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Eukaryotic Cell, May 2006, p. 836-848, Vol. 5, No. 5
1535-9778/06/$08.00+0     doi:10.1128/EC.5.5.836-848.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Unique Posttranslational Modifications of Chitin-Binding Lectins of Entamoeba invadens Cyst Walls

Katrina L. Van Dellen,1 Anirban Chatterjee,1 Daniel M. Ratner,1,2 Paula E. Magnelli,1 John F. Cipollo,1 Martin Steffen,3 Phillips W. Robbins,1 and John Samuelson1,4*

Department of Molecular and Cell Biology, Boston University Goldman School of Dental Medicine, Boston, Massachusetts 02118,1 Section of Infectious Diseases, Boston Medical Center, Boston, Massachusetts 02118,2 Departments of Genetics and Genomics,3 Microbiology, Boston University School of Medicine, Boston, Massachusetts 021884

Received 17 January 2006/ Accepted 3 March 2006

Entamoeba histolytica, which causes amebic dysentery and liver abscesses, is spread via chitin-walled cysts. The most abundant protein in the cyst wall of Entamoeba invadens, a model for amebic encystation, is a lectin called EiJacob1. EiJacob1 has five tandemly arrayed, six-Cys chitin-binding domains separated by low-complexity Ser- and Thr-rich spacers. E. histolytica also has numerous predicted Jessie lectins and chitinases, which contain a single, N-terminal eight-Cys chitin-binding domain. We hypothesized that E. invadens cyst walls are composed entirely of proteins with six-Cys or eight-Cys chitin-binding domains and that some of these proteins contain sugars. E. invadens genomic sequences predicted seven Jacob lectins, five Jessie lectins, and three chitinases. Reverse transcription-PCR analysis showed that mRNAs encoding Jacobs, Jessies, and chitinases are increased during E. invadens encystation, while mass spectrometry showed that the cyst wall is composed of an ~30:70 mix of Jacob lectins (cross-linking proteins) and Jessie and chitinase lectins (possible enzymes). Three Jacob lectins were cleaved prior to Lys at conserved sites (e.g., TPSVDK) in the Ser- and Thr-rich spacers between chitin-binding domains. A model peptide was cleaved at the same site by papain and E. invadens Cys proteases, suggesting that the latter cleave Jacob lectins in vivo. Some Jacob lectins had O-phosphodiester-linked carbohydrates, which were one to seven hexoses long and had deoxysugars at reducing ends. We concluded that the major protein components of the E. invadens cyst wall all contain chitin-binding domains (chitinases, Jessie lectins, and Jacob lectins) and that the Jacob lectins are differentially modified by site-specific Cys proteases and O-phosphodiester-linked glycans.

* Corresponding author. Mailing address: Department of Molecular and Cell Biology, Boston University Goldman School of Dental Medicine, 715 Albany St., Evans 426, Boston, MA 02118. Phone: (617) 414-1054. Fax: (617) 414-1041. E-mail: jsamuels{at}bu.edu.

Eukaryotic Cell, May 2006, p. 836-848, Vol. 5, No. 5
1535-9778/06/$08.00+0     doi:10.1128/EC.5.5.836-848.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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Copyright © 2006 by the American Society for Microbiology.