title: Threonine-rich repeats increase fibronectin binding in the Candida albicans adhesin Als5p.
abstract: 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 beta-sheet content with very little alpha-helix. A truncation of Als5p with six tandem repeats (Ig-T-TR(6)) 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 beta-sheet but with additional structural elements as well. Soluble Als5p Ig-T and Ig-T-TR(6) 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.
authors.affiliation: Dept. of Biology, Brooklyn College, 2900 Bedford Ave., Brooklyn, NY 11210, USA.
authors.forename: Jason M
authors.initials: JM
authors.lastname: Rauceo
authors.forename: Richard
authors.initials: R
authors.lastname: De Armond
authors.forename: Henry
authors.initials: H
authors.lastname: Otoo
authors.forename: Peter C
authors.initials: PC
authors.lastname: Kahn
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Klotz
authors.forename: Nand K
authors.initials: NK
authors.lastname: Gaur
authors.forename: Peter N
authors.initials: PN
authors.lastname: Lipke
mesh_terms: D000818:Animals; D002176:Candida albicans / Q000378:metabolism*; D002448:Cell Adhesion; D015815:Cell Adhesion Molecules / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D002942:Circular Dichroism; D003208:Concanavalin A / Q000378:metabolism; D005353:Fibronectins / Q000378:metabolism*; D005656:Fungal Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D006735:Horseradish Peroxidase / Q000378:metabolism; D007136:Immunoglobulins / Q000302:isolation & purification; D010446:Peptide Fragments / Q000378:metabolism; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D020449:Repetitive Sequences, Amino Acid; D013379:Substrate Specificity; D013912:Threonine / Q000737:chemistry*; D015003:Yeasts / Q000166:cytology
chemical_list: C109455:ALA1 protein, Candida albicans; D015815:Cell Adhesion Molecules; D005353:Fibronectins; D005656:Fungal Proteins; D007136:Immunoglobulins; D010446:Peptide Fragments; D003208:Concanavalin A; D013912:Threonine; D006735:Horseradish Peroxidase