Thermal shift assays (TSAs) are among the most commonly used biophysical approaches in drug discovery in both academic and industrial settings. However, the most common interpretation of the data generated by a TSA is purely qualitative, using only the change in melting temperature (ΔTm) as a metric. This has left many questions surrounding the interpretation of the data as well as whether the TSA truly correlates with other assays. TSAs also lack theoretical descriptions of the melt behavior of proteins in the presence of multiple ligands. Here we describe a novel simplified analytical framework based on "pseudoisothermal" models as well as exact thermodynamic descriptions of protein-ligand melt behavior rooted in changes in the entropy of melting. We show how the models are broad and independently applicable, in that they can describe the behavior of any macromolecule such as a protein or DNA and demonstrate good correlations with other techniques. These models are shown to give good descriptions of assay systems containing single or multiple ligands and can determine the mechanism of interaction. The models are derived from first principles, and the theoretical justification is discussed.

The decrease in plasticity that occurs in the central nervous system during postnatal development is accompanied by the appearance of perineuronal nets (PNNs) around the cell body and dendrites of many classes of neuron. These structures are composed of extracellular matrix molecules, such as chondroitin sulfate proteoglycans (CSPGs), hyaluronan (HA), tenascin-R, and link proteins. To elucidate the role played by neurons and glial cells in constructing PNNs, we studied the expression of PNN components in the adult rat cerebellum by immunohistochemistry and in situ hybridization. In the deep cerebellar nuclei, only large excitatory neurons were surrounded by nets, which contained the CSPGs aggrecan, neurocan, brevican, versican, and phosphacan, along with tenascin-R and HA. Whereas both net-bearing neurons and glial cells were the sources of CSPGs and tenascin-R, only the neurons expressed the mRNA for HA synthases (HASs), cartilage link protein, and link protein Bral2. In the cerebellar cortex, Golgi neurons possessed PNNs and also synthesized HASs, cartilage link protein, and Bral2 mRNAs. To see whether HA might link PNNs to the neuronal cell surface by binding to a receptor, we investigated the expression of the HA receptors CD44, RHAMM, and LYVE-1. No immunolabelling for HA receptors on the membrane of net-bearing neurons was found. We therefore propose that HASs, which can retain HA on the cell surface, may act as a link between PNNs and neurons. Thus, HAS and link proteins might be key molecules for PNN formation and stability.