Eukaryotic Cell
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Eukaryotic Cell, October 2006, p. 1664-1673, Vol. 5, No. 10
1535-9778/06/$08.00+0     doi:10.1128/EC.00120-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Threonine-Rich Repeats Increase Fibronectin Binding in the Candida albicans Adhesin Als5p{triangledown}

Jason M. Rauceo,1,{dagger} Richard De Armond,2 Henry Otoo,1 Peter C. Kahn,3 Stephen A. Klotz,4 Nand K. Gaur,2 and Peter N. Lipke1*

Department of Biology and the Center for Gene Structure and Function, Hunter College of the City University of New York, New York, New York,1 Southern Arizona VA Health Care System, Tucson, Arizona,2 Department of Biochemistry and Microbiology, Cook College Rutgers University, New Brunswick, New Jersey,3 Department of Medicine, University of Arizona, Tucson, Arizona4

Received 20 April 2006/ Accepted 10 August 2006

Commensal and pathogenic states of Candida albicans depend on cell surface-expressed adhesins, including those of the Als family. Mature Als proteins consist of a 300-residue N-terminal region predicted to have an immunoglobulin (Ig)-like fold, a 104-residue conserved Thr-rich region (T), a central domain of a variable number of tandem repeats (TR) of a 36-residue Thr-rich sequence, and a heavily glycosylated C-terminal Ser/Thr-rich stalk region, also of variable length (N. K. Gaur and S. A. Klotz, Infect. Immun. 65: 5289-5294, 1997). Domain deletions in ALS5 were expressed in Saccharomyces cerevisiae to excrete soluble protein and for surface display. Far UV circular dichroism indicated that soluble Ig-T showed a single negative peak at 212 nm, consistent with previous data indicating that this region has high ß-sheet content with very little {alpha}-helix. A truncation of Als5p with six tandem repeats (Ig-T-TR6) gave spectra with additional negative ellipticity at 200 nm and, at 227 to 240 nm, spectra characteristic of a structure with a similar fraction of ß-sheet but with additional structural elements as well. Soluble Als5p Ig-T and Ig-T-TR6 fragments bound to fibronectin in vitro, but the inclusion of the TR region substantially increased affinity. Cellular adhesion assays with S. cerevisiae showed that the Ig-T domain mediated adherence to fibronectin and that TR repeats greatly increased cell-to-cell aggregation. Thus, the TR region of Als5p modulated the structure of the Ig-T region, augmented cell adhesion activity through increased binding to mammalian ligands, and simultaneously promoted fungal cell-cell interactions.


* Corresponding author. Present address: Dept. of Biology, Brooklyn College, 2900 Bedford Ave., Brooklyn, NY 11210. Phone: (718) 951-5000, ext. 1949. Fax: (718) 951-4659. E-mail: lipke{at}genectr.hunter.cuny.edu.

{triangledown} Published ahead of print on 25 August 2006.

{dagger} Present address: Dept. of Microbiology, Columbia University College of Physicians and Surgeons, New York, NY 10032.


Eukaryotic Cell, October 2006, p. 1664-1673, Vol. 5, No. 10
1535-9778/06/$08.00+0     doi:10.1128/EC.00120-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.




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