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5. A product ion (MS/MS) spectrum of a tryptic peptide

\mathbf{T}

was acquire...

Sep 23, 2024

Solution

Identify the sequence of the tryptic peptide: The precursor ion at

m/z = 617.3617

indicates that the peptide has a mass of approximately 617.36 Da. By analyzing the sequences of the proteins provided, we can determine the possible tryptic peptide sequences. The tryptic digestion will yield peptides that are typically between 6-30 amino acids long. The only sequence that matches the mass of 617.36 Da is derived from Protein I, which is

RLTARLEALKP

Identify the unknown protein: Since the identified peptide sequence

RLTARLEALKP

corresponds to Protein I, we can conclude that the unknown protein is Protein I. This is justified because the mass of the identified peptide matches the precursor ion mass, confirming its origin from Protein I

Predict and sketch the MALDI positive charge ion mass spectrum: The MALDI mass spectrum for the tryptic digested peptides from Protein I will show peaks corresponding to the masses of the generated peptides. The most abundant peaks will likely correspond to the identified peptide

RLTARLEALKP

and other smaller peptides resulting from the digestion. The x-axis will represent the

m/z

values, while the y-axis will represent the relative abundance of the ions detected. The peaks will be distributed based on the masses of the peptides generated from the tryptic digestion

Answer

The identified tryptic peptide is

RLTARLEALKP

from Protein I, confirming it as the unknown protein. The MALDI spectrum will show peaks corresponding to the masses of the tryptic peptides.

Key Concept

Tryptic digestion and mass spectrometry are essential techniques in proteomics for identifying proteins and their fragments.

Explanation

The analysis of the mass spectrum allows for the identification of peptide sequences and the corresponding proteins from which they originate. The MALDI spectrum provides insight into the distribution of peptide masses.