Question

A nonapeptide was determined to have the following amino acid composition: (Lys)2, (Gly) 2, (Phe) 2, His, Leu, Met. The native peptide was incubated with 1-fluoro-2,4-dinitrobenzene (FDNB) and then hydrolyzed; 2,4-dinitrophenylhistidine was identified by HPLC. When the native peptide was exposed to cyanogen bromide (CNBr), an octapeptide and free glycine were recovered. Incubation of the native peptide with trypsin gave a pentapeptide, a tripeptide, and free Lys. 2,4-Dinitrophenyl-histidine was recovered from the pentapeptide, and 2,4-dinitrophenylphenylalanine was recovered from the tripeptide. Digestion with the enzyme pepsin produced a dipeptide, a tripeptide, and a tetrapeptide. The tetrapeptide was composed of (Lys) 2, Phe, and Gly. The native sequence was determined to be:

Answer 1

The native sequence of the nonapeptide is:

His-Leu-Phe-Gly-Lys-Lys-Phe-Met-Gly

Step-by-step explanation:

The analysis of protein structures is complex, but also very specific by using endoproteases with selective cleaving of certain peptide bonds to generate peptide fragments proteolysis.

In accordance to the literature:

The FDNB (Sanger reagent) will react with the N-terminal amino acid of the peptidic chain. Then it will hydrolyse the intermediate, but it will mark only the alpha amino group (initial aminoacid).

His / FDNB / Leu-Phe-Gly-Lys-Lys-Phe-Met-Gly

The CNBr will selectively cleave the C-terminal end of methionine

His-Leu-Phe-Gly-Lys-Lys-Phe-Met / CNBr / Gly

Trypsin will selectively cleave two aminoacids, Arg and Lys (Arg >Lys) .

His-Leu-Phe-Gly-Lys / TPS / Lys / TPS / Phe-Met-Gly

Pepsine will selectively cleave the aminoacids Phe>>Leu>>Trp>Ala>other hydrophobic aminoacids.

His-Leu-Phe/ Peps / Gly-Lys-Lys-Phe / Peps / Met-Gly

Yu, Y. Q., Gilar, M., Lee, P. J., Bouvier, E. S., & Gebler, J. C. (2003). Enzyme-friendly, mass spectrometry-compatible surfactant for in-solution enzymatic digestion of proteins. Analytical chemistry, 75(21), 6023-6028.