What change occurs to pilin after modification by PptB?

• A. Increase in number of disulfide bonds
• B. Decrease in molecular weight
• C. Increase in enzymatic activity
• D. Decrease in isoelectric point

Answer: (D)

The correct answer indicates that there is a decrease in the isoelectric point of pilin after modification by the enzyme PptB. The isoelectric point (pI) is the pH at which a molecule carries no net electrical charge. This parameter can be affected by modifications that alter the charge properties of the molecule, such as the addition or removal of charged groups.

PptB is known to modify pilin, which is a protein that contributes to the formation of pili in bacteria. This modification typically involves the addition of a phospholipid moiety to the pilin molecule. Such modifications can introduce additional negative or positive charges, depending on the nature of the added molecules. For example, if the addition of a negatively charged group occurs, the overall charge of the pilin will be altered, which usually leads to a reduction in its isoelectric point.

A decrease in the isoelectric point signifies that at a lower pH, the pilin will be more negatively charged, which can affect how the protein interacts with other molecules, including its role in bacterial adhesion and biofilm formation.

In this context, the other options do not align with the expected biochemical effects of the PptB modification on pilin. The increase in