(383d) Strong Repulsive Forces between Protein and Phosphocholine Self-Assembled Monolayers - a Molecular Simulation Study

Phosphocholine terminated self-assembled monolayer (PC-SAM) is an extensively used class of surfaces which render protein resistant. Unlike oligo (ethylene glycol) self-assembled monolayer (OEG-SAM), the nonfouling property of which is attributed to the strong hydrogen bonding of water molecules to the surface and the conformational flexibility of the chain, the nonfouling mechanism of PC-SAM is still poorly understood due to complicate interplay of various among protein, solvents and surfaces, especially the complex hydration of lipid headgroups. Except for abundant hydrogen bonding donors in phosphorus head groups, PC-SAM also have strong electrostatic interaction with water due to its zwitterionic nature, which indicates that the nonfouling mechanism of PC-SAM is quite different to that of OEG-SAM. In this work, we performed all atom restrained molecular simulation to study the interaction between lysozyme and PC-SAM with explicit water and ions with our BIOSURF program. The structure of water at PC-SAM/water interface was analyzed to provide molecular-level information for the interpretation of our simulation and experimental results. We compared properties of water at both oligo (ethylene glycol) self-assembled monolayer (OEG-SAM) and PC-SAM. It was found the dynamic behavior of water at PC-SAM was significantly different from those at OEG-SAM. The former exhibits a faster reorientational dynamics than the latter, while both of them show similar translational dynamics. These dynamic properties prove the different nature of these two SAM surfaces and contribute to a comprehensive understanding of the nonfouling mechanism.