2.4.2. Temperature Stability of OM Porin from *M. primoryensis* KMM 3633T

The instability of MpOmp trimer was demonstrated by heating a protein sample at different temperatures. As follows from the data of SDS-PAGE (Figure 1C), protein samples of MpOmp, both isolated by POE extraction and obtained by treatment of the cell membrane with Sarcosyl, are equally temperature sensitive. Dissociation of the oligomeric form of the protein into monomers was observed already at a temperature of 30 ◦C. In order to analyze the changes in the spatial structure of porin upon heating and to differentiate the dissociation process from the process of protein denaturation, CD spectra in the peptide region and emission of MpOmp samples heated at different temperatures from 30 to 80 ◦C were recorded.

As follows from the data in Figure 3C–F, in MpOmp molecule in POE solution, changes at the level of the secondary structure of the protein are observed starting at a temperature of 40 ◦C. Further heating of the sample leads to more significant changes, manifested in a decrease in the ellipticity of characteristic peaks.

In the SDS solution in the spatial structure of the porin molecule, more serious rearrangements even occur at 30 ◦C, a change in the peak ratio at 195 and 207 nm is observed, which may indicate a change in the content of α-helices. With a further increase of temperature of the sample treatment, the observed changes were minimal.

The heating of MpOmp sample in solutions of both detergents in the studied temperature range did not lead to any major noticeable changes detected by fluorescence spectroscopy. The data obtained allow us to conclude that only an ionic detergent is capable to effect the conformational changes in the structure of the porin studied.
