Curr. Biol

Chaperonins are double-ring protein assemblies with a central cavity that provides a sequestered environment for in vivo protein folding. Their reaction cycle is thought to consist of a nucleotide-regulated alternation between an open substrate-acceptor state and a closed folding-active state. The cavity of ATP-charged group I chaperonins, typified by Escherichia coil GroEL [1], is sealed off by a co-chaperonin, whereas group II chaperonins - the archaeal thermosome and eukaryotic TRIC/CCT [2] - possess a built in lid [3-5]. The mechanism of the lid's rearrangements requires clarification, as even in the absence of nucleotides, thermosomes of Thermoplama acidophilum appear open in vitrified ice [6] and dosed in crystals [4]. Here we analyze the conformation of the thermosome at each step of the ATPase cycle by small angle neutron scattering. The apo-chaperonin is open in solution, and ATP binding induces Its further expansion. Closure seems to occur during ATP hydrolysis and before phosphate release, and represents the rate limiting step of the cycle. The same closure can be triggered by the crystallization buffer. Thus, the allosteric regulation of group II chaperonins appears different from that of their group I counterparts. (C) 2000 Elsevier Science Ltd. All rights reserved. [References: 21

Combining skin and olfactory α-synuclein seed amplification assays (SAA)—towards biomarker-driven phenotyping in synucleinopathies

Seed amplification assays (SAA) are becoming commonly used in synucleinopathies to detect α-synuclein aggregates. Studies in Parkinson's disease (PD) and isolated REM-sleep behavior disorder (iRBD) have shown a considerably lower sensitivity in the olfactory epithelium than in CSF or skin. To get an insight into α-synuclein (α-syn) distribution within the nervous system and reasons for low sensitivity, we compared SAA assessment of nasal brushings and skin biopsies in PD (n = 27) and iRBD patients (n = 18) and unaffected controls (n = 30). α-syn misfolding was overall found less commonly in the olfactory epithelium than in the skin, which could be partially explained by the nasal brushing matrix exerting an inhibitory effect on aggregation. Importantly, the α-syn distribution was not uniform: there was a higher deposition of misfolded α-syn across all sampled tissues in the iRBD cohort compared to PD (supporting the notion of RBD as a marker of a more malignant subtype of synucleinopathy) and in a subgroup of PD patients, misfolded α-syn was detectable only in the olfactory epithelium, suggestive of the recently proposed brain-first PD subtype. Assaying α-syn of diverse origins, such as olfactory (part of the central nervous system) and skin (peripheral nervous system), could increase diagnostic accuracy and allow better stratification of patients