Journal of Cell Science, Vol 100, 707-715, Copyright © 1991 by Company of Biologists

Submitted on April 25, 1991
Accepted on July 12, 1991

The Membrane Skeleton of Pseudomicrothorax

II. Biochemical and Immunological Characterization of the Glycosylated Cytoskeletal Proteins

¹ Department of Zoology and Animal Biology, University of Geneva, 30, Quai Ernest-Ansermet, 1211 Geneva 4, Switzerland: Gartenstrasse 28, D-3400 Gottingen, FRG
² Department of Zoology and Animal Biology, University of Geneva, 30, Quai Ernest-Ansermet, 1211 Geneva 4, Switzerland

The membrane skeleton, or epiplasm, is part of the structurally complex ciliate cortex. It is thought to have skeletal functions concerning the spatial organization of cortical elements such as the basal bodies.

Here we report the biochemical and immunological characterization of some components of the purified epiplasm of Pseudomicrothorax dubius. The epiplasm proteins consist of two quantitatively major groups of proteins, one of 76-80x10³ M_r, the other of 11-13x10³ M_r, which appear to be the principal structural elements of the epiplasm, and a series of minor components of 62-18x10³ M_r. Based upon lectin labeling and glycosidase treatment, some of the latter have been identified as glycoproteins. Using affinity-purified antibodies specific for individual glycoproteins or groups of glycoproteins, we were able to localize them in situ by immunoelectron microscopical methods. This in situ localization demonstrates that the glycosylated epitopes, unlike the glycoresidues of membrane proteins, are distributed throughout the entire epiplasmic layer rather than being restricted to regions adjacent to the cortical membranes. Thus, these proteins represent glycosylated, cytoskeletal elements. At least one of these glycoproteins (M_r 62x10³) shows positive immunoreactivity with a monoclonal antibody (Pruss anti-IFA) recognizing most intermediate filament (IF) proteins, indicating that IF proteins might be present in protozoan cytoskeletons.

Key words: ciliophora, cytoskeleton, glycoproteins, intermediate filament proteins, protozoa, anti-IFA, Pseudomicrothorax

Submitted on April 25, 1991
Accepted on July 12, 1991

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