Trimerization of the N-Terminal Tail of Zika Virus NS4A Protein: A Potential In Vitro Antiviral Screening Assay

The nonstructural (NS) protein NS4A in flaviviruses is a membrane protein that is critical for virulence, and, among other roles, it participates in membrane morphogenesis. In dengue virus (DENV), the NS4A hydrophilic N–terminal tail, together with the first transmembrane domain, is involved in both homo-oligomerization and hetero–oligomerization with NS4B. In both DENV and Zika virus (ZIKV), this N-terminal tail (residues 1–48) forms a random coil in solution but becomes mostly α-helical upon interaction with detergents or lipid membranes. Herein, we show that a peptide from ZIKV NS4A that spans residues 4–58, which includes most of the N–terminal tail and a third of its first transmembrane domain, forms homotrimers in the absence of detergents or liposomes. After interaction with the latter, α–helical content increases, consistent with binding. The oligomeric size of NS4A is not known, as it has only been reported in SDS gels. Therefore, we propose that full-length NS4A forms homotrimers mediated by this region, and that disruption of the oligomerization of peptide ZIKV NS4A 4–58 in solution can potentially constitute the basis for an in vitro assay to discover antivirals.

Subcellular tube guidance requires anchoring of the apical and basal actin cortices through late endosomes

The actin cytoskeleton participates in a range of cellular processes. It supports cell shape changes by propagating forces within cells and between cells and their environment. Terminal cells of the Drosophila respiratory system form a subcellular tube by invaginating their apical plasma membrane; cortical actin networks at the basal and apical plasma membranes are critical for proper morphogenesis. Basal actin affects apical membrane morphogenesis, and it is not known how the two separate actin pools communicate. We report here that actin assembles around vesicles of the late endocytic pathway, which are present in the growth cone of the cell, between the tip of the subcellular tube and the leading filopodia of the basal membrane. Actin organized at late endosomes extends towards both membrane compartments. Preventing proper actin nucleation at late endosomes disturbs the directionality of tube growth, uncoupling it from the direction of cell elongation. Severing actin in this area affects tube integrity. These findings demonstrate a role for the late endocytic pathway in organizing actin for proper cell morphogenesis, in addition to its known role in membrane and protein trafficking.

Coordinated organization of mitochondrial lamellar cristae and gain of COX function during mitochondrial maturation in Drosophila

Lamellar cristae organize with the gain of COX function during mitochondrial maturation. Cristae membrane morphogenesis and the acquisition of function are intricately associated during mitochondrial development.

The Caenorhabditis elegans Tubby homolog dynamically modulates olfactory cilia membrane morphogenesis and phospholipid composition

Plasticity in sensory signaling is partly mediated via regulated trafficking of signaling molecules to and from primary cilia. Tubby-related proteins regulate ciliary protein transport; however, their roles in remodeling cilia properties are not fully understood. We find that the C. elegans TUB-1 Tubby homolog regulates membrane morphogenesis and signaling protein transport in specialized sensory cilia. In particular, TUB-1 is essential for sensory signaling-dependent reshaping of olfactory cilia morphology. We show that compromised sensory signaling alters cilia membrane phosphoinositide composition via TUB-1-dependent trafficking of a PIP5 kinase. TUB-1 regulates localization of this lipid kinase at the cilia base in part via localization of the AP-2 adaptor complex subunit DPY-23. Our results describe new functions for Tubby proteins in the dynamic regulation of cilia membrane lipid composition, morphology, and signaling protein content, and suggest that this conserved family of proteins plays a critical role in mediating cilia structural and functional plasticity.

The C. elegans Tubby homolog dynamically modulates olfactory cilia membrane morphogenesis and phospholipid composition

ABSTRACTPlasticity in sensory signaling is partly mediated via regulated trafficking of signaling molecules to and from primary cilia. Tubby-related proteins regulate ciliary protein transport; however, their roles in remodeling of cilia properties are not fully understood. We find that the C. elegans TUB-1 Tubby homolog regulates membrane morphogenesis and signaling protein transport in specialized sensory cilia. In particular, TUB-1 is essential for sensory signaling-dependent reshaping of olfactory cilia morphology. We show that compromised sensory signaling alters cilia membrane phosphoinositide composition via TUB-1-dependent trafficking of a PIP5 kinase. TUB-1 regulates localization of this lipid kinase at the cilia base in part via localization of the AP-2 adaptor complex subunit DPY-23. Our results describe new functions for Tubby proteins in the dynamic regulation of cilia membrane lipid composition, morphology, and signaling protein content, and suggest that this conserved family of proteins plays a critical role in mediating cilia structural and functional plasticity.

Mitochondrial cristae biogenesis coordinates with ETC complex IV assembly during Drosophila maturation

Mitochondrial cristae contain electron transport chain (ETC) complexes and are distinct from the inner boundary membrane (IBM) in both protein composition and function. While many details of mitochondrial membrane structure are known, the processes governing cristae biogenesis, including the organization of lipid membranes and assembly of proteins encoded by both nuclear and mitochondrial DNA, remain obscure. We followed cristae biogenesis in situ upon Drosophila eclosion using serial-section electron tomography and revealed that the morphogenesis of lamellar cristae coordinates with ETC complex IV assembly. The membrane morphogenesis and gain-of-function were intricately co-evolved during cristae biogenesis. Marf-knockdown flies formed lamellar cristae containing ATP synthase and functional COX. However, OPA1-knockdown flies showed impaired cristae biogenesis. Overall, this study revealed the multilevel coordination of protein-coupled membrane morphogenesis in building functional cristae.