Active transport of macromolecules between the nucleus and the cytoplasm is mediated by transport receptors (carriers) that facilitate the passage of specific cargoes through the nuclear pore complexes. All of the nuclear transport pathways are based on a common principle: translocation across the nuclear pore appears to be reversible, and the directionality of transport depends on assembly of cargo-carrier complexes on one side of the nuclear envelope and disassembly of the transport complexes on the other side. This review highlights recent progress in understanding the structural basis of nuclear transport, especially in terms of CRM1-mediated nuclear export.
The formation of neuronal networks depends critically on the growth cone, a motile ameboid structure at the tip of elongating axon. Graded distributions of extracellular guidance cues attract or repel the growth cone by generating asymmetric cytosolic Ca2+ signals across the growth cone. We showed that the directional polarity of growth cone guidance is determined by the source of Ca2+ signals. We also demonstrated that, downstream of Ca2+ signals, asymmetric exocytosis and endocytosis drive growth cone attraction and repulsion, respectively. These findings provide a novel concept that polarized membrane trafficking acts as an instructive mechanism to spatially localize the steering apparatus such as cytoskeletal components and adhesion molecules.
Formin homology proteins (formins) play critical roles in the formation of actin stress fibers, the yeast actin cable and the cytokinetic contractile ring. Formins bind around the barbed end and processively elongate the actin filament (F-actin). However, it is unclear how and where in the cell formins form these actin-based structures. Here, we show the rotational movement of a mammalian formin mDia1 along the long-pitch helix of F-actin during processive elongation and depolymerization. From these properties, we postulate that helical rotation of formins may regulate actin assembly and filament stabilization during processive F-actin elongation.
Recent progress in the theory of molecular recognition in biomolecules is reviewed, which has been made based on the statistical mechanics of liquids or the 3D-RISM/RISM theory. The molecular recognition of a ligand by the protein is realized by the 3D-distribution functions: if one finds some conspicuous peaks in the distribution of a ligand inside protein, then the ligand is regarded as “recognized” by the protein. 3D-distribution functions can be obtained by means of 3D-RISM/RISM theory. Some biochemical processes are investigated, which are intimately related to the molecular recognition of small ligands such as water, ions, and carbon monoxide by a protein.