Microtubule doublet (MTD) is the main skeleton of cilia/flagella. Many proteins, such as dyneins and radial spokes, bind to MTD, and generate or regulate force. While the structure of the reconstituted microtubule has been solved at atomic resolution, nature of the axonemal MTD is still unclear. There are a few hypotheses of the lattice arrangement of its α- and β-tubulins, but it has not been described how dyneins and radial spokes bind to MTD. In this study, we analyzed the three-dimensional structure of Tetrahymena MTD at ∼19 Å resolution by single particle cryo-electron microscopy. To identify α- and β-tubulins, we combined image analysis of MTD with specific kinesin decoration. This work reveals that α- and β-tubulins form a B-lattice arrangement in the entire MTD with a seam at the outer junction. We revealed the unique way in which inner arm dyneins, radial spokes, and proteins inside MTD bind and bridge protofilaments.

Cytoplasmic assembly of ciliary dyneins, a process known as preassembly, requires numerous non-dynein proteins, but the identities and functions of these proteins are not fully elucidated. Here, we show that the classical Chlamydomonas motility mutant pf23 is defective in the Chlamydomonas homolog of DYX1C1. The pf23 mutant has a 494 bp deletion in the DYX1C1 gene and expresses a shorter DYX1C1 protein in the cytoplasm. Structural analyses, using cryo-ET, reveal that pf23 axonemes lack most of the inner dynein arms. Spectral counting confirms that DYX1C1 is essential for the assembly of the majority of ciliary inner dynein arms (IDA) as well as a fraction of the outer dynein arms (ODA). A C-terminal truncation of DYX1C1 shows a reduction in a subset of these ciliary IDAs. Sucrose gradients of cytoplasmic extracts show that preassembled ciliary dyneins are reduced compared to wild-type, which suggests an important role in dynein complex stability. The role of PF23/DYX1C1 remains unknown, but we suggest that DYX1C1 could provide a scaffold for macromolecular assembly.

Background:Catestatin is emerging as a novel regulator of cardiovascular/metabolic functions. Results: We discovered a common amino acid substitution variant of catestatin that caused profound changes in plasma catecholamines, glucose, and lipid levels. Conclusion: Naturally occurring variants of catestatin peptide seem to alter the risk for metabolic syndrome. Significance: These findings provide new insights into the mechanism of metabolic diseases in humans.

Contractile injection systems (bacteriophage tails, type VI secretions system, R‐type pyocins, etc.) utilize a rigid tube/contractile sheath assembly for breaching the envelope of bacterial and eukaryotic cells. Among contractile injection systems, bacteriophages that infect Gram‐positive bacteria represent the least understood members. Here, we describe the structure of Listeria bacteriophage A511 tail in its pre‐ and post‐host attachment states (extended and contracted, respectively) using cryo‐electron microscopy, cryo‐electron tomography, and X‐ray crystallography. We show that the structure of the tube‐baseplate complex of A511 is similar to that of phage T4, but the A511 baseplate is decorated with different receptor‐binding proteins, which undergo a large structural transformation upon host attachment and switch the symmetry of the baseplate‐tail fiber assembly from threefold to sixfold. For the first time under native conditions, we show that contraction of the phage tail sheath assembly starts at the baseplate and propagates through the sheath in a domino‐like motion.