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Eukaryotic Cell, October 2003, p. 1099-1114, Vol. 2, No. 5
1535-9778/03/$08.00+0     DOI: 10.1128/EC.2.5.1099-1114.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Posttranslational Modifications Required for Cell Surface Localization and Function of the Fungal Adhesin Aga1p{dagger}

Guohong Huang, Mingliang Zhang, and Scott E. Erdman*

Department of Biology, Syracuse University, Syracuse, New York 13244

Received 16 May 2003/ Accepted 7 August 2003

Adherence of fungal cells to host substrates and each other affects their access to nutrients, sexual conjugation, and survival in hosts. Adhesins are cell surface proteins that mediate these different cell adhesion interactions. In this study, we examine the in vivo functional requirements for specific posttranslational modifications to these proteins, including glycophosphatidylinositol (GPI) anchor addition and O-linked glycosylation. The processing of some fungal GPI anchors, creating links to cell wall ß-1,6 glucans, is postulated to facilitate postsecretory traffic of proteins to cell wall domains conducive to their functions. By studying the yeast sexual adhesin subunit Aga1p, we found that deletion of its signal sequence for GPI addition eliminated its activity, while deletions of different internal domains had various effects on function. Substitution of the Aga1p GPI signal domain with those of other GPI-anchored proteins, a single transmembrane domain, or a cysteine capable of forming a disulfide all produced functional adhesins. A portion of the cellular pool of Aga1p was determined to be cell wall resident. Aga1p and the {alpha}-agglutinin Ag{alpha}1p were shown to be under glycosylated in cells lacking the protein mannosyltransferase genes PMT1 and PMT2, with phenotypes manifested only in MAT{alpha} cells for single mutants but in both cell types when both genes are absent. We conclude that posttranslational modifications to Aga1p are necessary for its biogenesis and activity. Our studies also suggest that in addition to GPI-glucan linkages, other cell surface anchorage mechanisms, such as transmembrane domains or disulfides, may be employed by fungal species to localize adhesins.

* Corresponding author. Mailing address: Department of Biology, Syracuse University, 130 College Place, Syracuse, NY 13244. Phone: (315) 443-3748. Fax: (315) 443-2012. E-mail: seerdman{at}syr.edu. E-mail address for G. Huang: ghuang@syr.edu. E-mail address for M. Zhang: mlzhang{at}syr.edu.

{dagger} The supplemental material for this article may be found at http://ec.asm.org/

Eukaryotic Cell, October 2003, p. 1099-1114, Vol. 2, No. 5
1535-9778/03/$08.00+0     DOI: 10.1128/EC.2.5.1099-1114.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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