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What class of enzymes are serine proteases?
Hydrolases, proteases(peptidases)
How do sereine proteases speed up reactions?
Covalent catalysis
Gen acid/base catalysis
Intermediate/transition state stabilization
Structure of serine proteases
Around 240 a.a long
Synthesized as zymogens-cleavage of peptide chain activates
2 domains (B-barrel) with active site at junction
Extracellular (digestive)- disulphide bonds
Specificity pocket
Catalytic triad
Catalytic triad
His 57- gen acid/base
Ser 195- nucleophile
Asp 102- modulation of his 57
Catalytic residues
His 57- gen acid/base
Ser 195- nucleophile
Asp 102- modulation of his 57
Oxydation hole: gly 193, ser 195
Asp 194+ Ile 16(NH3+) - zymogen activation
Specificity
Specificity pocket determines what will bind their=what lines up with active site
Chymotrypsin- cleaves peptides after large hydrophobic residues
Trypsin- after positively charged residues
Elastase- after small non-polar residues
Oxyanion hole
Backbone NH groups of 193/195, partially positive- h-bond interactions with - oxygen that forms
Ideal interaction when the carbonyl carbon of the peptide bond being cleaved is tetrahedral (not planar)
Chymotrypsin mechanism
General acid base (Asp102, His57Gen base) to tetrahedral intermediate (N as leaving)
Gen acid base (His57-acid, Ser195) to acrylic-enzyme intermediate
What was C terminal becomes new N terminal
Amine product is released and replaced by water
Gen base catalysis (His57) and nucleophilic attack to form tetrahedral intermediate
Gen acid catalysis (his 57) to breakdown tetrahedral intermediate to carboxyl product and active enzyme
New C-terminus (N portion of initial_