Background information You have purified a protein and are n

Background information:

You have purified a protein and are now trying to determine the sequence. Using the Edman Degradation method, you receive the results M,N,Y,I,G,R.

When you digest a sample of your protein with Trypsin, you get the followingfragments:  ASTFLMR     GATWCDEK     ICYLVSK     MNYIGR     NFHPPR     MQL

Trypsin cleaves at Lysine (K) and Arginine (R)

When you digest a sample of your protein with Chymotrypsin you get a different set of fragments: MNY     LMRNF     CDEKICY     LVSKMQL     IGRASTF     HPPRGATW

Chymotrypsin cleaves at Phe (F), Trp (W), and Tyr (Y)

Question: What is the correct sequence of your protein?

Please explain clearly how you obtain the correct sequence at the end. Thanks.

Solution

Question: What is the correct sequence of your protein?

Answer:

Fragments came after digestion

Cleaves at

Trypsin

ASTFLMR                   

GATWCDEK

ICYLVSK

MNYIGR   

NFHPPR

MQL

Lysine (K) Arginine (R)

Chymotrypsin

MNY     

LMRNF     

CDEKICY         

LVSKMQL

IGRASTF   

  HPPRGATW

Phe (F), Trp (W), Tyr (Y)

Based on the available data and the fragments came after the digestion we can get the correct sequence of this protein:

MNYIGR       ASTFLMR    NFHPPR       GATWCDEK          ICYLVSK    MQL

How this comes:

Compare all the 6 fragments of both trypsin and chymotrypsin and arrange them accordingly, we can get this sequence. This is nothing but comparing the tails and filling the sequence.

Lets take Fragment 1 of Trypsin ASTFLMR see the ends LMR is found in the chymostrypsins Fragment 2 with LMRNF, NF as end, go for NF sequence in trypsin Fragment 5 is that with such sequence NFHPPR, now same Fragment 6 in Chymotrypsin, In this way complete sequence is

MNYIGR       ASTFLMR    NFHPPR       GATWCDEK          ICYLVSK    MQL