lab of industrial microbiology, korea university 2010010566 hyeon jeong eun
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Lab of Industrial Microbiology, Korea university 2010010566 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. - PowerPoint PPT PresentationTRANSCRIPT
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