How B-lactam drugs work: Difference between revisions
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The beta lactam antibiotic <scene name='81/814024/B_lactam_in_hole/1'>binds in this groove of the protein</scene>. The groove also contains a <scene name='81/814024/Ser_62/1'>serine residue</scene> that is important for the catalysis of the peptide bond formation. Instead of reacting with the normal peptide substrate, the serine residue has formed a <scene name='81/814024/Ser_62_measurement/1'>covalent bond</scene> with the carbonyl carbon of the beta lactam, as can be seen by its bond length (a C-O bond is 0.14 nm), and the increased distance between the carbonyl carbon and the <scene name='81/814024/C_n_bond_measurement/1'>nitrogen it bonds to in the lactam ring</scene> (a normal C-N bond distance is 0.15 nm; this is almost double that distance). | The beta lactam antibiotic <scene name='81/814024/B_lactam_in_hole/1'>binds in this groove of the protein</scene>. The groove also contains a <scene name='81/814024/Ser_62/1'>serine residue</scene> that is important for the catalysis of the peptide bond formation. Instead of reacting with the normal peptide substrate, the serine residue has formed a <scene name='81/814024/Ser_62_measurement/1'>covalent bond</scene> with the carbonyl carbon of the beta lactam, as can be seen by its bond length (a C-O bond is 0.14 nm), and the increased distance between the carbonyl carbon and the <scene name='81/814024/C_n_bond_measurement/1'>nitrogen it bonds to in the lactam ring</scene> (a normal C-N bond distance is 0.15 nm; this is almost double that distance). This prevents the normal substrate, the D-ala peptide fragments, from binding to the enzyme, preventing the crosslinking of the bacterial cell wall. Because the antibiotic is attached to the enzyme via a covalent bond, it doesn't come off easily, and the enzyme is essentially "dead". | ||
How do bacteria become resistant to penicillin and other beta lactam antibiotics? Some bacteria have an enzyme called penicillinase, which inactivates penicillin by cutting the beta lactam ring to form a carboxylic acid and an amine. This prevents the antibiotic from reacting with the serine residue in the transpeptidase, making it inactive. The gene for this enzyme is located on a bacterial plasmid, and can be transferred from one bacteria to another, causing antibacterial resistance to spread. | |||