Torque-speed relationship of the Na+-driven flagellar motor of Vibrio alginolyticus

The torque-speed relationship of the Na(+)-driven flagellar motor of Vibrio alginolyticus was investigated. The rotation rate of the motor was measured by following the position of a bead, attached to a flagellar filament, using optical nanometry. In the presence of 50mM NaCl, the generated torque was relatively constant ( approximately 3800pNnm) at lower speeds (speeds up to approximately 300Hz) and then decreased steeply, similar to the H(+)-driven flagellar motor of Escherichia coli. When the external NaCl concentration was varied, the generated torque of the flagellar motor was changed over a wide range of speeds. This result could be reproduced using a simple kinetic model, which takes into consideration the association and dissociation of Na(+) onto the motor. These results imply that for a complete understanding of the mechanism of flagellar rotation it is essential to consider both the electrochemical gradient and the absolute concentration of the coupling ion.     

In vitro differentiation from naive to mature E-selectin binding CD4 T cells: acquisition of skin-homing properties occurs independently of cutaneous lymphocyte antigen expression

We previously showed that skin-homing CD4 T cells in peripheral blood can be subdivided into three populations on the basis of the expression pattern of the cutaneous lymphocyte Ag (CLA) and fucosyltransferase VII (FucT-VII): FucT-VII(+)CLA(-), FucT-VII(+)CLA(+), and FucT-VII(-)CLA(+). In view of the known late appearance of CLA during T cell differentiation, T cells programmed to attain skin-homing properties may start to generate E-selectin-binding epitopes at early stages of differentiation before induction of CLA expression. To this end, the in vitro differentiation from naive to CLA(+) memory T cells was followed after activation with anti-CD3 mAb. Here we demonstrate that naive skin-homing CD4 T cell precursors undergo a linear differentiation process from the FucT-VII(+)CLA(-) phenotype to the FucT-VII(+)CLA(+) phenotype and eventually to the FucT-VII(-)CLA(+) phenotype. The appearance of the FucT-VII(+)CLA(-) subset coincided with or could be immediately followed by the generation of E-selectin binding epitopes, and even after E-selectin-binding epitopes were no longer detectable, CLA remained expressed for prolonged periods of time, suggesting that induction of functional E-selectin ligands depends primarily on the expression of FucT-VII, but not CLA. Immunofluorescence and confocal microscopy studies of these T cells confirm that most E-selectin ligands were found independently of CLA expression.     

A kinetic mechanism for the fast movement of Chara myosin

Endoplasmic streaming of characean cells of Nitella or Chara is known to be in the range 30-100 microm/second. The Chara myosin extracted from the cells and fixed onto a glass surface was found to move muscle actin filaments at a velocity of 60 microm/second. This is ten times faster than that of skeletal muscle myosin (myosin II). In this study, the displacement caused by single Chara myosin molecules was measured using optical trapping nanometry. The step size of Chara myosin was approximately 19nm. This step size is longer than that of skeletal muscle myosin but shorter than that of myosin V. The dwell time of the steps was relatively long, and this most likely resulted from two rate-limiting steps, the dissociation of ADP and the binding of ATP. The rate of ADP release from Chara myosin after the completion of the force-generation step was similar to that of myosin V, but was considerably slower than that of skeletal muscle myosin. The 19nm step size and the dwell time obtained could not explain the fast movement. The fast movement could be explained by the load-dependent release of ADP. As the load imposed on the myosin decreased, the rate of ADP release increased. We propose that the interaction of Chara myosin with an actin filament resulted in a negative load being imposed on other myosin molecules interacting with the same actin filament. This resulted in an accelerated release of ADP and the fast sliding movement.     

Nerve growth factor-induced glutamate release is via p75 receptor,ceramide, and Ca(2+) from ryanodine receptor in developing cerebellar neurons

Very little is known about the contribution of a low affinity neurotrophin receptor, p75, to neurotransmitter release. Here we show that nerve growth factor (NGF) induced a rapid release of glutamate and an increase of Ca2+ in cerebellar neurons through a p75-dependent pathway. The NGF-induced release occurred even in the presence of the Trk inhibitor K252a. The release caused by NGF but not brain-derived neurotrophic factor was enhanced in neurons overexpressing p75. Further, after transfection of p75-small interfering RNA, which down-regulated the endogenous p75 expression, the NGF-induced release was inhibited, suggesting that the NGF-induced glutamate release was through p75. We found that the NGF-increased Ca2+ was derived from the ryanodine-sensitive Ca2+ receptor and that the NGF-increased Ca2+ was essential for the NGF-induced glutamate release. Furthermore, scyphostatin, a sphingomyelinase inhibitor, blocked the NGF-dependent Ca2+ increase and glutamate release, suggesting that a ceramide produced by sphingomyelinase was required for the NGF-stimulated Ca2+ increase and glutamate release. This action of NGF only occurred in developing neurons whereas the brain-derived neurotrophic factor-mediated Ca2+ increase and glutamate release was observed at the mature neuronal stage. Thus, we demonstrate that NGF-mediated neurotransmitter release via the p75-dependent pathway has an important role in developing neurons.     

Complementation of Escherichia coli ubiF mutation by Caenorhabditis elegans CLK-1, a product of the longevity gene of the nematode worm

Caenorhabditis elegans CLK-1 was identified from long-lived mutant worms, and is believed to be involved in ubiquinone biosynthesis. The protein belongs to the eukaryotic CLK-1/Coq7p family, which is also similar to the bacterial Coq7 family, that hydroxylates demethoxyubiquinone, resulting in the formation of hydroxyubiquinone, a precursor of ubiquinone. In Escherichia coli, the corresponding reaction is catalyzed by UbiF, a member of a distinct class of hydroxylase. Although previous studies suggested that the eukaryotic CLK-1/Coq7 family is a hydroxylase of demethoxyubiquinone, there was no direct evidence to show the enzymatic activity of the eukaryotic CLK-1/Coq7 family. Here we show that the plasmid encoding C. elegans CLK-1 supported aerobic respiration on a non-fermentable carbon source of E. coli ubiF mutant strain and rescued the ability to synthesize ubiquinone, suggesting that the eukaryotic CLK-1/Coq7p family could function as bacterial UbiF.