Answer:
Explanation:
Before I start, let me make one thing clear before we start solving this...I know its says that it will not cleave if it's on the N-side of Proline. HOWEVER, this does not mean the WHOLE N-side...just the immediate N-side Amino Acid. This misunderstanding really screwed me over when I was trying to solve this question.
Ok, so let's start with 10 blanks:
X-X-X-X-X-X-X-X-X-X
Cyanogen bromide cleaves after methionine and leaves a nonapeptide so methionine must be the first one
Met-X-X-X-X-X-X-X-X-X
The information from the trypsin digestion lets us know the first part of the sequence. Since Trypsin cleaves the C side of Lys and Arg, Lys must be the last amino acid
Met-Val-Lys-X-X-X-X-X-X-X
CT3 has Lys, Met, Tyr, and Val and since Met, Val, and Lys are the first three amino acids, Tyr must be the fourth:
Met-Val-Lys-Tyr-X-X-X-X-X-X
Since chymotrypsin cleaves after Tyr and Trp and the sequence is only Thr-Trp, I just put it in next. This is kinda like a "gimme" sequence.
Met-Val-Lys-Tyr-Thr-Trp-X-X-X-X
(we don't have to worry for Trp to be next to Pro since we were told that Ala is the first Amino Acid of CT1's sequence)
All we are missing now is Ala, Arg, Phe, and Pro. Since Ala is the first amino acid of the CT1, that means:
Met-Val-Lys-Tyr-Thr-Trp-Ala-X-X-X
Now this is the part where it can be tricky to explain. This is spot where you can get multiple answers depending on where you look at first or what process of elimination you are using...
There are 4 possible ways to end this sequence...Phe-Arg-Pro, Arg-Phe-Pro, Arg-Pro-Phe, or Phe-Pro-Arg. HOWEVER, Arg-Phe-Pro and Phe-Arg-Pro CANNOT work.
Why?
For Phe-Arg-Pro:
If this was the case then there should have been a CT4: Arg-Pro
For Arg-Phe-Pro:
Then there should have been a T3: Phe-Pro
So your two answers can be:
Met-Val-Lys-Tyr-Thr-Trp-Ala-Phe-Pro-Arg OR Met-Val-Lys-Tyr-Thr-Trp-Ala-Arg-Pro-Phe
