Secondary structure of tubulin on the evidence of Fourier transform infrared spectroscopy investigation

Fourier transform infrared technique is used for identifying secondary structure of GTP/GDP tubulin in the absorbancy region of its amide-I band. With this technique the band was initially resolved for 3 main and 4 satellite maxima, subsequently taken as starting values for computer resolution of the band into components of Gaussian line shape. A resolution of the spectrum into components was carried out with the FUMILI software; the resolution error was 1,5%. Improved maxima positions for the resolved components of GTP tubulin spectrum are as follows: 1682,2; 1663,7; 1653,2; 1633,4; 1625,4; 1614,0; 1605,7 cm(-1) each assigned to the vibrations of a definite structural type of the protein. The main part of the structure, similar to 50%, corresponds to beta-antiparallel sheet, the contribution of alpha-coils is about of 25%. GDP tubulin shows the contribution of beta-antiparallel sheet to be greater and the contribution of alpha-coil to be less than in GTP tubulin. The difference in the maxima positions of GTP and GDP tubulin spectra does not exceed the value of +/-3 cm(-1).