Generation of somatic electromechanical force by outer hair cells may be influenced by prestin-CASK interaction at the basal junction with the Deiter's cell

The motor protein, prestin, situated in the basolateral plasma membrane of cochlear outer hair cells (OHCs), underlies the generation of somatic, voltage-driven mechanical force, the basis for the exquisite sensitivity, frequency selectivity and dynamic range of mammalian hearing. The molecular and structural basis of the ontogenetic development of this electromechanical force has remained elusive. The present study demonstrates that this force is significantly reduced when the immature subcellular distribution of prestin found along the entire plasma membrane persists into maturity, as has been described in previous studies under hypothyroidism. This observation suggests that cochlear amplification is critically dependent on the surface expression and distribution of prestin. Searching for proteins involved in organizing the subcellular localization of prestin to the basolateral plasma membrane, we identified cochlear expression of a novel truncated prestin splice isoform named prestin 9b (Slc26A5d) that contains a putative PDZ domain-binding motif. Using prestin 9b as the bait in a yeast two-hybrid assay, we identified a calcium/calmodulin-dependent serine protein kinase (CASK) as an interaction partner of prestin. Co-immunoprecipitation assays showed that CASK and prestin 9b can interact with full-length prestin. CASK was co-localized with prestin in a membrane domain where prestin-expressing OHC membrane abuts prestin-free OHC membrane, but was absent from this area for thyroid hormone deficiency. These findings suggest that CASK and the truncated prestin splice isoform contribute to confinement of prestin to the basolateral region of the plasma membrane. By means of such an interaction, the basal junction region between the OHC and its Deiter's cell may contribute to efficient generation of somatic electromechanical force.

High-speed atomic force microscopy: Structure and dynamics of single proteins

For surface analysis of biological molecules, atomic force microscopy (AFM) is an appealing technique combining data acquisition under physiological conditions, for example buffer solution, room temperature and ambient pressure, and high resolution. However, a key feature of life, dynamics, could not be assessed until recently because of the slowness of conventional AFM setups. Thus, for observing bio-molecular processes, the gain of image acquisition speed signifies a key progress. Here, we review the development and recent achievements using high-speed atomic force microscopy (HS-AFM). The HS-AFM is now the only technique to assess structure and dynamics of single molecules, revealing molecular motor action and diffusion dynamics. From this imaging data, watching molecules at work, novel and direct insights could be gained concerning the structure, dynamics and function relationship at the single bio-molecule level.

Benchmarking yeast two-hybrid systems using the interactions of bacterial motility proteins

Yeast two-hybrid screens often produce vastly non-overlapping interaction data when the screens are conducted in different laboratories, or use different vectors, strains, or reporter genes. Here we investigate the underlying reasons for such inconsistencies and compare the effect of seven different vectors and their yeast two-hybrid interactions. Genome-wide array screens with 49 motility-related baits from Treponema pallidum yielded 77 and 165 interactions with bait vectors pLP-GBKT7 and pAS1-LP, respectively, including 21 overlapping interactions. In addition, 90 motility-related proteins from Escherichia coli were tested in all pairwise combinations and yielded 140 interactions when tested with pGBKT7g/pGADT7g vectors but only 47 when tested with pDEST32/pDEST22. We discuss the factors that determine these effects, including copy number, the nature of the fusion protein, and species-specific differences that explain non-conserved interactions among species. The pDEST22/pDEST32 vectors produce a higher fraction of interactions that are conserved and that are biologically relevant when compared with the pGBKT7/pGADT7-related vectors, but the latter appear to be more sensitive and thus detect more interactions overall.

Historical hematology: May-Hegglin anomaly

May-Hegglin anomaly is a rare autosomal dominant platelet disorder characterized by thrombocytopenia, giant platelets, and unique leukocyte inclusion bodies. This disorder was first described by May, a German physician, in 1909, and was subsequently described by a Swiss physician, Hegglin, in 1945. The pathogenesis of the disorder had been unknown until recently, when mutations in the gene encoding for nonmuscle myosin heavy chain IIA (MYH9) were identified. Unique cytoplasmic inclusion bodies are aggregates of nonmuscle myosin heavy chain IIA, and are only present in granulocytes. It is not yet known why inclusion bodies are not present in platelets, monocytes, and lymphocytes, or how giant platelets are formed. Interestingly, MYH9 is also found to be responsible for several related disorders with macrothrombocytopenia and leukocytes inclusion, including Sebastian, Fechtner, and Epstein syndromes, which feature deafness, nephritis, and/or cataract. Current interest is centered upon the mechanisms by which a single mutation causes a variety of phenotypes.

NXF2 is involved in cytoplasmic mRNA dynamics through interactions with motor proteins

Tap/NXF1, the founding member of the evolutionarily conserved NXF (Nuclear RNA export Factor) family of proteins, is required for the nuclear export of bulk poly(A)+ RNAs. In mice, three additional NXF family genes (NXF2, NXF3, NXF7) have been identified and characterized to date. Cumulative data suggest that NXF family members play roles, not only in nuclear mRNA export, but also in various aspects of post-transcriptional mRNA metabolism. In order to better understand the functional role of NXF2, we searched for its binding partners by yeast two-hybrid screening and identified several cytoplasmic motor proteins, including KIF17. The interaction of NXF2 with KIF17, which was confirmed by GST pull-down and co-immunoprecipitation assays, is mediated by the N-terminal domain of NXF2, which is required for the punctate localization patterns in dendrites of primary neurons. We also found that the NXF2-containing dendritic granules, which were co-localized with KIF17, mRNA and Staufen1, a known component of neuronal mRNA granules, moved bidirectionally along dendrites in a microtubule-dependent manner. These results suggest that NXF2, a nucleo-cytoplasmic mRNA transporter, plays additional roles in the cytoplasmic localization of mRNAs through interactions with cytoplasmic motor proteins.

Evidence that focal adhesion complexes power bacterial gliding motility

The bacterium Myxococcus xanthus has two motility systems: S motility, which is powered by type IV pilus retraction, and A motility, which is powered by unknown mechanism(s). We found that A motility involved transient adhesion complexes that remained at fixed positions relative to the substratum as cells moved forward. Complexes assembled at leading cell poles and dispersed at the rear of the cells. When cells reversed direction, the A-motility clusters relocalized to the new leading poles together with S-motility proteins. The Frz chemosensory system coordinated the two motility systems. The dynamics of protein cluster localization suggest that intracellular motors and force transmission by dynamic focal adhesions can power bacterial motility.

The Vibrio motor proteins, MotX and MotY, are associated with the basal body of Na-driven flagella and required for stator formation

The four motor proteins PomA, PomB, MotX and MotY, which are believed to be stator proteins, are essential for motility by the Na(+)-driven flagella of Vibrio alginolyticus. When we purified the flagellar basal bodies, MotX and MotY were detected in the basal body, which is the supramolecular complex comprised of the rotor and the bushing, but PomA and PomB were not. By antibody labelling, MotX and MotY were detected around the LP ring. These results indicate that MotX and MotY associate with the basal body. The basal body had a new ring structure beneath the LP ring, which was named the T ring. This structure was changed or lost in the basal body from a DeltamotX or DeltamotY strain. The T ring probably comprises MotX and MotY. In the absence of MotX or MotY, we demonstrated that PomA and PomB were not localized to a cell pole. From the above results, we suggest that MotX and MotY of the T ring are involved in the incorporation and/or stabilization of the PomA/PomB complex in the motor.

The distribution of motor proteins in the muscles and flame cells of the Schistosoma mansoni miracidium and primary sporocyst

Schistosoma mansoni eggs, miracidia and primary sporocysts were labelled with phalloidin-rhodamine to visualize filamentous actin structures. Analysis of these forms by confocal fluorescence microscopy revealed the presence of previously well-defined circular and longitudinal muscle layers. Besides these muscular layers that sustain and provide motility to these parasite forms, we found in these 3 consecutive developmental stages of the parasite previously unidentified actin-rich tubular structures. In the 3 forms, 4 actin-rich tubules could be observed by optical sectioning underneath the well-developed muscle layers. The tubules appear in pairs, transversal to the length of the parasite, and located towards the extremities. By using an anti-flame cell specific antibody we confirmed that the tubules co-localize with flame cells and also determined that the tubule core is filled with microtubules. The additional presence of myosin in these tubules strongly suggests that they are contractile structures.