No abstract

P-type ATPases are ubiquitous primary transporters that pump cations across cell membranes through the formation and breakdown of a phosphoenzyme intermediate. Structural investigations suggest a transport mechanism defined by conformational changes in the cytoplasmic domains of the protein that are allosterically coupled to transmembrane helices so as to expose ion binding sites to alternate sides of the membrane. Here, we have employed single-molecule fluorescence resonance energy transfer (smFRET) to directly observe conformational changes associated with the functional transitions in the Listeria monocytogenes Ca2+-ATPase (LMCA1), an orthologue of eukaryotic Ca2+-ATPases. Using the smFRET approach we identify key intermediates with no known crystal structures, and our findings delineate reversible and an essentially irreversible step in the transport process wherein Ca2+ efflux by LMCA1 is rate limited by phosphoenzyme formation and resolved by ADP and Ca2+ release leading to an open E2P state.

We have characterized a putative Ca 2؉ -ATPase from the pathogenic bacterium Listeria monocytogenes with the locus tag lmo0841.

No abstract

Dimethyl fumarate (DMF) has been applied for decades in the treatment of psoriasis and now also multiple sclerosis. However, the mechanism of action has remained obscure and involves high dose over long time of this small, reactive compound implicating many potential targets. Based on a 1.9 Å resolution crystal structure of the C-terminal kinase domain of the mouse p90 Ribosomal S6 Kinase 2 (RSK2) inhibited by DMF we describe a central binding site in RSKs and the closely related Mitogen and Stress-activated Kinases (MSKs). DMF reacts covalently as a Michael acceptor to a conserved cysteine residue in the αF-helix of RSK/MSKs. Binding of DMF prevents the activation loop of the kinase from engaging substrate, and stabilizes an auto-inhibitory αL-helix, thus pointing to an effective, allosteric mechanism of kinase inhibition. The biochemical and cell biological characteristics of DMF inhibition of RSK/MSKs are consistent with the clinical protocols of DMF treatment.

The identification of the first small-molecule ligand of the neuronal receptor sortilin and structure determination of the receptor–ligand complex are reported.

Sortilin is a neuronal receptor involved in transmembrane signaling, endocytosis, and intracellular sorting of proteins. It cycles through a number of cellular compartments where it encounters various acidic conditions. The crystal structure of the sortilin ectodomain has previously been determined at neutral pH. Here, we present the 3.5-Å resolution crystal structure of sortilin at pH 5.5, which represents an environment similar to that of late endosomes, where ligands are released. The structure reveals an overall distortion of the 10-bladed β-propeller domain. This distortion and specific conformational changes, caused by protonation of a number of histidine residues, render the currently known binding sites unavailable for ligand binding. Access to the binding sites is furthermore blocked by a reversible and pH-dependent formation of tight sortilin dimers, also confirmed by electron microscopy, size-exclusion chromatography, and mutational studies. This study reveals how sortilin binding sites are disrupted and explains pH-dependent ligand affinity.

The sarcoplasmic/endoplasmic reticulum Ca2+‐ATPase 2a (SERCA2a) performs active reuptake of cytoplasmic Ca2+ and is a major regulator of cardiac muscle contractility. Dysfunction or dysregulation of SERCA2a is associated with heart failure, while restoring its function is considered as a therapeutic strategy to restore cardiac performance. However, its structure has not yet been determined. Based on native, active protein purified from pig ventricular muscle, we present the first crystal structures of SERCA2a, determined in the CPA‐stabilized E2−AlF4− form (3.3 Å) and the Ca2+‐occluded [Ca2]E1‐AMPPCP form (4.0 Å). The structures are similar to the skeletal muscle isoform SERCA1a pointing to a conserved mechanism. We seek to explain the kinetic differences between SERCA1a and SERCA2a. We find that several isoform‐specific residues are acceptor sites for post‐translational modifications. In addition, molecular dynamics simulations predict that isoform‐specific residues support distinct intramolecular interactions in SERCA2a and SERCA1a. Our experimental observations further indicate that isoform‐specific intramolecular interactions are functionally relevant, and may explain the kinetic differences between SERCA2a and SERCA1a.