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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 
-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.
Published ahead of print on 25 August 2006.
Present
address: Dept. of Microbiology, Columbia University College of Physicians and Surgeons, New York, NY 10032.
This article has been cited by other articles:
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