Both cell-cell and cell-extracellular matrix adhesion events accompany recruitment of several cytoplasmic proteins at the beneath of plasma membranes. These proteins contain adaptor proteins, scaffolding proteins, and linker proteins between actin cytoskeleton and adhesion molecules, as well as signaling proteins such as Rho GTPases, their regulators and effectors controlling the cell adhesion events and cytoskeleton rearrangement. Interactions of these cytoplasmic proteins with membranes and/or transmembrane proteins are critical for cell adhesion and signal transduction. The known modes of the interactions include non-covalent binding to phospholipids or to transmembrane proteins through several protein modules, in addition to covalent attachment of proteins to lipid moieties inserted in the membrane lipid bilayer. One such protein module is the FERM (4.1 and ERM) domain, which was originally found in the N-terminal regions of band 4.1 and ERM (ezrin/radixin/moesin) proteins. These proteins are known to cross-link the cytoskeletons to plasma membranes in the Rho signaling pathway. Interestingly, the FERM domain of ERM proteins interacts with phosphatidylinositol-4,5-bisphosphate (PIP2) in membranes and several proteins containing adhesion molecules such as ICAMs (intercellular adhesion molecules) and CD44 (a cell receptor protein of hyarulonic acid), scaffolding proteins such as NHERFs (Na + /H + ion exchanger regulatory factor), and GDI (guanine-nucleotide dissociation inhibitor) for Rho GTPases. I will describe the crystal structures of the radixin FERM domain bound to these binding partners and discuss the molecular mechanisms by which ERM proteins accomplish the multiple molecular recognition.
Advances in quantum structure science and technology have proceeded in a remarkable manner over the past few years. In addition to basic science issues, imminent applications are occurring in fields as varied as quantum computing and biological sensors and manipulation. It has been stated that nano-structures are able to provide the most perfect crystals, free of impurities, defects and strain. The positron (anti-particle of the electron) appears to be an exquisitely sensitive probe of the quality of nano-structure and in the case of semiconductors, the electronic structure. Electron-positron annihilation produces two collinear γ -rays of equal energy (0.511 MeV) in vacuum and in the rest frame. In a real material the γ rays are slightly momentum Doppler shifted due to the momentum of the electron with which the positron is annihilating. By measuring these Doppler shifts one obtains information about the electronic momentum density. Additionally, the lifetime of the positron in a material is dictated by the electron density in the vicinity of the positron. Data are presented from a variety of quantum systems with emphasis on our measurements on CdSe quantum dots. A model and theory in support of our measurements will also be presented. This model predicts the smearing of the electronic momentum density at the boundary of the Jones zone proportional to the widening of the band gap as the quantum dot size decreases. Keywords: QUANTUM STRUCTURES, POSITRON ANNIHILATION SPECTROSCOPY, ELECTRONIC STRUCTUREActa Cryst. (2002 The retinoblastoma tumor suppressor protein (pRb) regulates the cell cycle, sponsors differentiation and restrains apoptosis. Dysfunctional pRb is thought to be necessary for the development of most human malignancies. As many of the anti-tumorigenic properties of pRb are mediated by its regulation of the E2F transcription factors, we have determined the crystal structure of a fragment of E2F (residues 409-426) bound to pRb. It reveals how E2F acts as a structural sensor of pRb integrity and illuminates the role played by these two proteins in the regulation of apoptosis. We also show that the binding of E2F (409-426) The lethal form of human malaria is caused by the protozoal parasite Plasmodium falciparum, and may be responsible for 1.5 million deaths per year. The lack of an effective vaccine means that there is an urgent need for novel approaches to prophylaxis and treatment. One such approach is the development of drugs that interfere with P. Falciparum cell-cycle regulation. In eukaryotic organisms where it has been studied, cell proliferation is controlled by the action of cyclin dependent kinases (CDKs). Activity of these enzymes is in turn controlled by a network of regulatory interactions and covalent modifications. We are studying CDK-containing complexes of P. Falciparum in order a) to characterize the extent to which P. Falciparum follows previously identified structural paradigms of cell-cycle regulation, and b) to facilitate the structure-based design of specific P. Falciparum CDK inh...
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