Proteasomal conformation controls unfolding ability.

The 26S proteasome is the macromolecular machine responsible for the bulk of protein degradation in eukaryotic cells. As it degrades a ubiquitinated protein, the proteasome transitions from a substrate-accepting conformation (s1) to a set of substrate-processing conformations (s3 like), each stabilized by different intramolecular contacts. Tools to study these conformational changes remain limited, and although several interactions have been proposed to be important for stabilizing the proteasome's various conformations, it has been difficult to test these directly under equilibrium conditions. Here, we describe a conformationally sensitive Förster resonance energy transfer assay, in which fluorescent proteins are fused to Sem1 and Rpn6, which are nearer each other in substrate-processing conformations than in the substrate-accepting conformation. Using this assay, we find that two sets of interactions, one involving Rpn5 and another involving Rpn2, are both important for stabilizing substrate-processing conformations. Mutations that disrupt these interactions both destabilize substrate-processing conformations relative to the substrate-accepting conformation and diminish the proteasome's ability to successfully unfold and degrade hard-to-unfold substrates, providing a link between the proteasome's conformational state and its unfolding ability.

Ubiquitin receptors are required for substrate-mediated activation of the proteasome's unfolding ability.

The ubiquitin-proteasome system (UPS) is responsible for the bulk of protein degradation in eukaryotic cells, but the factors that cause different substrates to be unfolded and degraded to different extents are still poorly understood. We previously showed that polyubiquitinated substrates were degraded with greater processivity (with a higher tendency to be unfolded and degraded than released) than ubiquitin-independent substrates. Thus, even though ubiquitin chains are removed before unfolding and degradation occur, they affect the unfolding of a protein domain. How do ubiquitin chains activate the proteasome's unfolding ability? We investigated the roles of the three intrinsic proteasomal ubiquitin receptors - Rpn1, Rpn10 and Rpn13 - in this activation. We find that these receptors are required for substrate-mediated activation of the proteasome's unfolding ability. Rpn13 plays the largest role, but there is also partial redundancy between receptors. The architecture of substrate ubiquitination determines which receptors are needed for maximal unfolding ability, and, in some cases, simultaneous engagement of ubiquitin by multiple receptors may be required. Our results suggest physical models for how ubiquitin receptors communicate with the proteasomal motor proteins.

Effect of once-daily fluticasone furoate/vilanterol on 24-hour pulmonary function in patients with chronic obstructive pulmonary disease: a randomized, three-way, incomplete block, crossover study.

BACKGROUND: Available inhaled corticosteroid/long-acting ß(2)-agonist combinations for chronic obstructive pulmonary disease (COPD) require twice-daily administration. The combination of fluticasone furoate (FF) and vilanterol (VI) FF/VI is being developed in a novel dry powder inhaler for the treatment of COPD and asthma with the potential for once-daily dosing. Results from Phase II studies have shown clinically and statistically significant improvements over placebo in trough (24-hour postdose) forced expiratory volume in 1 second (FEV(1)) after once-daily dosing with FF or VI (VI concurrently with an inhaled corticosteroid) in asthma and VI in COPD. OBJECTIVES: This Phase III, multicenter, randomized, double-blind, placebo-controlled study was designed based on guidance from drug regulators with the goal of evaluating the 24-hour spirometric effect of once-daily FF/VI in patients with COPD. METHODS: Patients (aged ≥40 years) who completed a 2-week placebo run-in period were randomized to 1 of 18 three-course sequences of placebo and 2 of 3 dose combinations of FF/VI (50/25 µg, 100/25 µg, and 200/25 µg), dosed once daily in the morning. Each 28-day treatment period was separated by a 2-week, single-blind, placebo washout period. The primary end point was time-adjusted (weighted mean) 0 to 24-hour FEV(1) (AUC) at the end of each 28-day treatment period (period days 28-29). Safety profile assessments included incidence of adverse events (AEs) (defined according to the Medical Dictionary for Regulatory Activities), 12-lead ECG outputs, vital signs (pulse rate, diastolic and systolic blood pressure) and clinical laboratory assessments (including fasting serum glucose and potassium) and 24-hour serum cortisol. The pharmacokinetics of FF and VI were assessed at the end of each 28-day treatment period with FF/VI. RESULTS: Eighty-seven patients were screened; 54 completed run-in and were randomized to double-blind treatment. The mean patient age was 57.9 years, and 46% were male. The majority of patients were current smokers (83%) and were receiving short-acting ß(2)-agonists within the 3 months before screening (63%). All 3 strengths of once-daily FF/VI demonstrated significantly higher 0 to 24-hour (period days 28-29) change from period baseline weighted mean FEV(1) than placebo: adjusted mean improvements from placebo in FEV(1) for FF/VI were 220 to 236 mL (all, P < 0.001). Improvements versus placebo in change from period baseline serial FEV(1) measures were observed at each time-point and with each strength of FF/VI over the 0 to 25-hour period (period days 28-29), indicating sustained bronchodilation. The overall incidence of on-treatment AEs was low (10%-12% with FF/VI; 4% with placebo); 2 serious AEs were reported during washout periods (1 AE after FF/VI 50/25 µg and 1 AE after placebo) but neither was considered treatment related. No serious AEs were reported during the treatment periods or during the follow-up period. No clinically or statistically significant differences from placebo were reported for serum glucose or potassium. No significant effects on vital signs, ECG, or 24-hour serial serum cortisol were reported. The extent of systemic exposure to FF and VI at steady state was low for all strengths of FF/VI. CONCLUSIONS: FF/VI inhaled once daily in the morning for 28 days produced significant improvements in pulmonary function with a prolonged (>24 hours') duration of action in this population of patients with COPD. The combination was well tolerated. ClinicalTrials.gov identifier: NCT01072149.