Eukaryotic Cell doi:10.1128/EC.00120-06
Copyright (c) 2006, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.
Threonine-rich repeats increase fibronectin binding in the C. albicans adhesin Als5p
Jason M. Rauceo,
Richard DeArmond,
Henry Otoo,
Peter C. Kahn,
Stephen A. Klotz,
Nand K. Gaur,
and
Peter N. Lipke*
Dept. of Biology and the Center for Gene Structure and Function, Hunter College of the City University of New York, New York, NY, Southern Arizona VA Health Care System, Tucson, AZ, Dept. of Biochemistry and Microbiology, Cook College Rutgers U., New Brunswick, NJ, Dept. Medicine, U. Arizona, Tucson, AZ.
* To whom correspondence should be addressed. Email:
lipke{at}genectr.hunter.cuny.edu.
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Abstract |
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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-like fold (Ig), 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 (Gaur, N.K and S.A. Klotz, 1997. Infect. Immun. 65:5289-94). Domain deletions in ALS5 were expressed in S. 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 that this region has high 
-sheet content with very little 
-helix. A truncation of Als5p with six tandem repeats (Ig-T-TR6) gave spectra with additional negative ellipticity at 200 nm and at 227-240 nm, characteristic of a structure with a similar fraction of -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 in 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.
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