A helical, polymeric extracellular protein associated with the luminal surface of Haemonchus contortus intestinal cells.

The structure of the intestinal cells of the parasitic nematode Haemonchus contortus is described. The cells have numerous microvilli about 0-09 micron in diameter; most being 5-5-7-5 micron in length. The microvillar (plasma) membrane is coated with a layer of amorphous material (glycocalyx) about 60 A thick which is electron dense in sectioned preparations. Associated with the surface of this material, and filing the spaces between the microvilli, are filaments in the form of helices about 400 A in diameter and of variable pitch. The helices appear to be flexible but they are aligned approximately with the long axes of the microvilli. There are up to ten helices per microvillus; they extend beyond the tips of the microvilli and are up to 10 micron long. The material has been obtained nearly pure in small amounts. It is primarily protein and it is proposed that it should be called contortin. The monomeric form (of molecular weight about 60,000) has been identified with a Y-shaped structure with arms about 45 A long and 25 A wide seen in negatively stained preparations. The helical filament appears to be formed by lateral polymerization of patirs of these units.