美国加利福尼亚大学Andy LiWang和Carrie Partch研究组合作取得一项新突破。他们发现完整时钟的重建揭示了昼夜节律计时机制。该项研究成果发表在2021年10月8日出版的《科学》上。

他们报告了体外完整蓝藻生物钟的重建，包括中央振荡器、信号转导通路、下游转录因子和启动子 DNA。整个系统自动振荡并通过基于荧光的读数多天保持相位连贯，无需用户干预即可同时实时观察每个组件。他们确定了心律失常突变体中循环丢失的分子基础，并探索了蓝藻时钟计时的基本机制。他们发现 SasA，一种与时钟输出相关的昼夜节律传感器组氨酸激酶，直接与 KaiC 六聚体上的 KaiB 结合，以调节中央振荡器的周期和幅度。

SasA 使用结构模拟将 KaiB 的罕见折叠开关构象协同招募到 KaiC 六聚体，以形成夜间抑制复合物并增强振荡器的节律性，特别是在 KaiB 浓度有限的情况下。因此，扩展的体外时钟揭示了以前未知的蓝藻昼夜节律系统在可变蛋白质浓度下保持节奏和节律的机制。

据介绍，生物钟控制基因表达以提供本地时间的内部表示。

附：英文原文

Title: Reconstitution of an intact clock reveals mechanisms of circadian timekeeping

Author: Archana G. Chavan, Jeffrey A. Swan, Joel Heisler, Cigdem Sancar, Dustin C. Ernst, Mingxu Fang, Joseph G. Palacios, Rebecca K. Spangler, Clive R. Bagshaw, Sarvind Tripathi, Priya Crosby, Susan S. Golden, Carrie L. Partch, Andy LiWang

Issue&Volume: 2021-10-08

Abstract: Circadian clocks control gene expression to provide an internal representation of local time. We report reconstitution of a complete cyanobacterial circadian clock in vitro, including the central oscillator, signal transduction pathways, downstream transcription factor, and promoter DNA. The entire system oscillates autonomously and remains phase coherent for many days with a fluorescence-based readout that enables real-time observation of each component simultaneously without user intervention. We identified the molecular basis for loss of cycling in an arrhythmic mutant and explored fundamental mechanisms of timekeeping in the cyanobacterial clock. We find that SasA, a circadian sensor histidine kinase associated with clock output, engages directly with KaiB on the KaiC hexamer to regulate period and amplitude of the central oscillator. SasA uses structural mimicry to cooperatively recruit the rare, fold-switched conformation of KaiB to the KaiC hexamer to form the nighttime repressive complex and enhance rhythmicity of the oscillator, particularly under limiting concentrations of KaiB. Thus, the expanded in vitro clock reveals previously unknown mechanisms by which the circadian system of cyanobacteria maintains the pace and rhythmicity under variable protein concentrations.

DOI: abd4453

Source: https://www.science.org/doi/10.1126/science.abd4453