The thermodynamic hypothesis of protein folding, known as the “Anfinsen’s dogma”, states that the native structure of a protein represents a free energy minimum determined by the amino acid sequence. However, inconsistent with the dogma, globular proteins can misfold to form amyloid fibrils. Here, we present a general concept for the link between folding and misfolding. We show that folding and amyloid formation are separated by the supersaturation barrier of a protein. Its breakdown is required to shift the protein to the amyloid pathway. Thus, the breakdown of supersaturation links the Anfinsen’s intramolecular folding universe and the intermolecular misfolding universe.

G protein-coupled receptors (GPCRs) constitute one of the largest superfamily of proteins in the human genome. Since GPCRs are major drug targets, a pharmacological evaluation of compounds on a GPCR is an important process in drug discovery. Here, we review the past trends of the in cell single-molecule measurement of GPCRs, many of which were focused on dimerization of GPCRs. Then, we introduce our recent study regarding the drug evaluation based on a general feature of a diffusion-function relationship of GPCRs. We also discuss the future applicability of the present study in pharmacology and drug screening.

While irreversible aggregation or amyloid formation of denatured proteins is well known and studied in detail, the reversible oligomerization (RO) states of some monomeric proteins at high temperature have been recently discovered by DSC analysis. In this article, the RO states of horse cytochrome c, a simplified BPTI variants with hydrophobic peptide tag at the C-terminus end, the envelope protein domain 3 from dengue 4 virus, and the third PDZ domain of the PSD95 neuronal protein were reviewed. The hydrophobic interaction in the denatured state is indicated to be the main factor to stabilize RO state, and the significance of RO was discussed as a key process for the kinetics of the irreversible amyloid formation.

The optogenetic method allows us to manipulate cellular activity with high spatiotemporal resolution. The most widely used optogenetic tool is channelrhodopsin-2 that can be utilized to control neuronal activity at the cellular level. However, optogenetic tools capable of inducing synaptic plasticity at the level of single synapses (spines) have been lacking. We recently developed a photoactivatable CaMKII by fusing a light-sensitive domain, LOV2, to CaMKIIα. Combining two-photon excitation, we successfully activated photoactivatable CaMKII in single spines and induced long-term potentiation (LTP) in hippocampal neurons. The manipulation of LTP at the single spines (we call it “local optogenetics”) will find many applications in neuroscience and other fields.