We present the nuclear Overhauser effect-based structure determination of the Q41N variant of ubiquitin at 2500 bar, where the alternatively folded N2 state is 97% populated. This allows us to characterize the structure of the "pure" N2 state of ubiquitin. The N2 state shows a substantial change in the orientation of strand β5 compared to that of the normal folded N1 state, which matches the changes seen upon binding of ubiquitin to ubiquitin-activating enzyme E1. The recognition of E1 by ubiquitin is therefore best explained by conformational selection rather than induced-fit motion.
The circadian clock is an endogenous biological mechanism that generates autonomous daily cycles of physiological activity. The cyanobacterial circadian clock, which consists of three clock proteins, KaiA, KaiB, and KaiC, works as a clock oscillator by forming the KaiABC complex. We examined the structural changes of KaiB during incubation with both KaiA and KaiC by PELDOR method. The PELDOR is a well-established method to determine the distance between radicals with high accuracy. PELDOR results show that the inter-distance between the spin labels in KaiB was initially about 33.0 Å;, and changed after incubation for several hours. These results indicate structural changes of KaiB in the formation of KaiABC complex. 2P008 2.5 kbar におけるユビキチン高エネルギー状態の立体構造 解析 Solution structure of the "pure" high-energy state of ubiquitin:
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