Download 슬라이드 1 - Korea University

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
 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
-J. Valle et al., “Broad-spectrum biofilm
inhibition by a secreted bacterial
polysaccharide,” PNAS 103(33): 1255812563. 2006.
 Medical and industrial relevance of fungal adhesion
1) The remarkable plasticity -> New drugs
2) Separate biomass from various fermentation products
• 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
Conclusion
• 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