Lysozymes Flashcards
What does lysozyme contribute to the structure of peptidoglycan?
Antibacterial properties: Hydrolyses the polysaccharide component of peptidoglycan
Define peptidoglycan
Complex polymer found in bacterial cell walls
What do polysaccharides contribute to the structure of peptidoglycan?
Polysaccharides in peptidoglycan have a disaccharide repeat structure
Polysaccharides: Explain the disaccharide repeat structure
Formed by Beta1 -> 4 linked glycosidic bonds between N-acetyl-muramic acid (NAM) and N-acetyl-glucosamine (NAG)
Beta1 -> 4 linked glycosidic bonds cause?
Alternate sugar residues to flip over
Beta1 -> 4 linked polysaccharides adopt?
Fully extended conformation
What makes up the structure of peptidoglycan?
Lysozyme
Peptidoglycan
Polysaccharides
What makes up a lysozyme?
Small enzyme
Composed of 129 amino acids
Large active center in relation to the size of the enzyme
Large number of hydrophobic residues exposed at the surface of the molecule: Import in binding substrate
Glu 35 and Asp 52 contributes to catalysis
What does Lysozyme use to catalyse hydrolysis?
Proximity
General acid catalysis
transition state stabilisation
Lysozyme (reaction mechanism): Glu 35 and Asp 52 lie on?
Opposite sides of the polysaccharide chain in close proximity of rings D and E:
Glu is protoned due to presence of surrounding hydrophobic residues
Lysozyme: explain general acid catalysis (step 1)
Proximity allows cleavage of glycosidic O-C4 NAG bond by proton transfer
Lysozyme: explain proposed transition state (step 2)
Ring E oligosaccharide diffuses away from the active site
Unstable -+ve charge formed on carboxonium ion intermediate is stabilised by the presence of ionised Asp52 residue
Lysozyme: Explain the reaction of carboxonium ion intermediate with OH- (or H2O)
Re-protonation of Glu35
Hydroxylation of ring D
Lysozyme: Explain ring D oligosaccharide diffuses away from the active site
The enzyme is prepared for further rounds of catalysis
