THE MEASUREMENT OF TRANSMEMBRANE HELICES BY THE DECONVOLUTION OF CD SPECTRA OF MEMBRANE-PROTEINS - A REVIEW

The interpretation of the CD spectra of proteins to date requires addi tional secondary structural information of the proteins to be analyzed , such as x-ray or nmr data. Therefore, these methods are inappropriat e for a CD data base whose secondary structures are unknown, as in the case of the membrane proteins. The Convex Constraint Analysis algorit hm [A. Perczel, M. Hollosi, G. Tusnady, and G. D. Fasman (1991) Protei n Engineering, Vol. 4, 669-679], on the other hand, operates only on a collection of spectral data to extract the common spectral components with their spectral weights. The linear combinations of these derived ''pure'' CD curves can reconstruct the original data set with great a ccuracy. For a membrane protein data set, the five- component spectra so obtained from the deconvolution consisted of two different types of alpha-helices (the alpha-helix in the soluble domain and the alpha(T) -helix, for the transmembrane alpha-helix), a beta-pleated sheet, a cl ass C-like spectrum related to beta-turns, and a spectrum correlated w ith the unordered conformation. The deconvoluted CD spectrum for the a lpha(T)-helix was characterized by a positive red-shifted band in the range 195-200 nm (+95,000 deg cm(2) dmol(-1)), with the intensity of t he negative band at 208 nm being slightly less negative than that of t he 222 nm band (-50,000 and -60,000 deg cm(2) dmol(-1), respectively) in comparison with the regular alpha-helix, with a positive band at 19 0 nm and two negative bands at 208 and 222 nm with magnitudes of +70,0 00, -30,000, and -30, 000 deg cm(2) dmol(-1), respectively. (C) 1995 J ohn Wiley & Sons, Inc.