Consider the following peptide which N-terminally acetylated and C-terminally am
ID: 55911 • Letter: C
Question
Consider the following peptide which N-terminally acetylated and C-terminally amidated: EIAQLEFEISQLEFEIQALES.
a) Based on the sequence alone, what structure do you expect this peptide will adopt? Make sure you correlate your answer with specific aspects of the peptide sequence.
b) The CD and FT-IR spectra (run as an ATR spectra of a dried film) of this peptide at different temperatures are provided below. What is the structure at low temperature (5°C on CD and 25°C on FT-IR)? Do the CD and FT-IR analysis agree or disagree? What about at higher temperature (55°C in CD and 50°C in FT-IR)? Do the two techniques agree at this higher temperature?
c) Is your analysis of the sequence in part (a) consistent with the experimental findings in part (b)? Why or why not?
Explanation / Answer
* The peptide will have an alpha helix, due to the high content of glutamate, alanine, leucine, all of which have have propensity to form an alpha helix or a helical strucutre.
* From the CD pictures, it is clear that at 50 C , the protein shows negative bands at 222nm and 208 nm, which interprets that the protein has an Alpha helix conformation at this temperature.
* AT 55 C, the line shows a negative band at 218 and positive band at 196 nm, which interprets that the protein has a Beta sheet conformation at this temperature.
* The FT-IR results are in accordance with the CD reuslts. The amide I frequencymax at 1652 cm-1 and the amine II abs at 1548 indicate the strucuture is a stable alpha helix ( a beta sheet will have maximum absorbance at 1625 and 1690 cm-1)