Direct Evidence of Controlled Structure Reorganization in a Nanoorganized Polypeptide Multilayer Thin Film

Abstract

Aspects of poly(l-lysine) (PLL) and poly(l-glutamic acid) (PLGA) multilayer thin film assembly, physical properties of the films, and changes in film structure on pH shift have been studied by far-UV circular dichroism spectroscopy (CD), ultraviolet spectroscopy (UVS), ellipsometry, quartz crystal microbalance (QCM), and atomic force microscopy (AFM). We show that CD can be used to assess the secondary structure content of a polypeptide multilayer film deposited on quartz substrates by electrostatic layer-by-layer assembly (LbL). Measurements have revealed that, under conditions where PLL and PLGA displayed a random coillike conformation in solution, the polypeptides formed predominantly β-sheet structures in multilayer films fabricated by LbL. A substantial conformational change occurred on exposure of such films to a strongly acidic (pH ≤ 2.5) or strongly basic (pH ≥ 12.0) aqueous medium, from β-sheet to predominantly α-helical structure. pH shift thus may be a useful postpreparation approach for stimuli-responsive modification of the surface roughness, porosity, and permeability of preassembled polypeptide films or structures made from such films, e.g., microcapsules.

Branched polymer models and the mechanism of multilayer film buildup

“…All of the CD spectra have a roughly similar shape. This implies that the peptides in all six films had approximately the same backbone structure and that all contained a significant proportion of residues in the same conformation, ␤ sheet [25,31,33,40], consistent with interpretation of Fourier-transform infrared spectra of polypeptide multilayer films [22,31,32].…”

“…In Ref. [40], the average peak height of a 10-layer PLL (84 kDa)/PLGA (84.6 kDa) film prepared at pH 7.4 was less than 3.5 nm after dehydration. The values compare favorably with the results of the present study (Table 2).…”

“…Established methods of making MAPs were convenient for producing branched structures. PLL and PLGA were selected because they are the most common polypeptides in multilayer film studies [17,18,20,25,28,32,[39][40][41][42][43]. Both polymers are also said to diffuse in multilayer films and, according to the "in and out diffusion" hypothesis, give rise to exponential growth [18,20,21,28,29].…”

Polypeptide multilayer nanofilm artificial red blood cells

“…Indeed, we have demonstrated that control over peptide sequence represents a means of control over useful film properties. [42][43][44] Assembly behavior of given polypeptides in a multilayer film will depend on propensity to form secondary structure, pH, ionic strength, presence of cosolvents, and so on. The broad range of process control variables enables the engineering of physical, chemical, and biological properties of multilayer filmbased structures.…”

A survey of the 2001 to 2005 quartz crystal microbalance biosensor literature: applications of acoustic physics to the analysis of biomolecular interactions

“…The ability of QCM to monitor viscoelastic changes in a molecule has been exploited to study the kinetic profile of absorption and associated conformational change of lysozyme on various surfaces (Shen et al, 2001), the role of hydration on the mechanism of allosteric regulation by in situ measurements of the oxygen-linked kinetics of water binding to haemoglobin (Salvay et al, 2003a(Salvay et al, , 2003b) and the density of protein (Voros, 2004) and peptide (Zhi and Haynie, 2004) layers subject to partial denaturation. QCM was used in the study of the coiled-coil protein motif, which occurs in over 200 proteins and which is of particular interest for a range of applications requiring surface immobilization of the constituent peptides (Stevens et al, 2004).…”