Interactions by the Fungal Flo11 Adhesin Depend on a Fibronectin Type III-like Adhesin Domain Girdled by Aromatic Bands

Abstract

Saccharomyces cerevisiae harbors a family of GPI-anchored cell wall proteins for interaction with its environment. The flocculin Flo11, a major representative of these fungal adhesins, confers formation of different types of multicellular structures such as biofilms, flors, or filaments. To understand these environment-dependent growth phenotypes on a molecular level, we solved the crystal structure of the N-terminal Flo11A domain at 0.89-Å resolution. Besides a hydrophobic apical region, the Flo11A domain consists of a β sandwich of the fibronectin type III domain (FN3). We further show that homophilic Flo11-Flo11 interactions and heterophilic Flo11-plastic interactions solely depend on the Flo11A domain and are strongly pH dependent. These functions of Flo11A involve an apical region with its surface-exposed aromatic band, which is accompanied by acidic stretches. Together with electron microscopic reconstructions of yeast cell-cell contact sites, our data suggest that Flo11 acts as a spacer-like, pH-sensitive adhesin that resembles a membrane-tethered hydrophobin.

Clonal yeast biofilms can reap competitive advantages through cell differentiation without being obligatorily multicellular

“…Flocculation protects S. cerevisiae cells from environmental stress [19] but does not provide a novel and potentially synergistic growth form as the FLO11 biofilm phenotype does. Flocculation relies on the production of Flo proteins with a PA4 domain, such as Flo1p, Flo5p, Flo9p and Flo10p that form Ca 2þ -dependent heterophilic interactions with mannose residues on the cell walls to adhere to neighbouring cells [24], whereas the biofilm phenotype of our present study relies on homophilic protein (Flo11p-Flo11p) interactions [25]. Finally, the organization of S. cerevisiae biofilms is also clearly different from any form of filamentous multicellularity such as found in Streptomyces [39], where clonal cell differentiation has evolved to enhance spore dispersal rather than resource acquisition.…”

Gravity-Driven Adaptive Evolution of an Industrial Brewer’s Yeast Strain towards a Snowflake Phenotype in a 3D-Printed Mini Tower Fermentor

“…The population at the start, and after seven and fifteen days were compared ( Figure 5). The CMBSVM22 strain possesses the FLO11 gene required for invasive growth [32,[47][48][49], which could clearly be seen on the bottom of the plates. The morphology of the colonies differed after 14 days, the same time when the snowflake flocs were observed.…”

Biofilm formation and toxin production provide a fitness advantage in mixed colonies of environmental yeast isolates

“…While the assay was performed in an artificial laboratory setting, the results suggest that increased use of space by yeast biofilms may not only provide an escape from competition for nutrients, but may also provide an escape from warfare phenotypes. It is interesting to note that the toxin and Flo11p, the cellular adhesin responsible for cell–cell attachment, are both most effective in acidic conditions (Kraushaar et al., 2015; Lukša et al., 2016); we thus speculate that yeast biofilms and toxins could interact in the natural environment.…”

“…A spatially explicit cooperative yeast phenotype is complex colony morphology (“fluffy”), which resembles the wrinkly colonies of the bacterial biofilm models P. aeruginosa and Bacillus subtilis , and has all the hallmarks of fungal biofilms (Blankenship & Mitchell, 2006): An extracellular matrix facilitating nutrient flow and water retention (Kuthan et al., 2003; Štovíček, Váchová, Kuthan, & Palková, 2010); expression of drug efflux pumps; and velcro‐like structures attaching cells to one another (Váchová et al., 2011) encoded by an adhesin gene, FLO11 (Kraushaar et al., 2015). When grown as single‐strain colonies (Tan et al., 2013) or mats (Regenberg, Hanghøj, Andersen, & Boomsma, 2016), strains forming biofilms have been shown to spread and occupy space more quickly than non‐biofilm‐forming (smooth) strains; however, smooth colonies have a greater cell density (Štovíček et al., 2010).…”