PROSITE documentation PDOC51824

Flocculin 11 (Flo11) domain profile

Fungal cells need to be able to adhere to their surroundings, be it either abiotic surfaces or living tissues, in order to remain firmly attached to their source of nutrients. Adhesive properties in fungi are conveyed by a group of cell-surface proteins called adhesins (sometimes also referred to as agglutinins or flocculins). Adhesins are generally rich in serine and threonine residues that allow extensive O-linked glycosylation. Some fungal adhesins also carry discernable ligand-binding domains that determine their substrate specificity and allows some degree of sequence classification of the different groups of adhesins. Flocculin 11 is the major adhesin for controlling filamentous growth, mat, and biofilm formation of bakers's yeast. Although its amino acid sequence shows less similarity with the other flocculins, Flo11 belongs to the flocculin family. However, the N-terminal domain contains the 'Flo11 domain', but not the mannose-binding PA14 domain (see <PDOC51820>), which is present in most other flocculins (Flo1, Flo5, Flo9 and Flo10). Flo11 domains are only found within the ascomycetal orders of Saccharomycetales, which include the budding yeasts as well as the Schizosaccharomycetales, i.e. the fission yeast Schizosaccharomyces pombe. In the majority of its family members, the Flo11 domain is located at the N-terminal ends of glycosylphosphatidylinositol (GPI)-anchored cell wall proteins, although some yeasts such as Clavispora lusitaniae or Spathaspora passalidarum have arrays of up to three Flo11 domains within their adhesins. The Flo11 domain is not a mannose-binding module but can make homotypic interactions [1,2,3].

The Flo11 domain consists of some 160 amino acids. It is O-glycosylated and is structurally composed mainly of β-sheets, which is typical for the members of the flocculin family. The Flo11 domain structure corresponds to a globular, wedge-shaped domain with a complex folding motif that consists of three anti-parallel β sheets (see <PDB:4UYR>). The sheets I and II form a β sandwich as core domain, whereas the four-pleated sheet III forms a unique, neck-like subdomain along the lower end of the β sandwich. The core domain, namely the β-sandwich formed by the anti-parallel β sheets I and II, was assigned to the class of fibronectin type III-like domains (FN3) (see <PDOC50853>) [3].

The profile we developed covers the entire Flo11 domain.