Molecular interactions between hosts and pathogens

Partho GhoshDepartment of Chemistry & Biochemistry

and Section of Molecular BiologyUniversity of California, San Diego

http://pghosh.ucsd.edu

Pathogens Host cells

VirulenceFactors

Host Cell Target

Establishment of niche in hostSubversion of host defenses and immunityProliferation in hostTransmission to other hosts

Infectious Diseases at the Molecular Level

Type III Secretion Needles

Kubori et al., Science 280:602 (98)

Pathogenic bacterium

Human cell

Type III Secretion System (TTSS)• Gram-negative

• Pathogens of mammals–Escherichia coli –Pseudomonas aeruginosa–Salmonella tymphimurium–Shigella flexneri–Bordetella pertussis–Chlamydia trachomatis–Yersinia spp.

• Pathogens of plants–Erwinia amylovora–Pseudomonas syringae–Ralstonia solanacearum–Xanthomonas campestris

Pseudomonas aeruginosa• Ubiquitous and antibiotic-resistant bacterium

• Problem for patients with weakened immune systems

• Certain strains cause severe and acute infections

• 90% of severe and acute strains— inject the protein ExoU into human cells, results in cell death

CDC

Phospholipase A2 motifs — destroy mammalian cell membranes

But, overall identity to phospholipase ~10%

How does ExoU function?Using genome sequences to get

the answer

Phillips et al. JBC (03)

Testing the phospholipase idea: Syringe Loading

Clarke & McNeil. (1992) J Cell Sci 102:533-41

106 mammalian cells+

ExoU

?

ExoU kills mammalian cells and needs sites 1 and 2

Cel

l Dea

th

ExoU

Site 1

Site 2

ExoU needs a mammalian cell component

ExoU-GFP

Learning what that component is using yeast

Yeast making ExoU

Yeast without ExoU

ExoU kills cells but

Phospholipase inhibitors block

cell death

Cel

l Dea

th

Inhibitors

Will inhibitors stop Pseudomonas?

Pseudomonas aeruginosa+ inhibitor

Inhibitors protect against Pseudomonas

Cel

l Dea

th

Pseudom

onas

w/o E

xoU

Pseudom

onas

+ Inhib

itor

Pseudom

onas

CurrentAnn CaiAlicia GamezJyothi KumaranCase McNamaraJason MillerRebecca PhillipsCatarina RaposoLoren Rodgers

UCSDEd DennisDavid Six

Lorraine Pillus

William Fenical

University of TorontoCharlie Boone

FundingW.M. Keck FoundationCystic Fibrosis Foundation