mutational analysis of the enzymatic domain of clostridium difficile toxin b reveals novel...
TRANSCRIPT
Mutational Analysis of the Enzymatic Domain of Clostridium
difficile Toxin B Reveals Novel Inhibitors of the Wild-Type Toxin
Authors: Lea M. Spyres, Jeremy Daniel, Amy Hensley, Maen Qa’Dan, William Ortiz-Leduc,
and Jimmy D, Ballard
Presented by: S. Camphor
Background
• Clostridium difficile (C.difficile) -gram positive
-anaerobic-spore former-major cause of hospital acquired diarrhea& Pseudomembranous colitis-some cases colitis is life-threatening
Background ….
• What is pseudomembranous colitis?
-severe irritation of the colon
-caused by C.difficile when the normal flora of the gut is wiped out due to antibiotic use
-illness characteristics
1. diarrhea
2. fever
3. abdominal cramping/pain
Background continued…..Statistics (U.S.)
C. difficile• Found that:
-20% of hospitalized patients suffer (about 3 million cases/year)
-30% of these develop diarrhea• Asymptomatic:
-2%-3% of healthy adults -70% of healthy infants and youth-low mortality/morbidity rate
(10%-30% of seriously ill will die)
Introduction….
• Current treatment:
-Antibiotics ( could this perpetuate the problem?)
-supportive therapy• New treatments:
-Tx with Saccharomyeces boulardii
• Future treatments:
-therapeutics that target major virulent factors to prevent major cell specific cytoxic activities.
Intro continued…….
• Toxins A & B-LCTs (Large clostridial toxins)-involved in development of colitis-toxin A enterotoxin
• Toxin B (cytotoxin)-glucosylates isoforms of Rho, Rac, and Cdc 42.-structures:- enzymatic
- translocation - receptor binding domains
-triggers caspase-dependent / independent apoptosis
Intro continued…..
• Tcd B enzymatic domain focus:
-activity requires all 546 amino terminal amino acids
-if deletion in amino or carboxy terminal a reduction in activity is seen
Toxin B as a target for drug therapy?
• Toxin B
- possible drug therapy through activity inhibition
- Paper: investigates use of mutants to block CPEs (cytopathic effects)
Materials and Methods…• Created fusion proteins using lfn ( encodes
Ag binding region of anthrax toxin lethal factor)
- 4 with deletions
- 3 site-directed mutations
(mutations and deletions in enzymatic domain)• Fusion proteins used in various assays to
determine inhibition capabilities of Tcd B.
Figure 1 A/B: A: deletion and site-directed mutants used in studyB: SDS-PAGE analysis of histone fused tags.
Results:
Lfn- used for mutants to gain entry into the cell.
Table 1:Glucosylhydrolase activity using UDP-glucose as a substrate to determine if defective hydrolase activity was the reason for inability for target modification
Figure 2 A/B Glucosylation activity of Mutants
A: SDS-PAGE of each mutant and TcdB glucosylation acitivity on RhoA, Rac1 and Cdc 42B: LFnTcdB 1-500 test to see if deletion mutant attenuated modification of substrate
Results …..
Figure 3A: actin condensation and cell rounding in the inhibitor assay.
Figure 3B: Summary of inhibitors capable of blocking TcdB CPEs. - Antagonistic impact on Toxin B intoxication - Inhibition decrease over time
Legend:
Solid: LFnTcdB1-420
Open: LFnTcdB w102A
Dotted: LFnTcdB c365w
Checkered: LFnTcdB 33-556
Hatched: LFn TcdB1-500
Figure 4:
Monitoring of CPEs. Are the inhibitory effects really limited?
- more than 50% of cells show no sign of CPEs.
Figure 5:Is inhibition occurring in the cytosol?Use CHO cell line that induce expression of TcdB1-556
Eventually presence of CPEs because of cells continuous production of TcdB1-556
Figure 6: Is inhibition due to competition for substrate or co-substrate?
-TcdB1-500 added to see if protection from TcsL
-Both TcsL and TcdB share Rac as a common substrate.
almost 50% block of TcsL
Discussion
• Mutants
-don’t modify substrate
-have cytosolic functions that allow inhibition
Question:
-Is the inhibition occurring because of prevented access of UDP-glucose to toxin B?
Discussion…
• TcsL assay
-show inhibition at cosubstrate level b/c only Rac in common with Toxin B
-effects would be less effective on TcsL if Rho, Rac and Cdc42 involved
-inhibition at the co-substrate level because no effect seen with Tcnα
Future use…
• This study provides possibility of useful therapeutic treatments in the future, targeting toxin B.
• Cell surface studies to better understand the surface interacting regions
• More studies on inactive mutants in other viruses