Biology subjects

Plitzko, J. M.

Publications and source records attributed to Plitzko, J. M..

23 records · Page 2Linked to original sources

bioRxiv2020

Structural basis for VIPP1 oligomerization and maintenance of thylakoid membrane integrity

Vesicle-inducing protein in plastids (VIPP1) is essential for the biogenesis and maintenance of thylakoid membranes, which transform light into life. However, it is unknown how VIPP1 performs its vital membrane-shaping function. Here, we use cryo-electron microscopy to determine structures of cyanobacterial VIPP1 rings, revealing how VIPP1 monomers flex and interweave to form basket-like assemblies of different symmetries. Three VIPP1 monomers together coordinate a non-canonical nucleotide binding pocket that is required for VIPP1 oligomerization. Inside the rings lumen, amphipathic helices from each monomer align to form large hydrophobic columns, enabling VIPP1 to bind and curve membranes. In vivo point mutations in these hydrophobic surfaces cause extreme thylakoid swelling under high light, indicating an essential role of VIPP1 lipid binding in resisting stress-induced damage. Our study provides a structural basis for understanding how the oligomerization of VIPP1 drives the biogenesis of thylakoid membranes and protects these life-giving membranes from environmental stress.

plant biology↗

bioRxiv2019

Charting the native architecture of thylakoid membranes with single-molecule precision

Thylakoid membranes scaffold an assortment of large protein complexes that work together to harness the energy of light to produce oxygen, NADPH, and ATP. It has been a longstanding challenge to visualize how the intricate thylakoid network organizes these protein complexes to finely tune the photosynthetic reactions. Using cryo-electron tomography to analyze membrane surface topology, we have mapped the native molecular landscape of thylakoid membranes within green algae cells. Our tomograms provide insights into the molecular forces that drive thylakoid stacking and reveal that photosystems I and II are strictly segregated at the borders between appressed and non-appressed membrane domains. This new approach to charting thylakoid topology lays the foundation for dissecting photosynthetic regulation at the level of single protein complexes within the cell.

plant biology↗

bioRxiv2018

Structure of a hibernating 100S ribosome reveals an inactive conformation of the ribosomal protein S1

To survive under conditions of stress, such as nutrient deprivation, bacterial 70S ribosomes dimerize to form hibernating 100S particles1. In {gamma}-proteobacteria, such as Escherichia coli, 100S formation requires the ribosome modulation factor (RMF) and the hibernation promoting factor (HPF)2-4. Although structures of E. coli 100S particles have been reported5,6, the low resolution (18-38 [A]) prevented the mechanism of ribosome inactivation and dimerization to be fully elucidated. Here we present single particle cryo-electron microscopy structures of hibernating 70S and 100S particles isolated from stationary phase E. coli cells at 3.0-7.9 [A] resolution, respectively. Preferred orientation bias for the complete 100S particle was overcome using tilting during data collection. The structures reveal the binding sites for HPF and RMF as well as the unexpected presence of deacylated E-site tRNA and ribosomal protein S1 in the 100S particle. HPF interacts with the anticodon-stem-loop of the E-tRNA and occludes the binding site for the mRNA as well as A- and P-site tRNAs. RMF stabilizes a compact conformation of S1, which together sequester the anti-Shine-Dalgarno (SD) sequence of the 16S ribosomal RNA (rRNA), thereby inhibiting translation initiation. At the dimerization interface, S1 and S2 form intersubunit bridges with S3 and S4 and the C-terminus of S2 probes the mRNA entrance channel of the symmetry related particle, thus suggesting that only translationally inactive ribosomes are prone to dimerization. The back-to-back 100S dimerization mediated by HPF and RMF is distinct from that observed previously in Gram-positive bacteria7-10 and reveals a unique function for S1 in ribosome dimerization and inactivation, rather than its canonical role in facilitating translation initiation.

molecular biology↗

bioRxiv2018

Reconstitution of a flexible SYCP3-DNA fibre suggests a mechanism for SYCP3 coating of the meiotic chromosome axis

The synaptonemal complex (SC) keeps homologous chromosomes in close alignment during meiotic crossover. A hallmark of SC formation is the presence of its protein component SYCP3 on the chromosome axis. As SC assembly progresses, SYCP3 is deposited on both axes of the homologue pair, forming the lateral element (LE) in the tripartite structure of the mature SC. We have used cryo-electron tomography and atomic force microscopy to study the mechanism of assembly and DNA binding of the SYCP3 fibre. We find that the three-dimensional architecture of the fibre is built on a highly irregular arrangement of SYCP3 molecules displaying very limited local geometry. Interaction between SYCP3 molecules is driven by the intrinsically disordered tails of the protein, with no contact between the helical cores, resulting in a flexible fibre assembly. We demonstrate that the SYCP3 fibre can engage in extensive interactions with DNA, indicative of an efficient mechanism for incorporation of DNA within the fibre. Taken together, our findings suggest that, upon deposition on the chromosome axis, SYCP3 spreads by polymerising into a fibre that is fastened to the chromosome surface via DNA binding. The resulting layer of SYCP3 coating the chromosome axis might provide a structural basis for LE assembly in meiotic prophase.

biophysics↗

bioRxiv2017

In situ architecture of the algal nuclear pore complex

Nuclear pore complexes (NPCs) span the nuclear envelope and mediate nucleocytoplasmic exchange. They are a hallmark of eukaryotes and are deeply rooted in the evolutionary origin of cellular compartmentalization. NPCs have an elaborate architecture that has been well studied in vertebrates. Whether this architecture is unique or varies significantly in other eukaryotic kingdoms remains unknown, predominantly due to missing in situ structural data. Here, we report the architecture of the algal NPC from the early branching eukaryote Chlamydomonas reinhardtii and compare it to the human NPC. We find that the inner ring of the Chlamydomonas NPC has an unexpectedly large diameter, and the outer rings exhibit an asymmetric oligomeric state that is unprecedented compared to all previously proposed models of NPC architecture. Our study provides evidence that the NPC is subject to substantial structural variation between species. The divergent and conserved features of NPC architecture provide insights into the evolution of the nucleocytoplasmic transport machinery.

cell biology↗