Serine proteases

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8 Terms

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What class of enzymes are serine proteases?

Hydrolases, proteases(peptidases)

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How do sereine proteases speed up reactions?

  • Covalent catalysis

  • Gen acid/base catalysis

  • Intermediate/transition state stabilization

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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

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Catalytic triad

  • His 57- gen acid/base

  • Ser 195- nucleophile

  • Asp 102- modulation of his 57

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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

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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

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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)

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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_