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    ON THE COVER
    Secretory vesicles containing MMP9-GFP near the plasma membrane of MCF-7 breast cancer cells. Overlay of TIRF MMP9-GFP image (green) and platinum replica TEM image (gray) of a MCF-7 cell plasma membrane sheet. Note the presence of other unlabeled membrane structures found on the MCF-7 cell membrane (e.g., actin filaments are visible all around the secretory vesicles). Image © Stephens et al., 2019. See https://doi.org/10.1085/jgp.201812299.

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ISSN 0022-1295
EISSN 1540-7748
In this Issue

Research News

JGP study describes the spatiotemporal dynamics of proteins and lipids involved in the exocytosis of the matrix metalloproteinase MMP-9 from breast cancer cells.

Commentary

Squire and Luther consider new evidence for a simple lattice structure in mammalian skeletal muscle.

Rudnick highlights a kinetic analysis of a bacterial Nramp transporter that focuses on how H+ gradients are coupled to metal transport.

Perks and Pierce consider a new study in worms showing that touch intensity is encoded by the quantal activity of mechanoreceptors.

Reviews

Twomey et al. examine recent structural and functional data that have provided insight into AMPA receptor modulation by TARPs.

Research Articles

KtrAB is a bacterial ion channel with a noncanonical selectivity filter. Consequently, it was assumed to be rather unselective for monovalent cations. Mikušević et al. show that in the presence of Na+, KtrAB very selectively translocates K+, which results from a high binding affinity and facilitated K+ gating.

Cochlear amplification is mediated by the outer hair cell of the organ of Corti. Santos-Sacchi et al. reveal that the cell possesses a voltage-dependent motile frequency response that differs from that of its voltage sensor/effector, the electromotile protein prestin, implying variable coupling between the two.

This paper describes the dynamics of proteins and lipids during exocytosis of MMP-9 from cancer cells in real time using fluorescence microscopy. Stephens et al. find that core exocytic proteins, accessory proteins, and lipids are involved at sites of secretory vesicle fusion.

Ma et al. studied the 3-D arrangement of thick filaments in skeletal muscle by x-ray diffraction and electron microscopy and found a correlation between thick filament lattice type (simple or superlattice) and fiber type (fast/slow). This suggests that lattice organization contributes to muscle functional properties.

An Nramp transition metal transporter performs metal uniport, proton uniport, and proton–metal cotransport. Transmembrane voltage and pH gradients govern the rates of these processes, largely through a conserved salt-bridge network in the transmembrane scaffold of the transporter’s LeuT fold.

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