Small angle neutron scattering analysis of thermal stability of 23S rRNA and the intact 50S subunits of Sulfolobus solfataricus.

The ribosomes of the extremely thermophilic archaebacterium, Sulfolobus solfataricus, are very resistant to thermal denaturation (optimal growth temperature 87 degrees C), remaining essentially intact up to above 90 degrees C. However, the separate ribosomal components (rRNA and r-proteins) are less thermally stable than the ribosome as a whole, indicating that the mode of interaction of all of the components within the ribonucleoprotein particle play an essential role in determining thermal stability. To get some insight into the structural features of the thermophilic ribosome, we performed small angle neutron scattering (SANS) measurements at various temperatures on Sulfolobus solfataricus intact large ribosomal subunits (50S) and deproteinated large ribosomal subunit RNA (23S). Even if the scattering profiles suggest the presence of supramolecular aggregates in all of the samples and at all of the investigated temperatures, the measured form factors indicated for both samples that, at temperatures above 70 degrees C, the suspended particles underwent a structural rearrangement. This finding is likely to reflect single particles' properties, since S. solfataricus ribosomes are known to be biologically activated only above 60 degrees C, and there are indications that such activation requires a conformational rearrangement of the particle. A remarkable superimposition of the percentage variation of the volume from neutron scattering and of the absorbency increment with respect to temperature supports this view.