BCH 4053--General Biochemistry I--Spring 2003 |
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This is to be done as a group project. At least two persons must work together, but three or more is okay. The problem is worth six points as follows:
The problem is due in class on Friday, February 14. Please make your submission legible and in pencil or pen dark enough for me to read.
To save time in sequencing, sometimes the Edman degradation procedure can be run on a mixture of peptides without first separating them. The results are like a jigsaw puzzle which one can then piece together to get the overall sequence. The following data are sufficient to deduce a complete sequence for the small protein described.
1. A small protein, containing only 40 amino acid residues was reduced and carboxymethylated to alkylate the cysteine residues and then characterized as follows:
(a) Edman degradation gave Asp as N-terminal.
(b) CNBr cleavage, followed by Edman sequencing of the unfractionated mixture of peptides gave the following sets of amino acids in each round of sequencing (each set listed in alphabetical order; data beyond the 8th round were not reliable):
Round
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1
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2
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3
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4
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5
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6
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7
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8
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Amino Acids: | Arg | Gln | Asn | Arg | Asn | Arg | Ala | Ala |
Asp | Pro | Pro | His | Ilu | His | Gly | Lys | |
Glu | Thr | Ser | Ilu | Leu | Trp | Phe | Met | |
Gly | Tyr | Tyr | Val | Phe | Val | Thr | Tyr |
Note: This means that in the first round of the Edman, Arg, Asp, Glu and Gly were released, indicating four peptides with these amino acids as N-terminal. On the next round, Gln, Pro, Thr, and Tyr were released, etc.
(c) Trypsin digestion followed by Edman sequencing of the unfractionated mixture of peptides gave the following sets of amino acids in each round of sequencing (each set listed in alphabetical order; data beyond the 8th round were not reliable.): (Cys indicates carboxymethylcysteine.)
Round
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1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
Amino Acids: | Asp | Cys | His | Ala | Ilu | Arg | Cys | Glu |
Gly | His | Met | Asn | Leu | Phe | Lys | Leu | |
Gly | Pro | Thr | Glu | Thr | Ser | Ilu | ||
Phe | Pro | Tyr | Val | Trp | Ser | |||
Tyr | Tyr |
Note this time there were five peptides, one of them only two amino acids long, one of them six long, one seven, and two eight or longer.
Deduce the sequence of this 40-residue peptide from this information.
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