[Localization of energy domains in Bacillus intermedius 7P ribonuclease]

Two independently melting regions (energetic domains) were localized in Bacillus intermedius 7P ribonuclease by methods of circular dichroism and high resolution X-ray analysis: the lov-temperature melting domain, containing C-terminal region of the molecule with five strands in antiparallel beta-structure and the high-temperature melting alpha-helical domain in the N-terminal region. The contact between these domains is stabilized mainly by ionic interaction Asp-22 - Lys+-48. At pH 2.4 and 30.5 0 C, when the low-temperature domain melts, half of the beta-structure content in binase is destroyed though the alpha-helical structure content is conserved. It has been shown that in pH interval 2.4-4.8 at 15 0 C no changes in secondary structure and local surrounding of aromatic amino acid residues could be identified. Thus, the changes in ionic interactions in the binase molecule due to protonation of Asp side chain groups does not effect the secondary or tertiary structure, though it changes the energetical state of the binase molecule, revealing a change of number and size of energetic domains.