Elucidating the Structure of the Glycocalyx-Microvilli Complex on the Surface of a Model Epithelia Cell Using Freeze-Etch and Electron Tomography

Authors

• WS Sun
• ES Krystofiak
• R Cui
• B Kachar

Abstract

Most epithelial and endothelial cell surfaces are covered by glycocalyx, a complex glycoprotein structure that serves a wide range of functions including hydration, filtration and protection against pathogens. The enteric glycocalyx lines the length of the intestinal tract and is central to both digestive and protective functions. However, very little is known about how the molecular architecture of the intestinal glycocalyx enables its proposed functions. Using a combination of freeze-etch and electron tomography, we were able to observe fine details of the intestinal glycocalyx organization in an unprecedented manner and describe the structure-function relationship. The intestinal glycocalyx is composed of 1 µm long columnar filaments that emerge from the distal ends of microvilli, forming a continuous layer on top of the laterally crosslinked-hexagonally packed brush border. The closely spaced columnar glycocalyx filaments show extensive anastomosing side-to-side interactions along their length over and across the surface of enterocytes, producing a dense meshwork with an averaged filament width of 8 nm. Most surprisingly, the termini of glycocalyx filaments come together to form a well-patterned cover net that displayed liquid hexagonal packing with center-to-center distance of 32 nm. The brush border, columnar glycocalyx filaments and the terminal cover net arrange into a stratified but highly integrated transcellular organization that maintains a regular structure across the intestinal epithelium. Our results provide a new structural framework for understanding how the glycocalyx-microvilli complex act as a molecular filter and function as a protective barrier while accommodating for intestinal homeostasis.

Scientific Focus Area: Cell Biology

This page was last updated on Friday, March 26, 2021