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Infection and Immunity, July 2000, p. 4217-4224, Vol. 68, No. 7
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

The Most Abundant Glycoprotein of Amebic Cyst Walls (Jacob) Is a Lectin with Five Cys-Rich, Chitin-Binding Domains

Marta Frisardi,1 Sudip K. Ghosh,1 Jessica Field,1 Katrina Van Dellen,1 Rick Rogers,2 Phillips Robbins,3 and John Samuelson1,*

Department of Immunology and Infectious Diseases1 and BioMedical Imaging Institute,2 Harvard School of Public Health, and Department of Cell Biology, Boston University School of Dental Medicine,3 Boston, Massachusetts

Received 31 January 2000/Returned for modification 1 March 2000/Accepted 25 March 2000

The infectious stage of amebae is the chitin-walled cyst, which is resistant to stomach acids. In this study an extraordinarily abundant, encystation-specific glycoprotein (Jacob) was identified on two-dimensional protein gels of cyst walls purified from Entamoeba invadens. Jacob, which was acidic and had an apparent molecular mass of ~100 kDa, contained sugars that bound to concanavalin A and ricin. The jacob gene encoded a 45-kDa protein with a ladder-like series of five Cys-rich domains. These Cys-rich domains were reminiscent of but not homologous to the Cys-rich chitin-binding domains of insect chitinases and peritrophic matrix proteins that surround the food bolus in the insect gut. Jacob bound purified chitin and chitin remaining in sodium dodecyl sulfate-treated cyst walls. Conversely, the E. histolytica plasma membrane Gal/GalNAc lectin bound sugars of intact cyst walls and purified Jacob. In the presence of galactose, E. invadens formed wall-less cysts, which were quadranucleate and contained Jacob and chitinase (another encystation-specific protein) in secretory vesicles. A galactose lectin was found to be present on the surface of wall-less cysts, which phagocytosed bacteria and mucin-coated beads. These results suggest that the E. invadens cyst wall forms when the plasma membrane galactose lectin binds sugars on Jacob, which in turn binds chitin via its five chitin-binding domains.

* Corresponding author. Mailing address: Department of Immunology and Infectious Diseases, Harvard School of Public Health, 665 Huntington Ave., Boston, MA 02115. Phone: (617) 432-4670. Fax: (617) 738-4914. E-mail: jsamuels{at}hsph.harvard.edu.

Infection and Immunity, July 2000, p. 4217-4224, Vol. 68, No. 7
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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