An all-alpha helical protein changes a 208/222 nm ratio on its far UV CD spectrum. Any suggestions?

07 July 2017 1 4K Report

Some modification changes the CD spectrum of a small helical protein so that the 208nm band becomes more pronounced relative to the 222 band. Are there any reliable interpretations? Paper suggestions are very welcome.

Pavel I. Semenyuk

Hi,

Many reasons are possible. First, the ratio 208/220 is 2 for 3-10 helix. See for example http://pubs.acs.org/doi/full/10.1021/ja9537383 and maybe http://pubs.rsc.org/en/content/articlehtml/2009/ob/b823559g and other. 3-10 helix can be formed during alpha helix unfolding.

I read somewhere (but I can't find the paper that the ratio depends on the length of the helix (the longer, the higher 208 peak).

Finally, classical paper (Greenfield, N.; Fasman, G. D. Biochemistry 1969, 8, 4108–4116.) says that a slight change of the ratio can be observed even when percentage of alpha-helices decreases.

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