Mitochondria consist of two membranes and around thousand different proteins. Most mitochondrial proteins are encoded by the nuclear DNA, synthesized in the cytosol, and imported into and sorted within mitochondria with the aid of translocators in the mitochondrial membranes. Translocators function as a receptor for recognition of destination signals, provide a protein conducting channel, and drive vectorial translocation and unfolding of substrate mitochondrial proteins. This review provides an overview on the current understanding of the structure and functions of the TOM40 complex and TIM23 complex, two of the four major translocators in mitochondria.
The bacterial flagellar filament controls the swimming mode of bacteria by its polymorphic structural change. We investigated dynamics of the flagellar filament by massive molecular dynamic simulation and found that three types of inter-molecular interactions, permanent, sliding and switch interactions, play essential roles in the structural change. The polymorphic structure of the flagellar filament is thought to be due to energy frustration between intra- and inter-molecular interactions.
Previous kinetic investigations have suggested that the process of the specific complex formation goes through intermediate states called target searches or encounter complexes, and the presence of such intermediates greatly accelerates the overall process. However, current biophysics has not provided adequate physical pictures about such intermediates. We have developed new NMR methods that permit investigations of structural and dynamics aspects of the transient, low-population intermediates in protein-DNA or protein-protein association processes. The methods make use of paramagnetic relaxation enhancement (PRE) as a tool to amplify the information about the minor species.
Gastrulation is a crucial event at the early embryogenesis in animals. In vertebrates, gastrulation sets presumptive ectoderm, mesoderm, and endoderm cells in position. Furthermore, primary body axes were established through the gastrulation. Although precise analyses of gastrulation movement have revealed how to organize the body plan, many molecular mechanisms still remained to be clarified. Amphibian embryo, especially Xenopus laevis, lies on a lot of information that had been studied for the subject of gastrulation. This review outlines the movement of mesoderm cells in Xenopus, and discusses the role of a chemokine in cell migration during gastrulation.
The chemoreceptors of Escherichia coli cluster at a cell pole, a property which is critical for signaling. However, little is known about the mechanism of polar localization. Our recent study demonstrated that the aspartate chemoreceptor (Tar)-GFP fusion protein is inserted into lateral membrane regions and migrates to the pole. Unexpectedly, Tar-GFP was found to be arranged into a coil, which reflects a coil of the Sec protein translocation machinery. The Sec coil appeared distinct from the coil of MreB, an actin-like cytoskeletal protein. These findings shed new light on the spatial organization of membrane proteins in E. coli.
Due to thermal motion protein is always changing its three-dimensional structure. Characteristics of individual structures are usually hidden under temporal and ensemble averaging. A direct method to study individuals is to freeze thermal motion at low temperature and perform spectroscopy on individual proteins. This method has been applied to pigment-protein complex called light-harvesting 2 (LH2) complex from photosynthetic bacteria. In the fluorescence excitation spectrum of individual LH2 complexes taken at 1.5 K narrow peaks around 800 nm represent excitation of individual bacteriochlorophyll (BChl) a molecules while broad spectral feature around 860 nm reflects delocalized nature of excitation involving BChl a molecules arranged on a circle.