CCDC32 collaborates with the membrane to assemble the AP-2 clathrin adaptor complex.

Cells have evolved a variety of assembly chaperones to aid in the difficult process of forming macromolecular complexes in a crowded cytoplasm. Assembly of adaptor protein complex 2 (AP-2), the primary cargo adaptor in clathrin-mediated endocytosis, is regulated by the chaperones AAGAB and CCDC32, whose deletion causes loss of all AP-2 subunits . AAGAB and CCDC32 are thought to act sequentially to assemble the AP-2 tetramer from its constituent heterodimers.

Oligomer-based functions of mitochondrial porin.

Porin, or the voltage-dependent anion channel (VDAC), is a primary β-barrel channel in the mitochondrial outer membrane. It transports small metabolites and ions through its β-barrel pore and plays key roles in apoptosis and inflammatory response. Here we report the cryo-electron microscopy structure of yeast porin (Por1) in its hexameric form at 3.

Cryo-EM of wild-type and mutant PMEL amyloid cores reveals structural mechanism of pigment dispersion syndrome.

PMEL amyloids serve as essential scaffolds for melanin deposition in melanosomes, playing a crucial role in pigmentation. Despite their importance, the high-resolution structure of PMEL amyloids has remained unresolved. Using cryo-electron microscopy, we determine near-atomic resolution structures of wild-type PMEL amyloid core, revealing two distinct polymorphic forms with structural features.

Tension-induced suppression of allosteric conformational changes coordinates kinesin-1 stepping.

Kinesin-1 walks along microtubules by alternating ATP hydrolysis and movement of its two motor domains ("head"). The detached head preferentially binds to the forward tubulin-binding site after ATP binds to the microtubule-bound head, but the mechanism preventing premature microtubule binding while the partner head awaits ATP remains unknown. Here, we examined the role of the neck linker, the segment connecting two heads, in this mechanism.

Cryo-EM Structures of Native Chromatin Units From Human Cells.

In eukaryotic cells, genomic DNA is compacted by nucleosomes, as basic repeating units, into chromatin. The nucleosome arrangement in chromatin fibers could be an important determinant for chromatin folding, by which genomic DNA is regulated in the nucleus. To study the structures of chromatin units in cells, we have established a method for the structural analysis of native mono- and poly-nucleosomes prepared from HeLa cells.

Dimerization of GAS2 mediates crosslinking of microtubules and F-actin.

The spectraplakin family protein GAS2 was originally identified as a growth arrest-specific protein, and recent studies have revealed its involvement in multiple cellular processes. Its dual interaction with actin filaments and microtubules highlights its essential role in cytoskeletal organization, such as cell division, apoptosis, and possibly tumorigenesis. However, the structural basis of cytoskeletal dynamics regulation by GAS2 remains unclear.

Structure and function of FAP47 in the central pair apparatus of Chlamydomonas flagella.

Motile cilia have a so-called "9 + 2" structure, which consists of nine doublet microtubules and a central pair apparatus. The central pair apparatus (CA) is thought to interact mechanically with radial spokes and to control the flagellar beating. Recently, the components of the CA have been identified by proteomic and genomic analyses.

Calaxin is a key factor for calcium-dependent waveform control in zebrafish sperm.

Calcium is critical for regulating the waveform of motile cilia and flagella. Calaxin is currently the only known molecule involved in the calcium-dependent regulation in ascidians. We have recently shown that Calaxin stabilizes outer arm dynein (OAD), and the knockout of Calaxin results in primary ciliary dyskinesia phenotypes in vertebrates.

The role of the C-terminal tail region as a plug to regulate XKR8 lipid scramblase.

XK-related 8 (XKR8), in complex with the transmembrane glycoprotein basigin, functions as a phospholipid scramblase activated by the caspase-mediated cleavage or phosphorylation of its C-terminal tail. It carries a putative phospholipid translocation path of multiple hydrophobic and charged residues in the transmembrane region. It also has a crucial tryptophan at the exoplasmic end of the path that regulates its scrambling activity.

Cryo-EM elucidates the uroplakin complex structure within liquid-crystalline lipids in the porcine urothelial membrane.

The urothelium, a distinct epithelial tissue lining the urinary tract, serves as an essential component in preserving urinary tract integrity and thwarting infections. The asymmetric unit membrane (AUM), primarily composed of the uroplakin complex, constitutes a critical permeability barrier in fulfilling this role. However, the molecular architectures of both the AUM and the uroplakin complex have remained enigmatic due to the paucity of high-resolution structural data.

Cryo-EM structures of human zinc transporter ZnT7 reveal the mechanism of Zn uptake into the Golgi apparatus.

Zinc ions (Zn) are vital to most cells, with the intracellular concentrations of Zn being tightly regulated by multiple zinc transporters located at the plasma and organelle membranes. We herein present the 2.2-3.

α- and β-tubulin C-terminal tails with distinct modifications are crucial for ciliary motility and assembly.

α- and β-tubulin have an unstructured glutamate-rich region at their C-terminal tails (CTTs). The function of this region in cilia and flagella is still unclear, except that glutamates in CTTs act as the sites for post-translational modifications that affect ciliary motility. The unicellular alga Chlamydomonas possesses only two α-tubulin and two β-tubulin genes, each pair encoding an identical protein.

Unveiling Liquid-Crystalline Lipids in the Urothelial Membrane through Cryo-EM.

The urothelium, a distinct epithelial tissue lining the urinary tract, serves as an essential component in preserving urinary tract integrity and thwarting infections. The asymmetric unit membrane (AUM), primarily composed of the uroplakin complex, constitutes a critical permeability barrier in fulfilling this role. However, the molecular architectures of both the AUM and the uroplakin complex have remained enigmatic due to the paucity of high-resolution structural data.

Unveiling Liquid-Crystalline Lipids in the Urothelial Membrane through Cryo-EM.

The urothelium, a distinct epithelial tissue lining the urinary tract, serves as an essential component in preserving urinary tract integrity and thwarting infections. The asymmetric unit membrane (AUM), primarily composed of the uroplakin complex, constitutes a critical permeability barrier in fulfilling this role. However, the molecular architectures of both the AUM and the uroplakin complex have remained enigmatic due to the paucity of high-resolution structural data.

ATP-Responsive Nanoparticles Covered with Biomolecular Machine "Chaperonin GroEL".

Herein, we report an ATP-responsive nanoparticle ( NP) whose surface is fully covered with the biomolecular machine "chaperonin protein GroEL". NP was synthesized by DNA hybridization between a gold NP with DNA strands on its surface and GroEL carrying complementary DNA strands at its apical domains. The unique structure of NP was visualized by transmission electron microscopy including under cryogenic conditions.

Calaxin stabilizes the docking of outer arm dyneins onto ciliary doublet microtubule in vertebrates.

Outer arm dynein (OAD) is the main force generator of ciliary beating. Although OAD loss is the most frequent cause of human primary ciliary dyskinesia, the docking mechanism of OAD onto the ciliary doublet microtubule (DMT) remains elusive in vertebrates. Here, we analyzed the functions of Calaxin/Efcab1 and Armc4, the two of five components of vertebrate OAD-DC (docking complex), using zebrafish spermatozoa and cryo-electron tomography.

Bioconjugation of Au Nanocluster to Monoclonal Antibody at Tryptophan.

We report the first bioconjugation of Au nanocluster to a monoclonal antibody at scarcely exposed tryptophan (Trp) residues toward the development of high-resolution probes for cryogenic electron microscopy (cryo-EM) and tomography (cryo-ET). To achieve this, we improved the Trp-selective bioconjugation using hydroxylamine (ABNOH) reagents instead of previously developed -oxyl radicals (ABNO). This new protocol allowed for the application of Trp-selective bioconjugation to acid-sensitive proteins such as antibodies.

Cryo-EM structures of human SPCA1a reveal the mechanism of Ca/Mn transport into the Golgi apparatus.

Secretory pathway Ca/Mn ATPase 1 (SPCA1) actively transports cytosolic Ca and Mn into the Golgi lumen, playing a crucial role in cellular calcium and manganese homeostasis. Detrimental mutations of the gene encoding SPCA1 cause Hailey-Hailey disease. Here, using nanobody/megabody technologies, we determined cryo-electron microscopy structures of human SPCA1a in the ATP and Ca/Mn-bound (E1-ATP) state and the metal-free phosphorylated (E2P) state at 3.

The association of ODF4 with AK1 and AK2 in mice is essential for fertility through its contribution to flagellar shape.

Normal sperm flagellar shape and movement are essential for fertilization. The integral protein outer dense fiber 4 (ODF4) localizes to ODFs, but its function remains unclear. Adenylate kinase (AK) is a phosphotransferase that catalyzes the interconversion and controls the concentration equilibrium of adenine nucleotides.

A multipoint guidance mechanism for β-barrel folding on the SAM complex.

Mitochondrial β-barrel proteins are essential for the transport of metabolites, ions and proteins. The sorting and assembly machinery (SAM) mediates their folding and membrane insertion. We report the cryo-electron microscopy structure of the yeast SAM complex carrying an early eukaryotic β-barrel folding intermediate.

Multiple sub-state structures of SERCA2b reveal conformational overlap at transition steps during the catalytic cycle.

Sarco/endoplasmic reticulum Ca ATPase (SERCA) pumps Ca into the endoplasmic reticulum (ER). Herein, we present cryo-electron microscopy (EM) structures of three intermediates of SERCA2b: Ca-bound phosphorylated (E1P·2Ca) and Ca-unbound dephosphorylated (E2·Pi) intermediates and another between the E2P and E2·Pi states. Our cryo-EM analysis demonstrates that the E1P·2Ca state exists in low abundance and preferentially transitions to an E2P-like structure by releasing Ca and that the Ca release gate subsequently undergoes stepwise closure during the dephosphorylation processes.

Parallel cryo electron tomography on in situ lamellae.

In situ cryo electron tomography of cryo focused ion beam milled samples has emerged in recent years as a powerful technique for structural studies of macromolecular complexes in their native cellular environment. However, the possibilities for recording tomographic tilt series in a high-throughput manner are limited, in part by the lamella-shaped samples. Here we utilize a geometrical sample model and optical image shift to record tens of tilt series in parallel, thereby saving time and gaining access to sample areas conventionally used for tracking specimen movement.