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SummaryDivIVA from Bacillus subtilis is a bifunctional protein with distinct roles in cell division and sporulation. During vegetative growth, DivIVA regulates the activity of the MinCD complex, thus helping to direct cell division to the correct mid-cell position. DivIVA fulfils a quite different role during sporulation in B. subtilis when it directs the oriC region of the chromosome to the cell pole before asymmetric cell division. DivIVA is a 19.5 kDa protein with a large part of its structure predicted to form a tropomyosin-like a a a a -helical coiledcoil. Here, we present a model for the quaternary structure of DivIVA, based on cryonegative stain transmission electron microscopy images. The purified protein appears as an elongated particle with lateral expansions at both ends producing a form that resembles a 'doggy-bone'. The particle mass estimated from these images agrees with the value of 145 kDa measured by analytical ultracentrifugation suggesting 6-to 8-mers. These DivIVA oligomers serve as building blocks in the formation of higher order assemblies giving rise to strings, wires and, finally, twodimensional lattices in a time-dependent manner.

Viruses are naturally formed bionanoparticles ranging in size from about 20 to 150 nm. Remarkably, small viruses are composed of one single protein chain folding into a capsid structure with icosahedral symmetry. The icosahedron is built from 60 asymmetric units and is the largest closed shell in which every subunit is in an identical environment. It is characterized by 2-fold, 3-fold and 5-fold rotational symmetry axes. By superposition of different protein oligomerization domains onto the symmetry axes of an icosahedron, a nanoparticle with icosahedral symmetry can be designed. We have recently described such a design of peptide nanoparticles using coiled-coil protein oligomerization domains. Here we show that oligomerization motifs other than coiled-coils can be used to form nanoparticles by incorporating the globular foldon domain from fibritin with a trimeric -sheet conformation into the design. We expressed and purified 8 different peptides and performed refolding studies and biophysical characterization with analytical ultra centrifugation (AUC) and electron microscopy (EM). In the first design version we joined the foldon domain to the pentameric coiled-coil domain of COMP and varied the lengths of the linker sequences between the two domains. In this design we observed only smaller nanoparticles. When in the second design the foldon domain was extended with an additional trimeric coiled-coil domain as a combined trimerization domain that is linked to the COMP pentamer, we observed nanoparticles of sizes and molecular weights as would be expected for icosahedral symmetry. Viruses and virus-like particles (VLPs) are known for their ability to induce a strong humoral and hence antibody mediated immune response due to their repetitive antigen display. Peptide based nanoparticles have similar properties to VLPs, which are in clinical trials as a carrier in vaccination. Therefore, these peptide nanoparticles represent an alternative platform for subunit vaccine using the concept of repetitive antigen display.

BackgroundMitochondria are central to the metabolism of cells and participate in many regulatory and signaling events. They are looked upon as dynamic tubular networks. We showed recently that the Carboxy-Terminal Modulator Protein (CTMP) is a mitochondrial protein that may be released into the cytosol under apoptotic conditions.Methodology/Principal FindingsHere we report an unexpected function of CTMP in mitochondrial homeostasis. In this study, both full length CTMP, and a CTMP mutant refractory to N-terminal cleavage and leading to an immature protein promote clustering of spherical mitochondria, suggesting a role for CTMP in the fission process. Indeed, cellular depletion of CTMP led to accumulation of swollen and interconnected mitochondria, without affecting the mitochondrial fusion process. Importantly, in vivo results support the relevance of these findings, as mitochondria from livers of adult CTMP knockout mice had a similar phenotype to cells depleted of CTMP.Conclusions/SignificanceTogether, these results lead us to propose that CTMP has a major function in mitochondrial dynamics and could be involved in the regulation of mitochondrial functions.