The dual role of amyloid-β-sheet sequences in the cell surface properties of FLO11-encoded flocculins in Saccharomyces cerevisiae.

Clara Bouyx,Marion Schiavone,Nathalie Sieczkowski,Marie-Ange Teste,Anne Julien,Etienne Dague,Jean Marie François

doi:10.7554/elife.68592

Abstract

Fungal adhesins (Als) or flocculins are family of cell surface proteins that mediate adhesion to diverse biotic and abiotic surfaces. A striking characteristic of Als proteins originally identified in the pathogenic Candida albicans is to form functional amyloids that mediate cis-interaction leading to the formation of adhesin nanodomains and trans-interaction between amyloid sequences of opposing cells. In this report, we show that flocculins encoded by FLO11 in Saccharomyces cerevisiae behave like adhesins in C. albicans. To do so, we show that the formation of nanodomains under an external physical force requires a threshold number of amyloid-forming sequences in the Flo11 protein. Then, using a genome editing approach, we constructed strains expressing variants of the Flo11 protein under the endogenous FLO11 promoter, leading to the demonstration that the loss of amyloid-forming sequences strongly reduces cell-cell interaction but has no effect on either plastic adherence or invasive growth in agar, both phenotypes being dependent on the N- and C-terminal ends of Flo11p. Finally, we show that the location of Flo11 is not altered either by the absence of amyloid-forming sequences or by the removal of the N- or C-terminus of the protein.

Highlights

The yeast cell wall is a highly dynamic structure that is an armour separating cell from its surrounding but that is endowed of surface properties including adherence to inert material leading to biofilm formation, cell-c ell adhesion that can yield to flocculation, hydrophobicity which may result in buoyant biofilms
The presence of abundant patches at the cell surface of a wine yeast L69 strain under the contact of an atomic force microscopy (AFM) bare tip described in a previous work (Schiavone et al, 2015), which were totally absent on the surface of the laboratory strain BY4741 (Figure 1—figure supplement 1), prompted us to examine in detail the physical properties of these nanosized patches using AFM in quantitative imaging (QI) mode as this technique enables to image at high resolution and to quantify adhesive properties of the cell surface (Chopinet et al, 2013)
This AFM analysis showed that the nanoscale spots on the cell surface of strain L69 exhibit nanomechanical characteristics very similar to those of adhesin nanodomains in C. albicans (Alsteens et al, 2010; Formosa et al, 2015b), and raised the question of whether a same cell wall component is responsible for formation of these patches, as it is the case in C. albicans

Summary

Introduction

The yeast cell wall is a highly dynamic structure that is an armour separating cell from its surrounding but that is endowed of surface properties including adherence to inert material leading to biofilm formation, cell-c ell adhesion that can yield to flocculation, hydrophobicity which may result in buoyant biofilms. This 3D organization of adhesins into nanodomains has been shown to be triggered by an external physical shear force, such as the extension force of single molecules stretched by an atomic force microscopy (AFM) tip, which propagates across the cell surface at a speed of about 20 nm/min (Alsteens et al, 2010) This unique phenomenon was explained by the presence of small amyloid-c ore sequences of five to seven residues (IVIVATT) in adhesin proteins that are characterized by a high content of β-branched aliphatic Ile, Val, and Thr forming β-aggregates structures as predicted by the β-aggregate predictor TANGO (Fernandez-Escamilla et al, 2004b; Lipke et al, 2018). The formation of these nanodomains is an emergent property of adhesin primary sequence that promotes cell-cell aggregation, resulting in the formation of

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