CTX-M Beta-Lactamase
CTX-M Beta Lactamase is a class a enzyme. This enzyme creates drug resistance to ampicillin and cefotaxime through a two step process: deacylation and acylation.
Function of Protein
CTX-M Beta-Lactamase is an enzyme that is produced in bacteria, more specifically E. coli. CTX-M Beta-Lactamase is made to inhibit Beta-Lactam. Beta-Lactam binds with ampicillin and cefotaxime, which are both made to fight bacterial infections. It attacks the lactam ring that are in both of these structures, which causes deacylation to occur. is the overall structure of CTX-M Beta-Lactamase.
Biological Relevance and Broader Implications
Since Beta-Lactam antibiotics are used very often in antimicrobial therapy to treat bacterial infections, bacterial resistance often ocurrs. This enzyme, CTX-M Beta-Lactamase, inhibits the drug's function by breaking apart the lactam ring, making it harder to treat. This is a problem because if we can understand it better, we can change the way we treat to fight off the bacteria better.
The research of this protein is very significant because it has a direct clinical application.
Important Amino Acids
The important amino acids that are in CTX-M Beta-Lactamase include Ser70, Ser130, Lys73, Lys234, and Arg234. The residue at 234 undergoes a mutation in some cases, which can then be either a Lys or an Arg.
The consists of the residues 70,130, an 234. The Ser70 attacks the carbonyl carbon on the lactam ring an then is protonated to create an alcohol which ends in it breaking off once again. It also interactions with the oxygen on the ampicillin, and it is cross-linked with the clavulanic acid. Ser130 helps to the amide bond and then distributes to a proton of the nitrogen. Ser130 is also cross-linked with clavulanic acid and interacts with the ligand through hydrogen bonds.
Structural highlights
This protein has eight chains. Each chain has eleven separate and nine separate . Some of the chains bind to to help with stability. Within each chain, there are two of the catalytic amino acid within helix three. The last catalytic amino acid is located in helix seven. Both of these helices form important interactions with the ligands because of those catalytic amino acids. The tertiary structure of the protein mainly upheld by hydrogen bonds and other noncovalent bonds. Amino acids are closer when in the tertiary structure than in the secondary structure due to the sequence. The quaternary structure has multiple chains.
is a space fill of CTX-M Beta-Lactamase, which shows where the interactions are in between each domain and where the active sites are located.
is a view of hydrophobic interactions that are within domain A of the enzyme.
Other Important Features
There have been several inhibitor-resistant variants that mutations have risen from. More specifically one of them being K23YR. This mutation causes a 1500-fold decrease in the cefotaxime and a 5-fold increase in the Kcat for ampicillin. This makes it become a good penicillinase, but a poor cephalosporinase due to slow acylation. The mutation of this will lead to the enzyme being inactivated, making the drug resistance not work efficiently.
