Unraveling the yeast flocculation mechanism at the molecular level.

Francesco Ielasi, Katty Goossens, Livan Alonso, Sandor Kasas, Ronnie Willaert

Research output: Chapter in Book/Report/Conference proceedingMeeting abstract (Book)

Abstract

Yeast cell flocculation is exploited in the brewery industry as an easy, convenient and cost-effective way to separate the aggregated yeast cells from the beer at the end of the primary fermentation. The flocculation mechanism is based on a lectin-carbohydrate interaction but was until recently not yet fully understood, although the first model dates back to the 1950s. The Flo adhesin family is responsible for yeast cell flocculation. This family can be subdivided into two groups: (1) glycoproteins encoded by genes including FLO1, Lg-FLO1, FLO5 and FLO10, and (2) glycoproteins encoded by FLO11, FIG2 and AGA1. The first group of glycoproteins are lectins, and these proteins are responsible for the Ca2+-dependent flocculation phenotype.
A study of the flocculation mechanism on the molecular level, involving an ensemble of biotechnological and biophysical techniques, was carried on by our group. The N-terminal carbohydrate-binding domains of Flo1p from the ale yeast Saccharomyces cerevisiae and Lg-Flo1p from the lager yeast S. carlsbergensis were cloned, expressed and purified. Subsequently, a combination of X - ray protein crystallography and fluorescence spectroscopy allowed us to refine the model for the binding of these flocculins to yeast cell-wall glycans. In particular, X - ray protein crystal diffraction was used to solve the 3D structure of the flocculin domains in complex with calcium and mono- or oligosaccharides, while fluorescence titrations of protein solutions with carbohydrates helped to define binding specificities in a quantitative manner and also to determine influence of protein glycosylation on carbohydrate interactions. Finally, the use of Single-Molecule Force Spectroscopy (SMFS), as a further step in the biophysical characterization of flocculation molecules, produced interesting informations about the self-interaction forces of natively glycosylated Flo proteins in solution, both in favourable and unfavourable conditions for flocculation.
Original languageEnglish
Title of host publicationEBC Congress, Luxembourg.
Publication statusPublished - 20 May 2013
EventUnknown -
Duration: 20 May 2013 → …

Conference

ConferenceUnknown
Period20/05/13 → …

Keywords

  • beer
  • yeast
  • flocculation
  • Atomic Force Spectroscopy

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