Investigating the Sequence Specific Adsorption Behavior of Polypeptides at the Solid/Liquid Interface

Abstract

Polymer adsorption at the solid/liquid interface depends not only on the chemical composition of the polymer but also on the specific placement of the monomers along the polymer sequence. However, challenges in designing polymers with well-controlled sequences have limited explorations into the role of polymer sequence on adsorption behavior to molecular simulations. Here, we demonstrate how the sequence control offered by polypeptide synthesis can be utilized to study the effects small changes in polymer sequence have on polymer adsorption behavior at the solid/liquid interface. Through a combination of quartz crystal microbalance with dissipation monitoring and total internal reflection ellipsometry, we study the adsorption behavior of three polypeptides, consisting of 90% lysine and 10% cysteine, onto a gold surface. We find different mechanisms are responsible for the adsorption of polypeptides and the resulting conformation on the surface. The initial adsorption of the polypeptides is driven by electrostatic interactions between the polylysine and the gold surface. Once adsorbed, the cysteine undergoes a thiol–Au reaction with the surface, altering the conformation of the polymer layer. Our findings suggest the conformation of the polypeptide layer is dependent on the placement of the cysteines within the sequence; polypeptide chains with evenly spaced cysteine groups adopt a more tightly bound “train” conformation as compared to polypeptides with closely grouped cysteine groups. We envision that the methodologies presented here to study sequence specific adsorption behaviors using polypeptides could be a valuable tool to complement molecular simulations studies.

Exploring Enzymatic Conformational Dynamics at Surfaces through μ-FTIR Spectromicroscopy

“…26 The influence of electrostatic and hydrophobic interactions in the protein/ surface interface is determinant to the coffee-ring pattern formation, making this phenomenon a vital subject of study as it directly influences many applications, such as protein microarrays 26,27 and cell patterning. 28 Despite recent advances highlighting conformational differences of proteins in solution and immobilized, as the sequence adsorption specificity, 29 modelings of occupancy and conformational changes, 30 and exploring vibrational data multivariate analysis, 22 there are mechanistic and phenomenological knowledge gaps to be addressed and in situ monitoring of protein−surface interactions can provide additional informa-tion to deepen current comprehension of interfacial interplays, such as the spatial visualization of vibrational dynamics of proteins differentially adsorbed within a coffee-ring morphological formation. Herein, we report the use of FTIR spectromicroscopy (μ-FTIR) to probe the interaction of a model protein with three commonly employed and diverse solid matrices regarding structural conformation changes in a coffee-ring formation situation: gold, thioglycolic acid-coated gold, and calcium fluoride.…”