How might second mutation lead to restoration of activity

1) A mutation that changes an alanine residue in the interior of a protein to valine is found to lead a loss of activity. However, activity is regained when a second mutation at different position changes an isoleucine residue to glycine. How might this second mutation lead to restoration of activity?

2) Identify the functional groups in side chain of a protein that can form hydrogen bonds or electrostatic interactions with a side chain of arginine within the same protein with pH of 7.0.

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