Hidden conformations differentiate day and night in a circadian pacemaker

作者：Jeffrey A. Swan, Colby R. Sandate, Archana G. Chavan, Alfred M. Freeberg, Diana Etwaru, Dustin C. Ernst, Joseph G. Palacios, Susan S. Golden, Andy LiWang, Gabriel C. Lander, Carrie L. Partch · 发表于：bioRxiv (Cold Spring Harbor Laboratory) · 年份：2021 · DOI：10.1101/2021.09.14.460370 · 被引用次数：3 · 研究领域：Photosynthetic Processes and Mechanisms、Plant Molecular Biology Research、Mitochondrial Function and Pathology

Abstract The AAA+ protein KaiC is the central pacemaker for cyanobacterial circadian rhythms. Composed of two hexameric rings with tightly coupled activities, KaiC undergoes changes in autophosphorylation on its C-terminal (CII) domain that restrict binding of of clock proteins on its N-terminal (CI) domain to the evening. Here, we use cryo-electron microscopy to investigate how daytime and nighttime states of CII regulate KaiB binding to CI. We find that the CII hexamer is destabilized during the day but takes on a rigidified C 2 -symmetric state at night,concomitant with ring-ring compression. Residues at the CI-CII interface are required for phospho-dependent KaiB association, coupling ATPase activity on CI to cooperative KaiB recruitment. Together these studies reveal how daily changes in KaiC phosphorylation regulate cyanobacterial circadian rhythms. One-Sentence Summary Cryo-EM structures of KaiC in its day and night states reveal the structural basis for assembly of clock regulatory complexes.