The Role of Junctophilin Proteins in Cellular Function

Junctophilins (JPHs) comprise a family of structural proteins that connect the plasma membrane to intracellular organelles such as the endo/sarcoplasmic reticulum. Tethering of these membrane structures results in the formation of highly organized subcellular junctions that play important signaling roles in all excitable cell types. There are four JPH isoforms, expressed primarily in muscle and neuronal cell types. Each JPH protein consists of 6 'membrane occupation and recognition nexus' (MORN) motifs, a joining region connecting these to another set of 2 MORN motifs, a putative alpha-helical region, a divergent region exhibiting low homology between JPH isoforms, and a carboxy-terminal transmembrane region anchoring into the ER/SR membrane. JPH isoforms play essential roles in developing and maintaining subcellular membrane junctions. Conversely, inherited mutations in JPH2 cause hypertrophic or dilated cardiomyopathy, while trinucleotide expansions in the JPH3 gene cause Huntington Disease-Like 2. Loss of JPH1 protein levels can cause skeletal myopathy, while loss of cardiac JPH2 levels causes heart failure and atrial fibrillation, among other disease. This review will provide a comprehensive overview of the JPH gene family, phylogeny, and evolutionary analysis of JPH genes and other MORN domain proteins. JPH biogenesis, membrane tethering, and binding partners will be discussed, as well as functional roles of JPH isoforms in excitable cells. Finally, potential roles of JPH isoform deficits in human disease pathogenesis will be reviewed.

Designing 3D Membrane Modules for Gas Separation Based on Hollow Fibers from Poly(4-methyl-1-pentene)

Designing hollow fiber (HF) membrane modules occupies one of the key positions in the development of efficient membrane processes for various purposes. In developing HF membrane modules, it is very important to have a uniform HF distribution and flow mixing in the shell side to significantly improve mass transfer and efficiency. This work suggests the application of different textile 3D HF structures (braided hoses and woven tape fabrics). The 3D structures consist of melt-spun, dense HFs based on poly(4-methyl-1-pentene) (PMP). Since the textile processing of HFs can damage the wall of the fiber or close the fiber bore, the membrane properties of the obtained structures are tested with a CO2/CH4 mixture in the temperature range of 0 to 40 °C. It is shown that HFs within the textile structure keep the same transport and separation characteristics compared to initial HFs. The mechanical properties of the PMP-based HFs allow their use in typical textile processes for the production of various membrane structures, even at a larger scale. PMP-based membranes can find application in separation processes, where other polymeric membranes are not stable. For example, they can be used for the separation of hydrocarbons or gas mixtures with volatile organic compounds.

A synthetic membrane shaper for controlled liposome deformation

Shape defines the structure and function of cellular membranes. In cell division, the cell membrane deforms into a dumbbell shape, while organelles such as the autophagosome exhibit stomatocyte shapes. Bottom-up in vitro reconstitution of protein machineries that stabilize or resolve the membrane necks in such deformed liposome structures is of considerable interest to characterize their function. Here we develop a DNA-nanotechnology-based approach that we call Synthetic Membrane Shaper (SMS), where cholesterol-linked DNA structures attach to the liposome membrane to reproducibly generate high yields of stomatocytes and dumbbells. In silico simulations confirm the shape-stabilizing role of the SMS. We show that the SMS is fully compatible with protein reconstitution by assembling bacterial divisome proteins (DynaminA, FtsZ:ZipA) at the catenoidal neck of these membrane structures. The SMS approach provides a general tool for studying protein binding to complex membrane geometries that will greatly benefit synthetic cell research.

Surface Measurement of a Large Inflatable Reflector in Cryogenic Vacuum

The metrology of membrane structures, especially inflatable, curved, optical surfaces, remains challenging. Internal pressure, mechanical membrane properties, and circumferential boundary conditions imbue highly dynamic slopes to the final optic surface. Here, we present our method and experimental results for measuring a 1 m inflatable reflector’s shape response to dynamic perturbations in a thermal vacuum chamber. Our method uses phase-measuring deflectometry to track shape change in response to pressure change, thermal gradient, and controlled puncture. We use an initial measurement as a virtual null reference, allowing us to compare 500 mm of measurable aperture of the concave f/2, 1-meter diameter inflatable optic. We built a custom deflectometer that attaches to the TVAC window to make full use of its clear aperture, with kinematic references behind the test article for calibration. Our method produces 500 × 500 pixel resolution 3D surface maps with a repeatability of 150 nm RMS within a cryogenic vacuum environment (T = 140 K, P = 0.11 Pa).

Cdc42 GTPase activating proteins Rga4 and Rga6 coordinate septum synthesis and membrane trafficking at the division plane during cytokinesis

Fission yeast cytokinesis is driven by simultaneous septum synthesis, membrane furrowing and actomyosin ring constriction. The septum consists of a primary septum flanked by secondary septa. First, delivery of the glucan synthase Bgs1 and membrane vesicles initiate primary septum synthesis and furrowing. Next, Bgs4 is delivered for secondary septum formation. It is unclear how septum synthesis is coordinated with membrane furrowing. Cdc42 promotes delivery of Bgs1 but not Bgs4. We find that after primary septum initiation, Cdc42 inactivators Rga4 and Rga6 localize to the division site. In rga4Δrga6Δ mutants Cdc42 activity is enhanced during late cytokinesis and cells take longer to separate. Electron micrographs of the division site in these mutants exhibit malformed septum with irregular membrane structures. These mutants have a larger division plane with enhanced Bgs1 delivery but fail to enhance accumulation of Bgs4 and several exocytic proteins. Additionally, these mutants show endocytic defects at the division site. This suggests that Cdc42 regulates only specific membrane trafficking events. Our data indicate that while active Cdc42 promotes primary septum synthesis, as cytokinesis progresses Rga4 and Rga6 localize to the division site to decrease Cdc42 activity. This couples specific membrane trafficking events with septum formation to allow proper septum morphology.

Tents: a paradigm of lightness and sustainability in vernacular architecture and in Frei Otto's work

PurposeThe aim of this paper is to explore the relationship between vernacular architecture and Frei Otto's work, searching for shared principles and specific singularities, and testing whether lightness and sustainability can be identified as a common goal.Design/methodology/approachThe study is focused on tents and yurts, as archetypal examples of traditional architecture, and membrane structures and gridshells, as two types of light structures developed by Frei Otto. A comparative analysis of their behavior, form, elements, types, materials and strength has been carried out.FindingsThe survey carried out shows that Frei Otto's innovative tents and gridshells were not based on form imitation of vernacular architecture, but rather on a thorough understanding of physical form-generating processes, driving specific materials to optimal form, like his experiments with soap film models to generate tensioned minimal surfaces or his experiments with hanging chain net models to generate compressive antifunicular lattice shells.Originality/valueThis paper highlights how Frei Otto's endeavor to get the maximum with the minimum, to achieve a lot from a little, is also a key target of lightness and sustainability, and an essential feature of vernacular architecture.