush. The findings reported here give further evidence that the strong adsorption of proteins to SPB is due to the "counterions release forces": The patches of positive charge on the surface of the proteins become multivalent counterions of the polyelectrolyte chains. Thus, a concomitant number of co- and counterions is thereby released and the entropy of the entire system is increased. The repulsive Coulombic interaction as well as the steric repulsion between the proteins and the brush layer are counterbalanced by this effect. The data discussed here demonstrate that the adsorption of proteins in SPB presents a new principle for the immobilization of proteins.

Thermoresponsive behavior of micellar aggregates from end-functionalized PnBA-b-PNIPAM-COOH block copolymers and their complexes with lysozyme

“…1,2 Small angle scattering methods and analysis advancements has pushed the field forward by characterizing in detail not only the morphology of protein binding nanoparticles e.g. spherical polyelectrolyte brushes, but also the location of adsorbed protein globules 3 . In other works contrast variation and selective labeling in small angle neutron scattering (SANS) has been exploited to define the conformational alterations of both the macromolecular and protein component during interaction 4 .…”

Directed Motion of Proteins along Tethered Polyelectrolytes

“…The analysis of SAXS intensity as a function of time provides the information about the amount and the position of the proteins within the polyelectrolyte layer [16]. The background subtracted intensity Iq can be split into the intensity I 0 q of a single particle and the structure factor Sq describing the mutual interaction between particles:…”

“…Sq can be obtained by an interaction site integral equation theory [17] that models the repulsive interaction between SPB. I 0 q of the SPB involves two parts, namely, I CS q that describes the core-shell structure of the particle and a second term I fluct q that takes into account the additional scattering contribution from the density fluctuations of the polyelectrolyte layer [16]. I CS q B 2 q, where Bq is the scattering amplitude given by…”

“…The analysis of the scattering intensity Iq can be done by dividing the q range into three parts [16]: At lowest q values (q 0:03 nm ÿ1 ) the interaction between the particles in solution, that is Sq [cf. Eq.…”

“…This part of Iq will be treated further below. At intermediate scattering angles (0:03 q 0:5 nm ÿ1 ) the adsorbed proteins do not manifest as individual units and the uptake of protein essentially increases r [16]. Hence, the term I CS q for q > 0:03 nm ÿ1 can be treated as in the case of unloaded particles.…”