Amidase

Related Reading

In enzymology, an amidase is an enzyme that catalyzes the hydrolysis of an amide:

Figure 1. Hydrolysis of an amide.

Therefore, the two substrates of the enzyme are monocarboxylic acid amide and H2O, and its two products are monocarboxylic acid salt and NH3. This enzyme belongs to the family of hydrolases, which act on carbon-nitrogen bonds other than peptide bonds, especially in linear amides. The systematic name of this enzyme class is acylamide amide hydrolase. Other commonly used names include acylase, acyltransferase, amide hydrolase, deaminase, fatty acylase and N-acetamidohydrolase. The enzyme is involved in 6 metabolic pathways: urea cycle and amino metabolism, phenylalanine metabolism, tryptophan metabolism, cyano amino acid metabolism, benzoate degradation and styrene degradation through coa linkage. Amidase contains a conserved sequence of about 130 amino acids, called the AS sequence. They are very common and are found in both prokaryotes and eukaryotes. AS enzymes catalyze the hydrolysis of amide bonds (CO-NH2), although this family has great differences in substrate specificity and function. However, these enzymes maintain the core α/β/α structure, where the topologies of the N-terminal and C-terminal half are similar. AS enzymes are characterized by a highly conserved C-terminal region, rich in serine and glycine residues, but no aspartic acid and histidine residues, so they are different from classic serine hydrolases. These enzymes have a unique, highly conserved Ser-Ser-Lys catalytic triad for amide hydrolysis, although the catalytic mechanism of acylase intermediate formation may differ between enzymes.

β-lactamase

The production of β-lactamase is the most common mechanism of bacterial resistance to (β-lactams) antibacterial drugs, and it is widely involved in many important pathogens of community-acquired infections and hospital infections. The production of β-lactamase is the most common mechanism of antibiotic resistance, accounting for 80% of the various resistance mechanisms. Beta-lactamases are a family of enzymes composed of multiple enzymes that can hydrolyze beta-lactam antibiotics. The genes for these enzymes are present in the chromosomes or plasmids of bacteria.

Principle

β-lactam antibiotics are bactericides that inhibit the formation of peptidoglycan in bacterial cell walls. Peptidoglycan constitutes the main structure of the cell wall, especially the cell wall of gram-positive bacteria. The last step of peptidoglycan synthesis is formed by transpeptidase enzymes called pennicillin binding proteins (PBPs). Beta-lactam antibiotics are similar to D-alanyl-D-alanine, and their terminal amino acids are adsorbed on the precursor NAM-NAG peptide unit of the peptidoglycan being formed. The structural similarity between β-lactam antibiotics and D-alanyl-D-alanine allows them to bind to penicillin binding proteins. The β-lactam core irreversibly binds to the Ser403 unit of the penicillin binding protein. This irreversible binding makes the penicillin binding protein unable to link the peptidoglycan layer that is being formed. In addition, this binding may also activate autolysing enzymes in the cell wall.

Figure 2. Structure of β-lactam.

Drug resistance

β-lactam antibiotics all have a β-lactam ring. The effect of these antibiotics depends on whether they can fully reach the penicillin binding protein and whether they can bind to the penicillin binding protein. Therefore, bacteria have two methods to resist β-lactam antibiotics. The resistance method is to use enzymes to hydrolyze the β-lactam ring. By producing enzymes such as β-lactamase, bacteria can untie the β-lactam ring in antibiotics, making the antibiotics ineffective. The genes for these enzymes may be on the chromosomes of bacteria themselves, or they may be obtained through plasmid exchange. Its gene expression may have started after exposure to antibiotics.

Reference

1. Wei BQ.; et al. A second fatty acid amide hydrolase with variable distribution among placental mammals. J. Biol. Chem. 2006, 281 (48): 36569–78