Glycine is an achiral molecule. So can it show any kind of CD spectra in any kind of condition (either in far UV or in near UV)? Will it show the CD spectra in the form of a straight line or it will follow helical pattern?
Since in the far UV region, the absorbing group is the peptide bond, far UV CD spectroscopy is used to evaluate the overall secondary structure content of the protein/peptide. Although the peptide group in isolation exhibits a plane of symmetry and is, therefore, achiral and does not exhibit intrinsic CD, its location within the highly
unsymmetrical peptide backbone acts to confer optical activity, making it an extrinsic
chromophore. Also, chirality/achirality of the side chain, typically, does not play a role in this spectral region. You definitely will have a sectrum in far UV CD region. It is likely that monomeric polyglycine will give you a polyglycine type II helix spectrum (with a strong negative band at 192 nm and a weak positive band at 210 nm). Since polyglycine has a tendency for self-aggergation and amyloidogenic, in aggregated form it will show far UV CD spectrum typical for the beta-structure.
This paper http://onlinelibrary.wiley.com/doi/10.1002/bip.1981.360200210/abstract would suggest a far-UV CD signal is present. As near-UV arises from sidechains, this is unlikely for polyglycine
Short, solubilized polyalanines are conformational chameleons: exceptionally helical if N- and C-capped with helix stabilizers, weakly to moderately helical if capped with rigid spacers.
Miller JS, Kennedy RJ, Kemp DS.
Biochemistry. 2001 Jan 16;40(2):305-9.
2. Structure and dynamics of elastin building blocks. Boc-LG-OEt, Boc-VGG-OH.
Martino M, Bavoso A, Saviano M, Di Blasio B, Tamburro AM.
J Biomol Struct Dyn. 1998 Apr;15(5):861-75.
Read these reprints
Wonderful material for you in this chapter
http://www.chem.uky.edu/courses/che230/FL/chapter4.pdf
Since in the far UV region, the absorbing group is the peptide bond, far UV CD spectroscopy is used to evaluate the overall secondary structure content of the protein/peptide. Although the peptide group in isolation exhibits a plane of symmetry and is, therefore, achiral and does not exhibit intrinsic CD, its location within the highly
unsymmetrical peptide backbone acts to confer optical activity, making it an extrinsic
chromophore. Also, chirality/achirality of the side chain, typically, does not play a role in this spectral region. You definitely will have a sectrum in far UV CD region. It is likely that monomeric polyglycine will give you a polyglycine type II helix spectrum (with a strong negative band at 192 nm and a weak positive band at 210 nm). Since polyglycine has a tendency for self-aggergation and amyloidogenic, in aggregated form it will show far UV CD spectrum typical for the beta-structure.
Dear Volodya, As stated here: J Phys Chem B. 2010 May 20; 114(19): 6636–6641. , http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2879021/ " gly has no chiral atoms, which means that polygly can not be studied by CD, the standard method used for secondary structure analysis of peptides and proteins in solution." However, as Matthew suggests, experimental evidence may suggest otherwise. There is one person who may have collected that data, although I see no papers from her group. That would be Bonnie Wallace: http://people.cryst.bbk.ac.uk/~ubcg25a/ Send her your question. She will have the data, or know someone who does. Best, Bob
Dear Bob,
Thanks for the clarifications. You are right. I saw several papers talking about the polyGly analysis, but in all the cases CD was done for the co-polymers containing majority of Gly and some other residues.
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