enzymes part 2 proteases Flashcards
facts about protease
what types are they 4 types
serine cysteine aspartate metallo convergent evolution
triad enzymes
oxyanion hole what is it
special structure inside the enzyme to stabilise the transition state, acts by lowering the pKA of the oxianion
lessons from triad enzymes
the oxyanion negative charge develops twice, and there is a acyl enzyme intermediate
base usually histidine, taking a proton from nucleophile
increasing pKA
acid usually aspartate
changing substrate specificity
peptide nitrogens carry partial charge to compensate for oxyanion development during catalysis
trypsin cleaves peptide c-terminal to positively charged residues arg and lys
subtilisin cleaves peptides c-terminal to hydrophobic residues (phe, trp, tyr)
trypsin and subtilisin structure differences
no sequence homology
no structural homology
strong case of convergent evolution
same fold
protein target
need t be sorted into target compartments how
controlled by cleavage signal sequence
signal pepidases are ser proteases
serine protease have
high stability
low substrate specificity
in most laundry and dishwasher formulation
proteasome
protein degradation what is it dependent on
ubiquitin
requires ATP
proteasome structure
cap of 2x 19s
RPN: senses ubiquitination state
RPT: ATPase
central core 20s
what does the central core do
protease with large cavity, open at both sides
protease activity on the inside
what are proteolytically active
Beta 1 , 2 and 5
the catalytic ones
the proteosome
a threonine triad what is it and what does it do
its a threonine protease
the salt bridge lys33: asp17
which lowers the pKa of Thr1-0gamma
rhomboid proteases
where is it found
what does it do
found in membrane
cleave integral membrane proteins
important for maturation of proteins
they both have ser + his
Caspases: proteases of Death
what 2 processes are caused
Necrosis: unwanted cell death
apoptosis: controlled cell death
Caspases: proteases of Death
what happens
cystein protease leaves cys-asp
initiator: caspase 8,9
effector: caspase 3,7,9
chorea huntington
cystein protease
what is it
catalytic triad
with cystein as nucleophile
same as ser
unifying principle
nucleophilic attack at the carbonyl carbon
other triad differences
and eg
different chemical branch on each side of the amide or ester bond
beta-lactamase
peptidoglycans in bacteria
how is it synthesised
transpeptidases OH on ser attacks carbon substituting for alanine
then second chains amino group attacks the carbon where transpeptidase displacing transpeptidase
functions of penicilin
beta-lactam forms covalent enzyme adduct
this irreversibly inactivates the transpeptidase that synthesises peptidoglycans
function of beta lactamases
cleaves the beta lactam of penicilin
leading to antibiotic resistance
it is a triad enzyme
not reversible
second line antibiotics target
beta lactamase
clavulanic acid forms a covalent adduct that irreversibly inactivates the enzyme
aspartate protease
what happens
6 points
polarisation of water by general base attack on carbonyl C of the peptide formation of tetrahedral intermediate protonation of leaving group collapse of intermediate product leaves
