The protein vMIP-II from Kaposi's sarcoma-associated herpesvirus (which subverts the host immune system by blocking the migration of white blood cells) consists of a 3-stranded β-sheet packed against an α-helix.

The side chain of residue Lys-61 is located on the exposed surface of the α-helix.

Examine the structure of vMIP-II (in the vicinity of Lys-61) in the PDB 3D View or by downloading the PDB file 1HFG into PyMOL.

Which of the following mutations is most likely to result in a new ionic interaction with the side chain of Lys-61, causing the folded structure of vMIP-II to be more stable at neutral pH (but not at pH 3 or pH 11)?