GIGSGPDLVAEFMMKAWLQGSS

We mutated the W into an R and got much better binding to a regulatory element. The following sequence is the C-terminal peptide of the protein kannietus from the related bacillus bacillus thermotaga:

SSAAELLRAFAQLLAMGGSASG

Which residue would you mutate in the kannietus from bacillus thermotaga to get the same improved binding to the similar regulatory element in this bacillus? Motivate your answer in less than 20 words.

The two sequences align like:

GIGSGPDLVAEFMMKAWLQGSS---
                |
---SSAAELLRAFAQLLAMGGSASG

The alignment is based on the correspondence of the two aligned/predicted helices. The W ligns up with the second L of the LL pair. Normally, similar positions in a structure have similar functions.