Cullen Lecture 6:Signal Transduction in

Fungi

Filamentous GrowthFilamentous Growth

Saccharomyces cerevisiae (G . Fink)And fungal pathogens

Specificity of Signaling Pathways Containing

Cdc42and MAPK Components

in Yeast

Signal Transduction Pathways Control Fungal Behavior

Stimulus Response New Cell TypeSignaling

Cell

Nucleus

Receptor

FGP

?

Cdc42/Ste20

Ste11Ste7Kss1

Ste12/Tec1

Filamentous Growth Pathway

Receptor:

GTPase/PAK:

MAPK3:MAPK2:MAPK:

Txn1/Txn2:

Yeast Signaling Proteins are Homologous to Mammalian

Counterparts

http://www.hhmi.org/research/investigators/wu.html

“Cross-Talk” in Signaling Pathways

Prediction of Specificity Factors

Sho1Ste2042

??

Cell Wall

Membrane

FGP

Sho1 + ?

Cdc42/Ste20

Ste11Ste7Kss1

Ste12/Tec1

Characterize the Msb2 Protein

Msb2 is glycosylated

Msb2 is an Integral Membrane Protein

Msb2

Topology of Msb2

Cell Wall

Plasma Membrane

Glycosylated

Integral Membrane

Cell Surface

Ste2042

Msb2

Sho1

Topology and Domain Structure of Msb2

Mucin-HomologyDomain

SignalSequence

Membrane-SpanningDomain

100 AA

Extracellular Cytoplasmic

Glycosylation Sites

Msb2

Msb2 is a Mucin

Cell Wall

Plasma Membrane

Mucin-HomologyDomain

Mucins are Gross but Important

Mucins in Mammalian Cells

Disease resistance

Metastasis

Signaling role

MUC1 and MUC4

Docks ß-cateninGrb2-Sos-Ras-MEK-ERK2 pathway

Erb2/Her2/NeuErb2-Erb3

Msb2’s Mucin-Homology Domain

100 AA

N…(698)S Q V S D T SV S Y T T S S S S V S Q V S D T PV S Y T T S S S S V S Q V S D T PV S Y T T S S S S V S Q V S D T PV S Y T T S S S S V S Q V S D T PV S Y T T S S S S V S Q V S D T SV P S T S S S S S V S Q V S D T PV P S T S S S S S V S Q (818) …C

wt mucin

Msb2 w/o the Mucin Domain is Hyperactive

Is the Mucin Domain Required for FG Pathway Activity?

Mucin Repeats Are Inhibitory

Repeats are Homologous at the Nucleotide Level

Undergo Recombination-Mediated Deletion

Analysis of the Mucin Repeats (Continued)

Msb2-Dependence of MAPK Specificity

PRP

Receptor

Fus3

FGP

Msb2

Kss1

Msb2 induces Kss1~P but not Fus3~P

Msb2 induces Kss1~P but not Fus3~P

Conclusions

Msb2 is a glycosylated integral-membrane cell-surface signaling mucin at the head of the

FG pathway

Msb2 is a FG pathway specific factor and part of the presumptive sensory complex

Cdc42 and Sho1 are recruited to the FG pathway by Msb2

The mucin domain of Msb2 inhibits its function

Msb2 is Secreted by the Exocyst Complex