Molecular mechanism of flagellar motor rotation arrest in bacterial zoospores of Actinoplanes missouriensis before germination.

Zoospores of the filamentous actinomycete Actinoplanes missouriensis swim vigorously using flagella and stop swimming to initiate germination in response to nutrient exposure. However, the molecular mechanisms underlying swimming cessation remain unknown. A protein (FtgA) of unknown function encoded by a chemotaxis gene cluster (che cluster-1) was found to be required for flagellar rotation arrest; the zoospores of ftgA-knockout mutants kept swimming awkwardly after germination. An ftgA-overexpressing strain exhibited a non-flagellated phenotype. Isolation of a suppressor strain from this strain and further in vivo experiments revealed that the extended N-terminal region of FliN, a component of the C-ring of the flagellar basal body, was involved in the function of FtgA; FliN-P101S canceled the flagellar rotation arrest by FtgA, as well as the negative effect of ftgA-overexpression on flagellation. Furthermore, bacterial two-hybrid assays suggested that FtgA interacted not only with the C-terminal core region of FliN but also with chemotaxis regulatory proteins CheA1 and CheW1-2, which are encoded by che cluster-1. We propose the following working model of motility regulation in A. missouriensis zoospores: the chemotaxis sensory complex initially captures FtgA to allow zoospores to swim and then releases FtgA to stop flagellar rotation (i.e., swimming) in response to external nutrient signals.

Photothermally Heated Asymmetric Thin Nanopores Suggest the Influence of Temperature on the Intermediate Conformational State of Cytochrome c in an Electric Field.

Nanopore sensing is a label-free single-molecule technique that enables the study of the dynamical structural properties of proteins. Here, we detect the translocation of cytochrome c (Cyt c) through an asymmetric thin nanopore with photothermal heating to evaluate the influence of temperature on Cyt c conformation during its translocation in an electric field. Before Cyt c translocates through an asymmetric thin SiNx nanopore, ∼1 ms trapping events occur due to electric field-induced denaturation. These trapping events were corroborated by a control analysis with a transmission electron microscopy-drilled pore and denaturant buffer. Cyt c translocation events exhibited markedly greater broad current blockade when the pores were photothermally heated. Collectively, our molecular dynamics simulation predicted that an increased temperature facilitates denaturation of the α-helical structure of Cyt c, resulting in greater blockade current during Cyt c trapping. Our photothermal heating method can be used to study the influence of temperature on protein conformation at the single-molecule level in a label-free manner.

Idiopathic tinnitus concomitant with eye closure.

OBJECTIVE: To describe 2 patients presenting with idiopathic tinnitus concomitant with eye closure. STUDY DESIGN: Clinical capsule report. SETTING: University hospital. PATIENTS: Two patients presented with intermittent tinnitus synchronous with eye closing or blinking. Otoscopic examination revealed inward movement of tympanic membranes concomitantly with eye blinking or eye closure in 1 patient. Neither patient had facial nerve disease or myoclonus. INTERVENTIONS: Compliance in impedance audiometry was recorded. RESULTS: Compliance in impedance audiometry was reduced during eye blinking and eye closure in both cases. The tinnitus was attributed to muscular tinnitus via stapedial muscle contraction during eye closure. CONCLUSION: These are the rare 2 reported patients presenting with idiopathic muscular tinnitus concomitant with eye closure. The reductive change of compliance in impedance audiometry during tinnitus coincident with eye closure is a feature of this form of tinnitus. We suggest evaluation of compliance change in impedance audiometry to be a key examination in patients with stapedial muscular tinnitus concomitant with eye closure.