The interaction of chondroitin sulfate with a lipid monolayer observed by using nonlinear vibrational spectroscopy.

Kevin Pagel,Rebecca L. Miller,Szilvia Krekic,Mark Mero,Gergo Peter Szekeres,Zsuzsanna Heiner

doi:10.1039/d1cp01975a

Abstract

The first vibrational sum-frequency generation (VSFG) spectra of chondroitin sulfate (CS) interacting with dipalmitoyl phosphatidylcholine (DPPC) at air–liquid interface are reported here, collected at a laser repetition rate of 100 kHz. By studying the VSFG spectra in the regions of 1050–1450 cm−1, 2750–3180 cm−1, and 3200–3825 cm−1, it was concluded that in the presence of Ca2+ ions, the head groups together with the head-group-bound water molecules in the DPPC monolayer are strongly influenced by the interaction with CS, while the organization of the phospholipid tails remains mostly unchanged. The interactions were observed at a CS concentration below 200 nM, which exemplifies the potential of VSFG in studying biomolecular interactions at low physiological concentrations. The VSFG spectra recorded in the O–H stretching region at chiral polarization combination imply that CS molecules are organized into ordered macromolecular superstructures with a chiral secondary structure.

Highlights

Glycosaminoglycans (GAGs) are linear, negatively charged polysaccharides, whose analysis and, understanding are greatly challenged by their high heterogeneity in chain length, degree of sulfation, and the resulting sulfation pattern
The surface pressure of the dipalmitoyl phosphatidylcholine (DPPC) monolayer, serving as a simple membrane model, was chosen to be B30 mN mÀ1 (ESI,† Fig. S1) to stay close to the surface pressure measured in cell membranes.[19]
The spectra cover most of the fingerprint, C–H stretching, and O–H stretching spectral regions in both polarization combinations, providing comprehensive information about the interfacial molecular groups corresponding to water, DPPC, and chondroitin sulfate (CS)

Summary

Introduction

Glycosaminoglycans (GAGs) are linear, negatively charged polysaccharides, whose analysis and, understanding are greatly challenged by their high heterogeneity in chain length, degree of sulfation, and the resulting sulfation pattern. Paper recently been enormous progress in techniques to produce homogeneous GAG chains for detailed structural studies.[12] An increasing number of studies on lipid–GAG interactions and with that a considerable gain of knowledge is expected in the years. Secondary structures of peptides and proteins were increasingly investigated by chiral VSFG spectroscopy demonstrating the potential of this technique in revealing macromolecular structures and orientations at biological interfaces at the fundamental level in situ and in real time.[13] Recent progress in laser technology made it possible to increase the laser repetition rate by two orders of magnitude to 100 kHz,[14,15] which in turn led to a drastic increase in signal-tonoise ratio and a shorter acquisition time (r10 s) in VSFG spectroscopic studies of solid-supported phospholipid monolayers.[16,17]

Methods

Results

Conclusion