Adsorption Behavior of Acidic and Basic Proteins onto Citrate-Coated Au Surfaces Correlated to Their Native Fold, Stability, and pI

Abstract

The adsorption of eight different proteins (alpha-lactalbumin (types I and III), bovine serum albumin, hemoglobin, myoglobin, cytochrome c, alpha-casein, and lysozyme) onto a model anionic surface was performed at equivalent bulk (solvent, ionic strength, pH) and surface conditions. Adsorption was monitored on a quartz crystal microbalance with dissipation monitoring (QCM-D) with citrate-coated gold surfaces as adsorbents and has been correlated to native fold stability determined from near- and far-UV circular dichroism (CD) measurements. The proteins studied here were chosen based on their pI and documented knowledge about their structural stability and flexibility. Protein adsorption was found to be independent of global protein charge. Rather, binding occurs through oppositely charged patches on protein and surface. Moreover, data indicate that there is a correlation between secondary and tertiary structure stability and the adsorption characteristics at interfaces. Also, protein surface coverage, layer thickness, and flexibility can be tuned as a function of deposition method. This is discussed in terms of adsorption/spreading kinetics and intermolecular (protein-surface and protein-protein) interactions. Adsorption to surfaces can induce formation of supramolecular structures such as micelles (in the case of alpha-Cas) and multilayers (as for Hb). In the case of alpha-casein, this phenomenon depends on the deposition method and protein concentration. When ranking the surface coverage for proteins added in excess, the order is Lyz < Cyt c < Mb < BSA < alpha-La I < alpha-Cas < alpha-La III < Hb, which can be correlated to the proteins ability to form supramolecular structures (alpha-Cas, Hb), overall conformational flexibilities, and ability to form stable intermediates.

IgG and fibrinogen driven nanoparticle aggregation

“…The same trend has been observed for transferrin or serum albumin mixed with sulfonated polystyrene NPs [16,17], while other studies show that gold NPs are stabilized by serum albumin and cytochrome C [18][19][20][21]. Lysozyme, however, can induce the strong aggregation of silica, polystyrene, and gold NPs [17,[22][23][24][25], which also is observed when fibrinogen is incubated with polystyrene and silica NPs [26].…”

Three-way Interaction between 14-3-3 Proteins, the N-terminal Region of Tyrosine Hydroxylase, and Negatively Charged Membranes

“…8C shows conserved (blue) and non-conserved (white and red) residues within the three isoforms here studied, 14-3-3␥, -, and -; the red-highlighted non-conserved residues represent a charge change. As is the case for many proteins interacting with lipid membranes (34,62,68,69), the 14-3-3␥-membrane interaction takes place at pH values where this acidic protein is clearly negatively charged. A rough estimate gives an approximate global charge of Ϫ30 for the 14-3-3␥ dimer at pH 7.4, but at the same time, the protein binds to negatively charged membranes.…”

Nanoparticle‐stabilized microbubbles for multimodal imaging and drug delivery

“…Adsorption of proteins onto negatively charged NPs above the isoelectric point of the protein has been well documented [33,34]. Close to the pI, the electrostatic interaction is weak, and the protein will likely be randomly oriented at the NP surface, whereas at pH 7.5, protein orientation is dictated by charge density matching between oppositely charged domains.…”