Structural mechanism of proton conduction in otopetrin proton channel.

The otopetrin (OTOP) proteins were recently characterized as extracellular proton-activated proton channels. Several recent OTOP channel structures demonstrated that the channels form a dimer with each subunit adopting a double-barrel architecture. However, the structural mechanisms underlying some basic functional properties of the OTOP channels remain unresolved, including extracellular pH activation, proton conducting pathway, and rapid desensitization.

TRPML1 gating modulation by allosteric mutations and lipids.

Transient Receptor Potential Mucolipin 1 (TRPML1) is a lysosomal cation channel whose loss-of-function mutations directly cause the lysosomal storage disorder mucolipidosis type IV (MLIV). TRPML1 can be allosterically regulated by various ligands including natural lipids and small synthetic molecules and the channel undergoes a global movement propagated from ligand-induced local conformational changes upon activation. In this study, we identified a functionally critical residue, Tyr404, at the C-terminus of the S4 helix, whose mutations to tryptophan and alanine yield gain- and loss-of-function channels, respectively.

Structural mechanism of allosteric activation of TRPML1 by PI(3,5)P and rapamycin.

Transient receptor potential mucolipin 1 (TRPML1) is a Ca-permeable, nonselective cation channel ubiquitously expressed in the endolysosomes of mammalian cells and its loss-of-function mutations are the direct cause of type IV mucolipidosis (MLIV), an autosomal recessive lysosomal storage disease. TRPML1 is a ligand-gated channel that can be activated by phosphatidylinositol 3,5-bisphosphate [PI(3,5)P] as well as some synthetic small-molecule agonists. Recently, rapamycin has also been shown to directly bind and activate TRPML1.

Voltage-gating and cytosolic Ca activation mechanisms of two-pore channel AtTPC1.

two-pore channel AtTPC1 is a voltage-gated, Ca-modulated, nonselective cation channel that is localized in the vacuolar membrane and responsible for generating slow vacuolar (SV) current. Under depolarizing membrane potential, cytosolic Ca activates AtTPC1 by binding at the EF-hand domain, whereas luminal Ca inhibits the channel by stabilizing the voltage-sensing domain II (VSDII) in the resting state. Here, we present 2.

Molecular Basis of Ubiquitination Catalyzed by the Bacterial Transglutaminase MavC.

The effector MavC is a transglutaminase that carries out atypical ubiquitination of the host ubiquitin (Ub)-conjugation enzyme UBE2N by catalyzing the formation of an isopeptide bond between Gln40 and Lys92, which leads to inhibition of signaling in the NF-κB pathway. In the absence of UBE2N, MavC deamidates Ub at Gln40 or catalyzes self-ubiquitination. However, the mechanisms underlying these enzymatic activities of MavC are poorly understood at the molecular level.

The bacterial deubiquitinase Ceg23 regulates the association of Lys-63-linked polyubiquitin molecules on the phagosome.

is the causative agent of the lung malady Legionnaires' disease, it modulates host function to create a niche termed the -containing vacuole (LCV) that permits intracellular replication. One important aspect of such modulation is the co-option of the host ubiquitin network with a panel of effector proteins. Here, using recombinantly expressed and purified proteins, analytic ultracentrifugation, structural analysis, and computational modeling, along with deubiquitinase (DUB), and bacterial infection assays, we found that the bacterial defective in organelle trafficking/intracellular multiplication effector Ceg23 is a member of the ovarian tumor (OTU) DUB family.

Legionella pneumophila regulates the activity of UBE2N by deamidase-mediated deubiquitination.

The Legionella pneumophila effector MavC induces ubiquitination of the E2 ubiquitin-conjugating enzyme UBE2N by transglutamination, thereby abolishing its function in the synthesis of K -type polyubiquitin chains. The inhibition of UBE2N activity creates a conundrum because this E2 enzyme is important in multiple signaling pathways, including some that are important for intracellular L. pneumophila replication.

Regulation of phosphoribosyl ubiquitination by a calmodulin-dependent glutamylase.

The bacterial pathogen Legionella pneumophila creates an intracellular niche permissive for its replication by extensively modulating host-cell functions using hundreds of effector proteins delivered by its Dot/Icm secretion system. Among these, members of the SidE family (SidEs) regulate several cellular processes through a unique phosphoribosyl ubiquitination mechanism that bypasses the canonical ubiquitination machinery. The activity of SidEs is regulated by another Dot/Icm effector known as SidJ; however, the mechanism of this regulation is not completely understood.

Legionella pneumophila inhibits immune signalling via MavC-mediated transglutaminase-induced ubiquitination of UBE2N.

The bacterial pathogen Legionella pneumophila modulates host immunity using effectors translocated by its Dot/Icm transporter to facilitate its intracellular replication. A number of these effectors employ diverse mechanisms to interfere with protein ubiquitination, a post-translational modification essential for immunity. Here, we have found that L.

Insights into catalysis and function of phosphoribosyl-linked serine ubiquitination.

Conventional ubiquitination regulates key cellular processes by catalysing the ATP-dependent formation of an isopeptide bond between ubiquitin (Ub) and primary amines in substrate proteins . Recently, the SidE family of bacterial effector proteins (SdeA, SdeB, SdeC and SidE) from pathogenic Legionella pneumophila were shown to use NAD to mediate phosphoribosyl-linked ubiquitination of serine residues in host proteins. However, the molecular architecture of the catalytic platform that enables this complex multistep process remains unknown.

Mechanism of inhibition of retromer transport by the bacterial effector RidL.

Retrograde vesicle trafficking pathways are responsible for returning membrane-associated components from endosomes to the Golgi apparatus and the endoplasmic reticulum (ER), and they are critical for maintaining organelle identity, lipid homeostasis, and many other cellular functions. The retrograde transport pathway has emerged as an important target for intravacuolar bacterial pathogens. The opportunistic pathogen exploits both the secretory and recycling branches of the vesicle transport pathway for intracellular bacterial proliferation.