LYSOZYME LYSOZYME MECHANISM OF MECHANISM OF ACTION ACTION D.YESHWANTH KUMAR (1 st YEAR M.TECH BIOTECHNOLOGY)
LYSOZYMELYSOZYMEMECHANISM OF MECHANISM OF
ACTIONACTION
D.YESHWANTH KUMAR(1st YEAR M.TECH BIOTECHNOLOGY)
INTRODUCTIONINTRODUCTIONNatural Anti-bacterial agent
129 amino acid residues
Molecular Mass – 14.3 kD (hen egg lysozyme)
Found at: egg whites and tears
Substrate: Peptidoglycan
3-D Structure: Determined by David Phillips, et al. in 1965
SUBSTRATE: PEPTIDOGLYCANSUBSTRATE: PEPTIDOGLYCAN
Site of cleavage
• It’s a Carbohydrate• NAM: N-acetylmuramic Acid• NAG: N-acetylglucosomine• Cleaves NAM-NAG site at β(1→4)
glycosidic C–O bond• NAM contains lactyl (lactic acid)
group side Chain which forms the peptide bridge
STRUCTURE OF LYSOZYME (RIBBON DIAGRAM)
•The Blue sticks are Glu35 and Asp52 (active site)
•The red sticks are the substrate (peptidoglycan)
LYSOZYME + SUBSTRATE LYSOZYME + SUBSTRATE REACTIONREACTION
KEY
• RO: Lactyl group
• NAc/AcN: N-acetyl group
LYSOZYME: MECHANISM OF LYSOZYME: MECHANISM OF ACTION (SACTION (SNN1 MECHANISM)1 MECHANISM)
Peptidoglycan binds to the active site of the lysozyme
This reaction is a nucleophilic displacement reaction
Half life of the intermediate 10-12 secnds
Acid Catalysis
Highly Unstable
LYSOZYME: MECHANISM OF LYSOZYME: MECHANISM OF ACTION (SACTION (SNN1 MECHANISM)1 MECHANISM)
Proposed in 1965
This mechanism accepted for around 3 decades
Reasons for Failure:
Experimentally not proved and satisfactory
Lysozyme catalyzes the reaction where highly unstable intermediates are being formed
LYSOZYME: MECHANISM OF LYSOZYME: MECHANISM OF ACTION (SACTION (SNN2 MECHANISM)2 MECHANISM)
Involves two consecutive direct displacement steps
Acid catalysis addressed as in first step
More stable covalent intermediate was formed
This also involves nucleophilic displacement reaction
Acid Catalysis
Covalent Catalysis
LYSOZYME: MECHANISM OF LYSOZYME: MECHANISM OF ACTION (SACTION (SNN2 MECHANISM)2 MECHANISM)
Proposed in 2001
Proven by Stephen Withers, et al.
Experimentally proven
Formation of more stable covalent intermediate (covalent catalysis)