Describe two ways that repressor mechanisms operate in antibiotic resistance; one way in which an inducer ligand (antibiotic) is transmitted directly into the cell, and one way in which an inducer is sensed on the cell surface and a signal is sent into the cell.

Question

What will be an ideal response?

Answer 1

An inducer ligand (antibiotic) is transmitted directly into the cell: tetracycline efflux pumps. In E.coli, when tetracycline is absent from the cytoplasm, a repressor protein called tetR binds to an operator that blocks transcription of the tetB gene. tetB makes the protein (TetB) that is the efflux pump that removes tetracycline from the cell. When tetracycline comes into the cell, it acts as an inducer - it then binds to TetR.
That binding causes the release from the operator DNA, thereby allowing high expression of the TetB pump protein.

An inducer is sensed on the cell surface and a signal is sent into the cell: methicillin-resistant Staphylococcus aureus (MRSA). The BlaR1 protein of methicillin-resistant Staphylococcus aureus (MRSA) is a membrane protein involved in sensing of the presence of ?-lactam antibiotics and transduction of the information to the cytoplasm. The process of antibiotic recognition on the cell surface leads to activation of the zinc protease (BlaR2) in the cytoplasmic domain. The protease activity degrades BlaI, a repressor protein, resulting in derepression of the antibiotic resistance genes. These genes encode BlaZ, which is a lactamase enzyme that binds to B-lactam antibiotics, rendering them inactive.