Coronins are involved in the regulation of actin dynamics in a multifaceted way, participating in cell migration and vesicular trafficking. Apicomplexan parasites, which exhibit an actin‐dependent gliding motility that is essential for traversal through tissues, as well as invasion of and egress from host cells, express only a single coronin, whereas higher eukaryotes possess several isoforms. We set out to characterize the 3‐D structure, biochemical function, subcellular localization, and genetic ablation of Toxoplasma gondii coronin (TgCOR), to shed light on its biological role. A combination of X‐ray crystallography, small‐angle scattering of X‐rays, and light scattering revealed the atomic structure of the conserved WD40 domain and the dimeric arrangement of the full‐length protein. TgCOR binds to F‐actin and increases the rate and extent of actin polymerization. In vivo , TgCOR relocalizes transiently to the posterior pole of motile and invading parasites, independent of actin dynamics, but concomitant to microneme secretory organelle discharge. TgCOR contributes to, but is not essential for, invasion and egress. Taken together, our data point toward a role for TgCOR in stabilizing newly formed, short filaments and F‐actin cross‐linking, as well as functions linked to endocytosis and recycling of membranes.—Salamun, J., Kallio, J. P., Daher, W., Soldati‐Favre, D., Kursula, I., Structure of Toxoplasma gondii coronin, an actin‐binding protein that relocalizes to the posterior pole of invasive parasites and contributes to invasion and egress. FASEB J. 28, 4729–4747 (2014). www.fasebj.org

Laccases are copper‐containing enzymes used in various applications, such as textile bleaching. Several crystal structures of laccases from fungi and bacteria are available, but ascomycete types of fungal laccases (asco‐laccases) have been rather unexplored, and to date only the crystal structure of Melanocarpus albomyces laccase (MaL) has been published. We have now solved the crystal structure of another asco‐laccase, from Thielavia arenaria (TaLcc1), at 2.5 Å resolution. The loops near the T1 copper, forming the substrate‐binding pockets of the two asco‐laccases, differ to some extent, and include the amino acid thought to be responsible for catalytic proton transfer, which is Asp in TaLcc1, and Glu in MaL. In addition, the crystal structure of TaLcc1 does not have a chloride attached to the T2 copper, as observed in the crystal structure of MaL. The unique feature of TaLcc1 and MaL as compared with other laccases structures is that, in both structures, the processed C‐terminus blocks the T3 solvent channel leading towards the trinuclear centre, suggesting a common functional role for this conserved ‘C‐terminal plug’. We propose that the asco‐laccases utilize the C‐terminal carboxylic group in proton transfer processes, as has been suggested for Glu498 in the CotA laccase from Bacillus subtilis. The crystal structure of TaLcc1 also shows the formation of a similar weak homodimer, as observed for MaL, that may determine the properties of these asco‐laccases at high protein concentrations.Database Structural data are available in the Protein Data Bank database under the accession numbers 3PPS and 2VDZStructured digital abstract laccase binds to laccase by x‐ray crystallography (View interaction)

Acute intermittent porphyria (AIP) is an autosomal dominant inherited disease with low clinical penetrance, caused by mutations in the hydroxymethylbilane synthase (HMBS) gene, which encodes the third enzyme in the haem biosynthesis pathway. In susceptible HMBS mutation carriers, triggering factors such as hormonal changes and commonly used drugs induce an overproduction and accumulation of toxic haem precursors in the liver. Clinically, this presents as acute attacks characterised by severe abdominal pain and a wide array of neurological and psychiatric symptoms, and, in the long-term setting, the development of primary liver cancer, hypertension and kidney failure. Treatment options are few, and therapies preventing the development of symptomatic disease and long-term complications are non-existent. Here, we provide an overview of the disorder and treatments already in use in clinical practice, in addition to other therapies under development or in the pipeline. We also introduce the pathomechanistic effects of HMBS mutations, and present and discuss emerging therapeutic options based on HMBS stabilisation and the regulation of proteostasis. These are novel mechanistic therapeutic approaches with the potential of prophylactic correction of the disease by totally or partially recovering the enzyme functionality. The present scenario appears promising for upcoming patient-tailored interventions in AIP.

Rhoptries are club-shaped, regulated secretory organelles that cluster at the apical pole of apicomplexan parasites. Their discharge is essential for invasion and the establishment of an intracellular lifestyle. Little is known about rhoptry biogenesis and recycling during parasite division. In Toxoplasma gondii, positioning of rhoptries involves the armadillo repeats only protein (ARO) and myosin F (MyoF). Here, we show that two ARO partners, ARO-interacting protein (AIP) and adenylate cyclase β (ACβ) localize to a rhoptry subcompartment. In absence of AIP, ACβ disappears from the rhoptries. By assessing the contribution of each ARO armadillo (ARM) repeat, we provide evidence that ARO is multifunctional, participating not only in positioning but also in clustering of rhoptries. Structural analyses show that ARO resembles the myosin-binding domain of the Caenorhabditis elegans myosin chaperone UNC-45. A conserved patch of aromatic and acidic residues denotes the putative MyoF-binding site, and the overall arrangement of the ARM repeats explains the dramatic consequences of deleting each of them. Finally, Plasmodium falciparum ARO functionally complements ARO depletion and interacts with the same partners, highlighting the conservation of rhoptry biogenesis in Apicomplexa.