Substituting the residue at position 54 of BvgA with which amino acid will least likely prevent the expression of the PTx operon?

• A. Glycine
• B. Asparagine
• C. Glutamate
• D. Alanine

Answer: (C)

The expression of the PTx operon in bacteria is regulated by the BvgAS two-component system, where BvgA acts as a response regulator. The residue at position 54 in BvgA likely plays a crucial role in the protein’s functionality, particularly in the activation of operons like PTx.

Substituting this residue with an amino acid that retains similar chemical properties or maintains the structural integrity of the protein can lead to continued expression of the PTx operon. Glutamate, being a negatively charged amino acid, may disrupt the activation function of BvgA, depending on the specific interactions and the biochemical environment at that position. This disruption could result in reduced or no expression of the operon.

In contrast, substituting with asparagine, which has a similar size and can form hydrogen bonds like the original residue, or with glycine, which is small and flexible, could allow the protein to maintain its functionality more effectively. Alanine, being a nonpolar, relatively neutral amino acid, may also not significantly impact the functionality of BvgA due to its similar hydrophobic character.

Thus, substituting the residue at position 54 with glutamate is least likely to prevent the expression of the PTx oper