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Name three Serine Proteases; where are they found?
- Elastase, Chemotrypsin, Trypsin
- In the pancreas
What residues types do Elastase, Chemotrypsin and Trypsin target?
- Trypsin - Small, positive residues
- Chemotrypsin - Bulky hydrophobes
- Elastase - Small nonpolar residues
What is the basic structure of the three key Serine Proteases?
- Two domains
- - i.e two 6 stranded antiparallel β-barrels
What are the three key residue locations in the specificity pocket?
226, 189, 216
What two proteases contain Gly 226 and Gly 216?
Trypsin (Aspartate 189) and Chemotrypsin (serine 189)
What three residues does Elastase have in it's specificity pocket?
Valine 226, Threonine 216 and nothing at the 189 position
What are the three residues of the catalytic triad?
Aspartate (102), Histidine (57) and Serine (195)
What does BPTI stand for?
Bovine Pancreatic Trypsin Inhibitor
How does BPTI act?
Binds very tightly to Trypsin in transition state conformation
Why is BPTI not cleaved in trypsin?
- The leaving group is trapped
- -> Evidence of tetrahedral transition
What redisues make up the Oxyanion hole?
Serine 195 and Glycine 193
Why is the oxyanion hole important?
- It provides a stable "resting spot" for the carbonyl oxygen in the tetrahedral transition state
- Basically, it stabillizes the transition state by hydrogen bonding)
What happens if you mutate the catalytic triad? Why is this so?
Enzymatic activity is reduced, but still significant. This is because catalysis relies heavily on transition state binding, as well as traditional catalytic mechanisms
What is a zymogen?
Inactive proteolytic enzyme precursor
Why is nascent trypsin inactive?
Specificity pocket and oxyanion hole are improperly formed
Do serine proteases in different organisms have the same or similar residues?