The popular model annelid Enchytraeus albidus is only one species in a complex of seashore white worms (Clitellata, Enchytraeidae)

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Structure of a Chaperone-Usher Pilus reveals the molecular basis of rod uncoiling

Types 1 and P pili are prototypical bacterial cell-surface appendages playing essential roles in mediating adhesion of bacteria to the urinary tract. These pili, assembled by the chaperone-usher pathway, are polymers of pilus subunits assembling into two parts: a thin, short tip fibrillum at the top, mounted on a long pilus rod. The rod adopts a helical quaternary structure and is thought to play essential roles: its formation may drive pilus extrusion by preventing backsliding of the nascent growing pilus within the secretion pore; the rod also has striking spring-like properties, being able to uncoil and recoil depending on the intensity of shear forces generated by urine flow. Here, we present an atomic model of the P pilus generated from a 3.8 Å resolution cryo-electron microscopy reconstruction. This structure provides the molecular basis for the rod’s remarkable mechanical properties and illuminates its role in pilus secretion

Cardiotonic bipyridine amrinone slows myosin-induced actin filament sliding at saturating [MgATP]

Previously reported effects of amrinone on skeletal muscle function suggest that the drug reduces the rate constant of myosin cross-bridge dissociation. We have used the in vitro motility assay to further elucidate the mechanism underlying this effect and to aid these studies a new, improved,. lament tracking software was developed in the Matlab(TM) environment. The experiments were carried out at 30degreesC using heavy meromyosin from fast rabbit muscle and rhodamine-phalloidin labeled actin. laments. A slowing effect of amrinone on. lament sliding velocity at 1 mM MgATP was observed at drug concentrations >0.3 mM. This effect showed signs of saturation at the highest drug concentrations (1-2 mM) that could be readily tested. The sliding velocity exhibited hyperbolic dependence on [ MgATP] with a V-max of 7.2 +/- 0.9 mum/s and a K-M of 0.18 +/- 0.02 mM. Amrinone (1 mM) reduced V-max by 32 +/- 5% (P < 0.01) and K-M by 42 &PLUSMN; 8% (P < 0.05; n = 4). These results are accounted for in the most straightforward way by a model where amrinone acts directly on the actomyosin system and reduces the rate constant of MgADP release. Such a well-defined effect on the myosin cross-bridge cycle makes the drug a potentially useful pharmacological tool for further studies of myosin function both in vitro and in the ordered. lament array of a living muscle fiber

Two species of Lumbricillus (Enchytraeidae, Annelida) new to Antarctica

The intertidal fauna of the Antarctic Peninsula has a relatively high species diversity, due to its warmer environment compared to other parts of Antarctica. Marine oligochaetes are, in general, one of the most diverse and ecologically important benthic organism groups, at least in the littoral zone. Antarctica has been one of the least studied areas with regard to oligochaete diversity. Here we report two&nbsp;Lumbricillus&nbsp;species (Lumbricillus antarcticus&nbsp;Stephenson, 1932 and&nbsp;Lumbricillus sejongensis&nbsp;sp. nov.) new to Antarctica, found in a tidal pool on the Barton Peninsula, King George Island. The diversity of this genus remains poorly known for Antarctica and the Subantarctic islands, and what we know is based on a few patchy studies