Question

Give the amino acid sequence of hexapeptides that produce the following sets of fragments upon partial acid hydrolysis: (a) Arg, Gly, lle, Leu, Pro, Val gives Pro-Leu-Gly, Arg-Pro, Gly-Ile-Val (b) \(\mathrm{N}, \mathrm{L}, \mathrm{M}, \mathrm{W}, \mathrm{V}_{2}\) gives \(\mathrm{V}-\mathrm{L}, \mathrm{V}-\mathrm{M}-\mathrm{W}, \mathrm{W}-\mathrm{N}-\mathrm{V}\)

Short answer

(a) Arg-Pro-Leu-Gly-Ile-Val; (b) V-L-M-W-N-V.

Step-by-step solution

Analyze Peptide A Fragments

We have the fragments: Pro-Leu-Gly, Arg-Pro, and Gly-Ile-Val. These fragments suggest the amino acid sequence of the hexapeptide has the sequence Arg-Pro-Leu-Gly-Ile-Val, ensuring overlapping residues in the fragments are joined.

Verify Hexapeptide A

Check if this sequence Arg-Pro-Leu-Gly-Ile-Val gives the overlapping fragments: - Pro-Leu-Gly (in the middle) - Arg-Pro (at the start) - Gly-Ile-Val (at the end) Since all fragments fit, this sequence is correct for the given fragments.

Analyze Peptide B Fragments

For peptide B, the fragments are V-L, V-M-W, and W-N-V. Start with overlapping fragments: W from V-M-W and W-N-V matches, suggesting a sequence order. Construct the sequence as V-L-M-W-N-V, ensuring all fragments overlap correctly.

Verify Hexapeptide B

Check the constructed sequence V-L-M-W-N-V to ensure it gives the specified fragments: - V-L, at the start - V-M-W, starting at the beginning - W-N-V, starting at W towards the end All fragments fit, confirming the sequence matches the given fragments.

Key concepts

Amino Acid Sequence

To understand peptide structure, one must first grasp the concept of amino acid sequences. An amino acid sequence refers to the unique order of amino acids in a peptide or protein, determined by their genetic coding. Each sequence dictates the protein's structure and function.
This sequence is like a biological "sentence," where each "word" is an amino acid. The sequence determines how the peptide folds into its three-dimensional shape, directly influencing its biological activity.
When analyzing hexapeptides, as in our problem, we deal with sequences of six amino acids. The challenge lies in deducing these sequences based on given fragment data by reassembling the complete sequence from overlapping segments.
Understanding these basics helps you unravel complex peptide structures using minimal information.

Partial Acid Hydrolysis

Partial acid hydrolysis is a method used to break down peptides into smaller fragments without completely severing all bonds. It's like a gentle digestive process, providing insight into how amino acids are arranged without destroying them entirely.
During this process, the peptide bonds—links between amino acids—are selectively broken. The method typically targets the more vulnerable bonds, allowing researchers to deduce the sequence based on how the peptide fragments.
This technique is essential for peptide sequence analysis, as it helps identify overlapping fragments, shedding light on the original amino acid sequence. By creating patterns of segments, researchers can piece together the puzzle of peptide structure.

Hexapeptide Fragmentation

Hexapeptide fragmentation involves breaking a six-amino acid chain into smaller, overlapping segments. This process reveals clues about their original sequence.
For instance, if you have fragments like Pro-Leu-Gly and Arg-Pro, the overlapping Pro indicates their sequence proximity. By matching such overlaps, the full sequence is reconstructed.
This technique is akin to solving a jigsaw puzzle where each piece must fit perfectly with another. Correct sequence determination lets biologists understand protein function and design synthetic peptides.
Recognizing significant segments and overlaps in fragments simplifies constructing the complete picture of the hexapeptide sequence, facilitating deeper biochemical insights.