CTX-M Beta-Lactamase is an enzyme made to inhibit Beta-Lactam. It is found within bacteria, specifically the E. coli bacteria. Beta- Lactam binds with and , both of which are types of drugs made to fight bacterial infections. Beta-Lactam specifically attacks the lactam ring within both of these structures using a deacylation.
Biological relevance and broader implications
This enzyme inhibits the drug's function by breaking apart the lactam ring. This is does cause drug resistance within the E. coli bacteria making it much harder to treat via drug therapies.
Important amino acids
The important amino acids within the CTX-M Beta Lactamase are Ser70, Ser130, Lys234, Arg234, and Lys73. This creates the with one proton shuttle. The residue at 234 does undergo a mutation in some cases and therefore can be either a Lys, or an Arg. The catalytic triad are the residues at 70, 130, and 234. The S130 helps to cleave the amide bond and distributes a proton to the nitrogen. S70 attacks the carbonyl carbon on the lactam ring before also protonating to create an alcohol and it breaks off again. K73 does work as a proton shuttle for both parts of the reaction.
Structural highlights
This protein has eight chains. Each has eleven separate alpha helixes, and nine separate beta sheets. Some of the chains do bind to a GOL to help with stability. Within each chain, there are two of the catalytic amino acids within helix three. The last catalytic amino acid is located in helix seven. Both of those helices form important interactions with the ligands because of those.
The important is how the protein folds to allow the amino acids in the catalytic triad to be near each other because in the sequence, the amino acids are not near each other. By folding, the protein is able to create the binding pocket that holds the catalytic amino acids that help Beta- Lactamase function normally.
In the view of the enzyme, you can see the small binding pocket that is created to hold the substrate better.
Other important features
As previously mentioned, this enzyme does also utilize a at residue 73. This is to help shuttle protons through the reaction. S170 uses it in the first part of the reaction and Glu166 is activated by this as well, and completes the reaction, as well as recreates the S170, by donating more protons. This can allow the enzyme to work multiple times and retain it's function overtime which is not good in regards to drug resistance.
Another interesting feature is the K234 as it doesn't actually bond with the substrate like the S130, but instead works to lower the pKa of the S130, so that it is more likely to donate a proton.
