1SDA-01 Structure and function of SecDF, a membrane integrated protein translocation enhancing factor(1SDA Prof Berg's featured lecture and dancing harmonized motility machineries,Symposium,The 51th Annual Meeting of the Biophysical Society of Japan)

Abstract

The ERK MAP kinase plays a central role in the signaling cascades of cell growth. Here, we show that stochastic ERK activity pulses regulate cell proliferation rates in a cell density-dependent manner. A biosensor based on the principle of fluorescence resonance energy (FRET) revealed stochastic ERK activity pulses fired spontaneously or propagated from adjacent cells. Frequency, but not amplitude, of ERK activity pulses exhibited a bell-shaped response to the cell density and cell proliferation rates. Consistently, synthetic ERK activity pulses generated by a lightswitchable CRaf protein accelerated cell proliferation. Taken together, these findings reveal a role of the stochastic ERK activity pulses in cell proliferation. 1SCA-06 細胞内シグナル伝達経路の情報コーディング Information coding of cellular signaling networksShinya Kuroda, Shinsuke Uda (Biophys. Biochem., University of Tokyo) Cellular signaling network can be regarded as a communication channel in the framework of Shannon's information theory. We can measure the distribution of phosphorylation of ERK and CREB and expression of IEGs products at a cell population level. We found that information transmission was generally more robust than averaged signal intensity despite pharmacological perturbations, and information transmission through unperturbed signaling pathways compensatorily increased in many signaling pathways. We propose that cells use information entropy as information, so that messages can be robustly transmitted despite noise and variation in molecular activities between individual cells. Information coding will be discussed as a general property of cellular signaling. In bacteria, SecA, the translocation ATPase and SecYEG, the polypeptideconducting channel, play central roles in protein translocation across the cytoplasmic membrane. Membrane proteins SecDF, conserved throughout the bacterial kingdom, form a complex with SecYEG and are required for efficient protein export. Thus, it is important to elucidate mechanisms of the SecDF enhancement of translocation. We discuss structure and function of SecDF on the basis of the crystal structure of the T. thermophilus ortholog and structure-instructed biochemical analyses of the E. coli system including site-directed in vivo photo-crosslinking. Based on the results, we propose that SecDF functions as a cation-driven molecular motor to pull a translocating polypeptide from the SecYEG. The flagellar rod is a competent drive shaft that transmits torque through the hook to the filament to propel the bacterial locomotion. The distal part of the rod is a helical assembly of FlgG, which shows an obvious sequence similarity with the hook protein. However, the mechanical property of the rod and the hook is quite distinct; the hook is a flexible universal joint, and the rod is a rigid drive shaft. To elucidate the structural basis of the mechanical property of the rod, we crystallized a core fragment of FlgG (FlgG47-227) and solved the structure at 2.0 Å. On the basis of the high resolution X-ray structure and the density ...