title: Control of the molecular orientation of membrane-anchored biomimetic glycopolymers.
abstract: Quantifying and controlling the orientation of surface-bound macromolecules is crucial to a wide range of processes in areas as diverse as biology, materials science, and nanotechnology. Methods capable of directing orientation, as well as an understanding of the underlying physical mechanisms are, however, lacking. In this paper, we describe experiments in which the conformations of structurally well-defined polymers anchored to fluid lipid membranes were probed using Fluorescence Interference Contrast Microscopy (FLIC), an optical technique that provides topographic information with few-nanometer precision. The novel rodlike polymers mimic the architecture of mucin glycoproteins and feature a phospholipid tail for membrane incorporation and a fluorescent optical probe for FLIC imaging situated at the opposite termini of the densely glycosylated polymeric backbones. We find that the orientation of the rigid, approximately 30 nm long glycopolymers depends profoundly on the properties of the optical reporter. Molecules terminated with Alexa Fluor 488 projected away from the lipid bilayer by 11 +/- 1 nm, consistent with entropy-dominated sampling of the membrane-proximal space. Molecules terminated with Texas Red lie flat at the membrane (height, 0 +/- 2 nm), implying that interactions between Texas Red and the bilayer dominate the polymers' free energy. These results demonstrate the design of macromolecules with specific orientational preferences, as well as nanometer-scale measurement of their orientation. Importantly, they reveal that seemingly minute changes in molecular structure, in this case fluorophores that comprise only 2% of the total molecular weight, can significantly alter the molecule's presentation to the surrounding environment.
authors: Department of Chemistry, University of California, Berkeley, California 94720, USA.
authors: Kamil
authors: K
authors: Godula
authors: Marissa L
authors: ML
authors: Umbel
authors: David
authors: D
authors: Rabuka
authors: Zsofia
authors: Z
authors: Botyanszki
authors: Carolyn R
authors: CR
authors: Bertozzi
authors: Raghuveer
authors: R
authors: Parthasarathy
mesh_terms: D040761:Biomimetic Materials / Q000138:chemical synthesis / Q000737:chemistry*; D006031:Glycosylation; D008051:Lipid Bilayers / Q000737:chemistry; D008567:Membranes, Artificial; D008968:Molecular Conformation; D015394:Molecular Structure; D009077:Mucins / Q000138:chemical synthesis / Q000737:chemistry; D010316:Particle Size; D011108:Polymers / Q000138:chemical synthesis / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D008051:Lipid Bilayers; D008567:Membranes, Artificial; D009077:Mucins; D011108:Polymers