Tandem Repeats Domain in Candida Albicans Als Adhesins

Abstract

Yeast adhesins are involved in binding interactions to other cells, substrates and surfaces. Als adhesins in Candida albicans consists of 8 homologous proteins. The proteins are composed of an N terminal signal sequence, three Ig-like domains, a threonine rich (T) region, tandem repeats (TR), a glycosylated stalk and C-terminal GPI-anchor to the cell wall. Tandem repeats in the C. albicans Als adhesins consist of 2 to 36 copies of a 36-residue sequence.Tandem repeat domain structures from six Als adhesins were modeled by Rosetta and LINUS. Both methods produced a three-stranded antiparallel β-sheet. This is consistent with circular dichroism (CD) secondary structure and atomic force microscopy domain measurements. Models of glycosylated TR domains show carbohydrates surrounding hydrophobic patches. This is the basis of protein-protein and protein-substrate interactions. In addition, the presence of tandem repeats led to enhanced non-saturable binding to polystyrene and other TR domains. Interestingly, TR domains do not affect the isosbestic point in thermal CD experiments.This modeling structure and function of the tandem repeats in Als proteins can be applied to repeat regions in other yeast adhesins proteins.