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Chapter 5: Q31P. (page 129)

You wish to determine the sequence of a short peptide. Cleavage with trypsin yields three smaller peptides with the sequences Leu鈥揋lu, Gly鈥揟yr鈥� Asn鈥揂rg, and Gln鈥揂la鈥揚he鈥揤al鈥揕ys. Cleavage with chymotrypsin yields three peptides with the sequences Gln鈥揂la鈥揚he, Asn鈥揂rg鈥揕eu鈥揋lu, and Val鈥揕ys鈥揋ly鈥揟yr. What is the sequence of the intact peptide?

Short Answer

Expert verified

The intact peptide will have the sequence:

Ile-Ala-Tyr-Val-Arg-Gly-trp-asn-Lys-Leu-Glu

Step by step solution

01

Protein sequencing

For sequencing a protein, the protein must first be broken down into small fragments.Endopeptidases like pepsin, trypsin, chymotrypsin, etc. can be used to cleave the peptide into smaller fragments. The peptide is cleaved using two different peptidases to yield two different sets of fragments. Then the amino acid sequence of each of the fragments is determined. After this, the fragments are overlapped to reconstruct the sequence of the whole polypeptide.

02

Explanation

The small peptides obtained through cleavage with trypsin and chymotrypsin are overlapped to determine the sequence of the polypeptide.

Thus, the sequence of the intact polypeptide is:

Ile-Ala-Tyr-Val-Arg-Gly-trp-asn-Lys-Leu-Glu

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Most popular questions from this chapter

You are using ammonium sulphate to purify protein Q (pI = 5.0) by salting out from a solution at pH 7.0. How should you adjust the pH of the mixture to maximize the amount of protein Q that precipitates?

Treatment of a polypeptide with 2-mercaptoethanol yields two polypeptides:

1. Ala鈥揤al鈥揅ys鈥揂rg鈥揟hr鈥揋ly鈥揅ys鈥揕ys鈥揂sn鈥揚he鈥揕eu

2. Tyr鈥揕ys鈥揅ys鈥揚he鈥揂rg鈥揌is鈥揟hr鈥揕ys鈥揅ys鈥揝er

Treatment of the intact polypeptide with trypsin yields fragments with the following amino acid compositions:

3. (Ala, Arg, Cys2, Ser, Val)

4. (Arg, Cys2, Gly, Lys, Thr, Phe)

5. (Asn, Leu, Phe)

6. (His, Lys, Thr)

7. (Lys, Tyr)

Indicate the positions of the disulfide bonds in the intact polypeptide.

Question: Purification tables are often used to keep track of the yield and purification of a protein. The specific activity is a ratio of the amount of the protein of interest, in this case Mb, obtained at a given step (渭mol or enzyme units) divided by the amount (mg) of total protein. The yield is the ratio of the amount of the protein of interest obtained at a given step (渭mol or enzyme units) divided by the original amount present in the crude extract, often converted to percent yield by multiplying by 100. The fold purification is the ratio of the specific activity of the purified protein to that of the crude preparation.

(a) For the purification table below, calculate the specific activity, % yield, and fold purification for the empty cells.

(b) Which step鈥擠EAE or affinity chromatography鈥攃auses the greatest loss of Mb?

(c) Which step causes the greater purification of Mb?

(d) If you wanted to use only one purification step, which technique would you choose?

Which peptide has greater absorbance at 280 nm?

A. Gln鈥揕eu鈥揋lu鈥揚he鈥揟hr鈥揕eu鈥揂sp鈥揋ly鈥揟yr

B. Ser鈥揤al鈥揟rp鈥揂sp鈥揚he鈥揋ly鈥揟yr鈥揟rp鈥揂la

Protein X has an absorptivity of 0.4mL 路 mg-1路 cm-1 at 280nm. What is the absorbance at 280nm of a 2.0 mg 路 mL-1solution of protein X? (Assume the light path is 1cm.)
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