What charge is typically associated with the C-terminal of a protein?

• A. Positively charged
• B. Negatively charged
• C. Neutral
• D. Varies depending on the protein

Answer: (B)

The C-terminal of a protein typically has a negatively charged carboxyl group (-COO⁻) due to the presence of a free carboxylic acid at the end of the polypeptide chain. At physiological pH (around 7.4), this carboxylic acid group tends to lose a proton (H⁺), resulting in a negatively charged overall charge. This characteristic contributes to the overall charge and behavior of the protein, influencing its interactions with other molecules, solubility, and stability.

Additionally, while some proteins may have post-translational modifications or conformational changes that can impact the charge of the C-terminus, the standard and most common state reflects a negative charge at physiological conditions.