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Chemical structure of Penicillin G. The sulfur and nitrogen of the five-membered thiazolidine ring are shown in yellow and blue respectively. The image shows that the thiazolidine ring and fused four-membered β-lactam are not in the same plane. The term "penam" is used to describe the common core skeleton of a member of the penicillins.
PBPs bind to β-lactam antibiotics because they are similar in chemical structure to the modular pieces that form the peptidoglycan. [10] When they bind to penicillin, the β-lactam amide bond is ruptured to form a covalent bond with the catalytic serine residue at the PBPs active site. This is an irreversible reaction and inactivates the enzyme.
β-Lactam antibiotics are indicated for the prevention and treatment of bacterial infections caused by susceptible organisms. At first, β-lactam antibiotics were mainly active only against gram-positive bacteria, yet the recent development of broad-spectrum β-lactam antibiotics active against various gram-negative organisms has increased their usefulness.
Penicillin core structure. The β-lactam ring is part of the core structure of several antibiotic families, the principal ones being the penicillins, cephalosporins, carbapenems, and monobactams, which are, therefore, also called β-lactam antibiotics. Nearly all of these antibiotics work by inhibiting bacterial cell wall biosynthesis.
Beta-lactam antibiotics such as penicillin inhibit the formation of peptidoglycan cross-links in the bacterial cell wall. The enzyme lysozyme , found in human tears, also digests the cell wall of bacteria and is the body's main defense against eye infections.
This enzyme is an excellent drug target because it is essential, is accessible from the periplasm, and has no equivalent in mammalian cells. DD-Transpeptidase is the target protein of β-lactam antibiotics (e.g. penicillin). This is because the structure of the β-lactam closely resembles the D-ala-D-ala residue.
The chemical structure of penicillin was first proposed by Abraham in 1942 [151] and then later confirmed by Dorothy Crowfoot Hodgkin in 1945. Purified penicillin displayed potent antibacterial activity against a wide range of bacteria and had low toxicity in humans.
This class of antibiotics is the most widely used. They act by inhibiting the synthesis of the peptidoglycan layer of bacterial cell walls, which is especially important in Gram-positive organisms. There are several types of penicillins that can be used to treat different kinds of bacterial infections. [7]