Application of Raman spectroscopy for the determination of proteins denaturation and amino acids decomposition temperature.

Raman spectroscopy was employed to study the thermal denaturation of three different proteins, bovine serum albumin (BSA), lysozyme, ovalbumin; and the decomposition temperature of three amino acids, l-glutamine, l-cysteine, and l-alanine, all of them as lyophilized powders. All the Raman bands observed in the spectra obtained were recorded and analyzed at preset heating temperatures. The results obtained for either protein denaturation temperature TD and amino acid decomposition temperatures TM-dc, were compared with those measured by differential scanning calorimetry (DSC). The DSC and Raman results were additionally corroborated with a thermogravimetric analysis (TGA) for the case of proteins. This exercise indicated almost complete coincidence in the determination of these transition temperatures between the three techniques, evidencing the applicability of Raman spectroscopy in the study of denaturation and decomposition temperatures of proteins and amino acids.

Equilibrium self-assembly of small RNA viruses.

We propose a description for the quasiequilibrium self-assembly of small, single-stranded (ss) RNA viruses whose capsid proteins (CPs) have flexible, positively charged, disordered tails that associate with the negatively charged RNA genome molecules. We describe the assembly of such viruses as the interplay between two coupled phase-transition-like events: the formation of the protein shell (the capsid) by CPs and the condensation of a large ss viral RNA molecule. Electrostatic repulsion between the CPs competes with attractive hydrophobic interactions and attractive interaction between neutralized RNA segments mediated by the tail groups. An assembly diagram is derived in terms of the strength of attractive interactions between CPs and between CPs and the RNA molecules. It is compared with the results of recent studies of viral assembly. We demonstrate that the conventional theory of self-assembly, which does describe the assembly of empty capsids, is in general not applicable to the self-assembly of RNA-encapsidating virions.