The selected phage will have sequences of the form XFYXXSLI. One of the selected
ID: 212682 • Letter: T
Question
The selected phage will have sequences of the form XFYXXSLI. One of the selected phage from the problem displays a peptide with the sequence SFYDNSLI. Predict the results of an alanine scan of this peptide.
Table I: Identity of hGH Mutants from Three Separate Libraries after Various Cycles of Binding Selection to Immobilized hGHbp helix 4a library hGH elution helix 4a library Gly, pH 2, elution K172 E174 F176 R178 K172 E174 F176 R178 One Cycle Y R Y R F H W R D R G N N E Three Cycles K A Y R (3) Y R F R (2) R S Y K Y T Y R Y H Y R Y R K Q YR K T Y K M R Consensus 172 74 176 178 Y R helix 1 library Gly, pH 2, elution helix 4b library Gly, pH 2, elution F10 M14 H18 H2 R167 D17 T175 1179 Four Cycles H G N N A W DN (2) K Y T V N F G A T A N T N T N Six cycles HG N N (6) N S T T (2) S T H GExplanation / Answer
Alanine scanning is a molecular biology technique used to determine the significance of a specific amino acid residue in a polypeptide to its structure and function. This is typically attained by changing a specific amino acid to alanine and observe the effect the protein structure and function.
Alanine is used in this technique because of the following reasons:
In the given experiment,
Consensus sequence = XFYXXSLI
So, first, fourth and fifth amino acid positions are dispensable.
If we replace first, fourth and fifth amino acids with alanine, Kd values will not change.
If we replace the other (excluding first, fourth and fifth) amino acids with alanine, Kd values would not change (Most likely to increase. Though, the decrease can also be seen in a very few cases).