[The unusual thermodynamic properties of compact forms pFh fragments (hinge region) IgG3 Kuc and Sur]

pFh fragments from the hinge region of human IgG3 Kuc and Sur can fold into compact form, resulting the formation of proteins with secondary (super-secondary) structure, which is represented almost exclusively double poly-L-proline helix. It was demonstrated by several methods that the thermal denaturation of compact form pFh fragment (hinge region) IgG3 Kuc and Sur occurs in two stages. The "two-state" model described the disintegration of the compact structure with preservation of the secondary structure (double poly-L-proline helix). In the second stage melts itself helix consisting of four cooperative units, which are formed by the sections with a high content of proline residues. Poliproline conformation of secondary structure and large number of disulfide bonds is responsible for high specific enthalpy of denaturation and high thermal stability.