CONFORMATION OF TURKEY OVOMUCOID 3RD DOMAIN IN SOLUTION - A STRUCTURAL-ANALYSIS BASED ON 2-DIMENSIONAL NUCLEAR OVERHAUSER EFFECT SPECTROSCOPY DATA

Using a previously described method [12, 13, 14, 15] the conformations of the polypeptide chain of the turkey ovomucoid third domain (TO3) and its modified form with a cleaved Leu-18-Glu-19 peptide bond in the active center were determined according to two-dimensional nuclear Overhauser effect spectroscopy data [18, 19]. It was established that the polypeptide skeleton of TO3 contains the alpha-helical-fragment (residues 32-47), five regions with an "elongated" conformation (1-5, 11-17, 19-25, 29-31, 48-50), and a type I beta-turn (26-29). In this case segments 23-26, 28-31, and 50-51 form an antiparallel beta-structure. The conformational states of the residues within the irregular regions of the domain were analyzed. It was shown that cleavage of the Leu-18-Glu-19 peptide bond leads to insignificant changes in the conformations of a number of amino acid residues. Residues Val-6 and Asp-7 were exceptional. As a result of the modification these residues undergo significant conformational rearrangements. The conformations of TO3 in solution and Japanese quail ovomucoid third domain in the crystal were compared. The mean square deviation values obtained for the phi and psi-angles indicate that they exhibit a high degree of similarity. A comparative analysis was carried out on the conformation of TO3 and the bull semen plasma protease inhibitor in solution. It was shown that despite the relatively low homology of the primary structures (50%) approximately 75% of the amino acid residues have close conformational phi and psi-parameters.