Web Release Date: October 4,
Molecular Orientation of Membrane-Anchored Mucin Glycoprotein Mimics
and
Department of Chemistry, University of California, Berkeley, California 94720, Physical Bioscience and Materials Science Divisions, Lawrence Berkeley National Laboratory, Berkeley, California 94720, and Department of Molecular and Cell Biology, and Howard Hughes Medical Institute, University of California, Berkeley, California 94720
Received: March 16, 2007
In Final Form: July 20, 2007
Abstract:
Mucin glycoproteins contribute to a wide range of cell-surface phenomena. Their dense glycosylation is believed
to confer structural rigidity as well as molecular extension beyond the glycocalyx, crucial to interaction with
the cellular environment. However, controlled investigations of the relationships between glycosylation, rigidity,
and extension of membrane-bound mucins or similar macromolecules are lacking, largely because of the
absence of tractable experimental models. We have therefore made use of recently developed synthetic mucin
mimetics, in which the core 
-GalNAc monosaccharides of natural mucins are conjugated to a lipidated
polymer backbone and anchored to fluid, solid-supported lipid membranes, and fluorescence interference
contrast microscopy, an optical technique that provides nanometer-scale topographic information about objects
near a reflective interface, to measure the orientation of the mucin mimics relative to the membrane plane.
Data from two independent probes, fluorophores conjugated directly to the polymer backbone and fluorescent
proteins bound to the sugar groups, unexpectedly show that the mucin mimic molecules lie flat along the
membrane. Rigidity and core glycosylation are therefore insufficient to ensure molecular projection outward
from a membrane surface.
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