lab of industrial microbiology, korea university 2010010566 hyeon jeong eun

Lab of Industrial Microbiology, Korea university2010010566

Hyeon Jeong Eun

Introduction• Adhesion & Flocculation- One of the most critical functions of the cell surface- Prevents cells from being washed away- Allows them to form biofilms that offer protection ability

Fungal (Yeast) Adhesion 1) Adhere to abiotic surfaces such as plastic 2) Cell-Cell adhesion ( Flocculation )

=>Phenotypic variability and plasticity

Introduction

• Biofilm- A complex aggregation of microorganisms marked by the excretion of a protective and adhesive matrix

Medical and industrial relevance of fungal adhesion

1) The remarkable plasticity -> New drugs

2) Separate biomass from various fermentation products

-J. Valle et al., “Broad-spectrum biofilm inhibition by a secreted bacterial polysaccharide,” PNAS 103(33): 12558-12563. 2006.

• Adhesins or Flocculins ; Specialized cell-surface proteins

- Bind specific amino acid or sugar residues

A common three-domain structure

1) C-terminal : Glycosylphosphatidylinositol (GPI)-anchor

2) N-terminal : Carbohydrate or peptide binding domain

3) Middle domain

: Multiple serine and

threonine-rich repeats

• Fig1. Secretion and cell-surface anchoring of fungal adhesins

• FigS1. Phylogenetic tree of cellular adhesins and mucins

• Fig2. Cell-cell and cell-surface adhesion associated with the S. cerevisiae FLO genes

[1] Expresses the FLO1

[2] Does not express any FLO gene

[3] Overexpresses FLO11

• Different of mechanisms of adhesion

1) Lectin-like adhesion (sugar sensitive)• N-terminus : lectin-like carbohydrate binding domain• Two sub-categories - Flo1 group : only binds mannose sugars - NewFlo group : binds various sugars

2) Sugar-insensitive adhesion• bind peptides or increase the cell-surface hydrophobicity

• Controlled by several signaling pathways- Triggered by certain stress factors and/or nutrient limitation

FLO11-mediated cell-surface adhesion 1) Ras-cAMP pathway 2) MAP kinase-dependent filamentous growth pathway 3) The main glucose repression pathway

( not yet known ) 4) Target of Rapamycin (TOR) pathway – nitrogen starvation 5) Transcription factors Sok2, Phd1, Adh1 – Epistatic pathway

• Fig3A. The MAPK-dependent filamentous growth pathway

Ste11, Ste7: Central kinase

Msb2 : mucin-like transmembrane protein

Mep2: Ammonium permease

• Fig3B. The Ras/cAMP/PKA pathway

Cyr1: adenylate cyclase

PKA: Protein kinase A complex

Sfl1: Suppressor of flocculation

• Fig3B. The main glucose repression pathway

Hxt: Hexose transporters

Hxk: Hexokinases

Sfl1: Suppressor of flocculation

• Controlled epigenetically

1) Cells regulary switch between the states ( transcribed <-> silent )

2) Stochastic switching mechanism ( Nonsense mutation )

3) Chromatin remodeling

Goals of adhesins silencing

1) Balance between adhering, colonizing cells and non-adhering cells

2) Proactively anticipate new conditions in fluctuating environments

3) Allowing them to adhere to specific surfaces only

4) Different subsets may allow evasion of the host immune system

• Recombination of Intragenic repeats ; Novel adhesins

- Fastest expanding group of paralogues in the genomes

The driving force behind the creation of novel adhesins

1) Trigger frequent slippage, recombination events - Longer adhesins generally confer greater adherence

2) Recombination events between repeats of different genes - Generate chimeirc forms

• Fig4. Box plot of the S. cerevisiae FLO1 nucleotide sequence

• Fungal adhesion is an unusually complex and variable phenotype

1) Quickly adapt their adhesive properties to a particular environments

2) Many different genetic and epigenetic signaling cascades

3) The internal tandem repeats trigger frequent recombination events

• For Industrial applications,

the instability of the flocculation profile is a true nightmare

Recombinant DNA techniques

• For Medical applications,

the remarkable plasticity of fungal adhesion also causes concern

Targets for new drugs

Conclusion