Both chloride-binding sites are required for KCC2-mediated transport.

The K+-Cl- cotransporter 2 (KCC2) plays an important role in inhibitory neurotransmission, and its impairment is associated with neurological and psychiatric disorders, including epilepsy, schizophrenia, and autism. Although KCCs transport K+ and Cl- in a 1:1 stoichiometry, two Cl- coordination sites were indicated via cryo-EM. In a comprehensive analysis, we analyzed the consequences of point mutations of residues coordinating Cl- in Cl1 and Cl2. Individual mutations of residues in Cl1 and Cl2 reduce or abolish KCC2WT function, indicating a crucial role of both Cl- coordination sites for KCC2 function. Structural changes in the extracellular loop 2 by inserting a 3xHA tag switches the K+ coordination site to another position. To investigate, whether the extension of the extracellular loop 2 with the 3xHA tag also affects the coordination of the two Cl- coordination sites, we carried out the analogous experiments for both Cl- coordinating sites in the KCC2HA construct. These analyses showed that most of the individual mutation of residues in Cl1 and Cl2 in the KCC2HA construct reduces or abolishes KCC2 function, indicating that the coordination of Cl- remains at the same position. However, the coupling of K+ and Cl- in Cl1 is still apparent in the KCC2HA construct, indicating a mutual dependence of both ions. In addition, the coordination residue Tyr569 in Cl2 shifted in KCC2HA. Thus, conformational changes in the extracellular domain affect K+ and Cl--binding sites. However, the effect on the Cl--binding sites is subtler.

Linking the Autotaxin-LPA Axis to Medicinal Cannabis and the Endocannabinoid System.

Over the past few decades, many current uses for cannabinoids have been described, ranging from controlling epilepsy to neuropathic pain and anxiety treatment. Medicines containing cannabinoids have been approved by both the FDA and the EMA for the control of specific diseases for which there are few alternatives. However, the molecular-level mechanism of action of cannabinoids is still poorly understood. Recently, cannabinoids have been shown to interact with autotaxin (ATX), a secreted lysophospholipase D enzyme responsible for catalyzing lysophosphatidylcholine (LPC) to lysophosphatidic acid (LPA), a pleiotropic growth factor that interacts with LPA receptors. In addition, a high-resolution structure of ATX in complex with THC has recently been published, accompanied by biochemical studies investigating this interaction. Due to their LPA-like structure, endocannabinoids have been shown to interact with ATX in a less potent manner. This finding opens new areas of research regarding cannabinoids and endocannabinoids, as it could establish the effect of these compounds at the molecular level, particularly in relation to inflammation, which cannot be explained by the interaction with CB1 and CB2 receptors alone. Further research is needed to elucidate the mechanism behind the interaction between cannabinoids and endocannabinoids in humans and to fully explore the therapeutic potential of such approaches.

PRG3 and PRG5 C-Termini: Important Players in Early Neuronal Differentiation.

The functional importance of neuronal differentiation of the transmembrane proteins' plasticity-related genes 3 (PRG3) and 5 (PRG5) has been shown. Although their sequence is closely related, they promote different morphological changes in neurons. PRG3 was shown to promote neuritogenesis in primary neurons; PRG5 contributes to spine induction in immature neurons and the regulation of spine density and morphology in mature neurons. Both exhibit intracellularly located C-termini of less than 50 amino acids. Varying C-termini suggested that these domains shape neuronal morphology differently. We generated mutant EGFP-fusion proteins in which the C-termini were either swapped between PRG3 and PRG5, deleted, or fused to another family member, plasticity-related gene 4 (PRG4), that was recently shown to be expressed in different brain regions. We subsequently analyzed the influence of overexpression in immature neurons. Our results point to a critical role of the PRG3 and PRG5 C-termini in shaping early neuronal morphology. However, the results suggest that the C-terminus alone might not be sufficient for promoting the morphological effects induced by PRG3 and PRG5.

Structural snapshots of the catalytic cycle of the phosphodiesterase Autotaxin.

Autotaxin (ATX) is a secreted phosphodiesterase that produces the signalling lipid lysophosphatidic acid (LPA). The bimetallic active site of ATX is structurally related to the alkaline phosphatase superfamily. Here, we present a new crystal structure of ATX in complex with orthovanadate (ATX-VO5), which binds the Oγ nucleophile of Thr209 and adopts a trigonal bipyramidal conformation, following the nucleophile attack onto the substrate. We have now a portfolio of ATX structures we discuss as intermediates of the catalytic mechanism: the new ATX-VO5 structure; a unique structure where the nucleophile Thr209 is phosphorylated (ATX-pThr). Comparing these to a complex with the LPA product (ATX-LPA) and with a complex with a phosphate ion (ATX-PO4), that represent the Michaelis complex of the reaction, we observe movements of Thr209, changes in the relative displacement of the zinc ions, and a water molecule that likely fulfils the second nucleophilic attack. We propose that ATX follows the associative two-step in-line displacement mechanism.

The polybasic insertion in autotaxin α confers specific binding to heparin and cell surface heparan sulfate proteoglycans.

Autotaxin (ATX) is a secreted lysophospholipase D that generates the lipid mediator lysophosphatidic acid (LPA), playing a key role in diverse physiological and pathological processes. ATX exists in distinct splice variants, but isoform-specific functions remain elusive. Here we characterize the ATXα isoform, which differs from the canonical form (ATXß) in having a 52-residue polybasic insertion of unknown function in the catalytic domain. We find that the ATXα insertion is susceptible to cleavage by extracellular furin-like endoproteases, but cleaved ATXα remains structurally and functionally intact due to strong interactions within the catalytic domain. Through ELISA and surface plasmon resonance assays, we show that ATXα binds specifically to heparin with high affinity (K(d) ~10(-8) M), whereas ATXß does not; furthermore, heparin moderately enhanced the lysophospholipase D activity of ATXα. We further show that ATXα, but not ATXß, binds abundantly to SKOV3 carcinoma cells. ATXα binding was abolished after treating the cells with heparinase III, but not after chondroitinase treatment. Thus, the ATXα insertion constitutes a cleavable heparin-binding domain that mediates interaction with heparan sulfate proteoglycans, thereby targeting LPA production to the plasma membrane.

N-terminal domain of human Hsp90 triggers binding to the cochaperone p23.

The molecular chaperone Hsp90 is a protein folding machine that is conserved from bacteria to man. Human, cytosolic Hsp90 is dedicated to folding of chiefly signal transduction components. The chaperoning mechanism of Hsp90 is controlled by ATP and various cochaperones, but is poorly understood and controversial. Here, we characterized the Apo and ATP states of the 170-kDa human Hsp90 full-length protein by NMR spectroscopy in solution, and we elucidated the mechanism of the inhibition of its ATPase by its cochaperone p23. We assigned isoleucine side chains of Hsp90 via specific isotope labeling of their δ-methyl groups, which allowed the NMR analysis of the full-length protein. We found that ATP caused exclusively local changes in Hsp90's N-terminal nucleotide-binding domain. Native mass spectrometry showed that Hsp90 and p23 form a 22 complex via a positively cooperative mechanism. Despite this stoichiometry, NMR data indicated that the complex was not fully symmetric. The p23-dependent NMR shifts mapped to both the lid and the adenine end of Hsp90's ATP binding pocket, but also to large parts of the middle domain. Shifts distant from the p23 binding site reflect p23-induced conformational changes in Hsp90. Together, we conclude that it is Hsp90's nucleotide-binding domain that triggers the formation of the Hsp90(2)p23(2) complex. We anticipate that our NMR approach has significant impact on future studies of full-length Hsp90 with cofactors and substrates, but also for the development of Hsp90 inhibiting anticancer drugs.

Spotlight on plasticity-related genes: Current insights in health and disease.

The development of the central nervous system is highly complex, involving numerous developmental processes that must take place with high spatial and temporal precision. This requires a series of complex and well-coordinated molecular processes that are tighly controlled and regulated by, for example, a variety of proteins and lipids. Deregulations in these processes, including genetic mutations, can lead to the most severe maldevelopments. The present review provides an overview of the protein family Plasticity-related genes (PRG1-5), including their role during neuronal differentiation, their molecular interactions, and their participation in various diseases. As these proteins can modulate the function of bioactive lipids, they are able to influence various cellular processes. Furthermore, they are dynamically regulated during development, thus playing an important role in the development and function of synapses. First studies, conducted not only in mouse experiments but also in humans, revealed that mutations or dysregulations of these proteins lead to changes in lipid metabolism, resulting in severe neurological deficits. In recent years, as more and more studies have shown their involvement in a broad range of diseases, the complexity and broad spectrum of known and as yet unknown interactions between PRGs, lipids, and proteins make them a promising and interesting group of potential novel therapeutic targets.

Linking medicinal cannabis to autotaxin-lysophosphatidic acid signaling.

Autotaxin is primarily known for the formation of lysophosphatidic acid (LPA) from lysophosphatidylcholine. LPA is an important signaling phospholipid that can bind to six G protein-coupled receptors (LPA1-6). The ATX-LPA signaling axis is a critical component in many physiological and pathophysiological conditions. Here, we describe a potent inhibition of Δ9-trans-tetrahydrocannabinol (THC), the main psychoactive compound of medicinal cannabis and related cannabinoids, on the catalysis of two isoforms of ATX with nanomolar apparent EC50 values. Furthermore, we decipher the binding interface of ATX to THC, and its derivative 9(R)-Δ6a,10a-THC (6a10aTHC), by X-ray crystallography. Cellular experiments confirm this inhibitory effect, revealing a significant reduction of internalized LPA1 in the presence of THC with simultaneous ATX and lysophosphatidylcholine stimulation. Our results establish a functional interaction of THC with autotaxin-LPA signaling and highlight novel aspects of medicinal cannabis therapy.

Unfolding of metastable linker region is at the core of Hsp33 activation as a redox-regulated chaperone.

Hsp33, a molecular chaperone specifically activated by oxidative stress conditions that lead to protein unfolding, protects cells against oxidative protein aggregation. Stress sensing in Hsp33 occurs via its C-terminal redox switch domain, which consists of a zinc center that responds to the presence of oxidants and an adjacent metastable linker region, which responds to unfolding conditions. Here we show that single mutations in the N terminus of Hsp33 are sufficient to either partially (Hsp33-M172S) or completely (Hsp33-Y12E) abolish this post-translational regulation of Hsp33 chaperone function. Both mutations appear to work predominantly via the destabilization of the Hsp33 linker region without affecting zinc coordination, redox sensitivity, or substrate binding of Hsp33. We found that the M172S substitution causes moderate destabilization of the Hsp33 linker region, which seems sufficient to convert the redox-regulated Hsp33 into a temperature-controlled chaperone. The Y12E mutation leads to the constitutive unfolding of the Hsp33 linker region thereby turning Hsp33 into a constitutively active chaperone. These results demonstrate that the redox-controlled unfolding of the Hsp33 linker region plays the central role in the activation process of Hsp33. The zinc center of Hsp33 appears to act as the redox-sensitive toggle that adjusts the thermostability of the linker region to the cell redox status. In vivo studies confirmed that even mild overexpression of the Hsp33-Y12E mutant protein inhibits bacterial growth, providing important evidence that the tight functional regulation of Hsp33 chaperone activity plays a vital role in bacterial survival.

Target highlights in CASP9: Experimental target structures for the critical assessment of techniques for protein structure prediction.

One goal of the CASP community wide experiment on the critical assessment of techniques for protein structure prediction is to identify the current state of the art in protein structure prediction and modeling. A fundamental principle of CASP is blind prediction on a set of relevant protein targets, that is, the participating computational methods are tested on a common set of experimental target proteins, for which the experimental structures are not known at the time of modeling. Therefore, the CASP experiment would not have been possible without broad support of the experimental protein structural biology community. In this article, several experimental groups discuss the structures of the proteins which they provided as prediction targets for CASP9, highlighting structural and functional peculiarities of these structures: the long tail fiber protein gp37 from bacteriophage T4, the cyclic GMP-dependent protein kinase Iß dimerization/docking domain, the ectodomain of the JTB (jumping translocation breakpoint) transmembrane receptor, Autotaxin in complex with an inhibitor, the DNA-binding J-binding protein 1 domain essential for biosynthesis and maintenance of DNA base-J (ß-D-glucosyl-hydroxymethyluracil) in Trypanosoma and Leishmania, an so far uncharacterized 73 residue domain from Ruminococcus gnavus with a fold typical for PDZ-like domains, a domain from the phycobilisome core-membrane linker phycobiliprotein ApcE from Synechocystis, the heat shock protein 90 activators PFC0360w and PFC0270w from Plasmodium falciparum, and 2-oxo-3-deoxygalactonate kinase from Klebsiella pneumoniae.

Obstacles and Solutions Driving the Development of a National Teleradiology Network.

BACKGROUND: Teleradiology has the potential to link medical experts and specialties despite geographical separation. In a project report about hospital-based teleradiology, the significance of technical and human factors during the implementation and growth of a teleradiology network are explored. EVALUATION: The article identifies major obstacles during the implementation and growth of the teleradiology network of the Berlin Trauma Hospital (BG Unfallkrankenhaus Berlin) between 2004 and 2020 in semi-structured interviews with senior staff members. Quantitative analysis of examination numbers, patient numbers, and profits relates the efforts of the staff members to the monetary benefits and success of the network. Identification of qualitative and quantitative factors for success: Soft and hard facilitators and solutions driving the development of the national teleradiology network are identified. Obstacles were often solved by technical innovations, but the time span between required personal efforts, endurance, and flexibility of local and external team members. The article describes innovations driven by teleradiology and hints at the impact of teleradiology on modern medical care by relating the expansion of the teleradiology network to patient transfers and profits. CONCLUSION: In addition to technical improvements, interpersonal collaborations were key to the success of the teleradiology network of the Berlin Trauma Hospital and remained a unique feature and selling point of this teleradiology network.

Crystallization and preliminary X-ray diffraction analysis of rat autotaxin.

Rat autotaxin has been cloned, expressed, purified to homogeneity and crystallized via hanging-drop vapour diffusion using PEG 3350 as precipitant and ammonium iodide and sodium thiocyanate as salts. The crystals diffracted to a maximum resolution of 2.05 A and belonged to space group P1, with unit-cell parameters a=53.8, b=63.3, c=70.5 A, alpha=98.8, beta=106.2, gamma=99.8 degrees. Preliminary X-ray diffraction analysis indicated the presence of one molecule per asymmetric unit, with a solvent content of 47%.

Mammalian cell expression, purification, crystallization and microcrystal data collection of autotaxin/ENPP2, a secreted mammalian glycoprotein.

Autotaxin (ATX or ENPP2) is a secreted glycosylated mammalian enzyme that exhibits lysophospholipase D activity, hydrolyzing lysophosphatidylcholine to the signalling lipid lysophosphatidic acid. ATX is an approximately 100 kDa multi-domain protein encompassing two N-terminal somatomedin B-like domains, a central catalytic phosphodiesterase domain and a C-terminal nuclease-like domain. Protocols for the efficient expression of ATX from stably transfected mammalian HEK293 cells in amounts sufficient for crystallographic studies are reported. Purification resulted in protein that crystallized readily, but various attempts to grow crystals suitable in size for routine crystallographic structure determination were not successful. However, the available micrometre-thick plates diffracted X-rays beyond 2.0 A resolution and allowed the collection of complete diffraction data to about 2.6 A resolution. The problems encountered and the current advantages and limitations of diffraction data collection from thin crystal plates are discussed.

Steroid binding to Autotaxin links bile salts and lysophosphatidic acid signalling.

Autotaxin (ATX) generates the lipid mediator lysophosphatidic acid (LPA). ATX-LPA signalling is involved in multiple biological and pathophysiological processes, including vasculogenesis, fibrosis, cholestatic pruritus and tumour progression. ATX has a tripartite active site, combining a hydrophilic groove, a hydrophobic lipid-binding pocket and a tunnel of unclear function. We present crystal structures of rat ATX bound to 7α-hydroxycholesterol and the bile salt tauroursodeoxycholate (TUDCA), showing how the tunnel selectively binds steroids. A structure of ATX simultaneously harbouring TUDCA in the tunnel and LPA in the pocket, together with kinetic analysis, reveals that bile salts act as partial non-competitive inhibitors of ATX, thereby attenuating LPA receptor activation. This unexpected interplay between ATX-LPA signalling and select steroids, notably natural bile salts, provides a molecular basis for the emerging association of ATX with disorders associated with increased circulating levels of bile salts. Furthermore, our findings suggest potential clinical implications in the use of steroid drugs.

Structure-function relationships of autotaxin, a secreted lysophospholipase D.

Autotaxin (ATX or ENPP2) is an ectonucleotide pyrophosphatase/phosphodiesterase (ENPP) that functions as a secreted lysophospholipase D to produce the multifunctional lipid mediator lysophosphatidic acid (LPA) from more complex lysophospholipids. LPA acts on distinct G protein-coupled receptors thereby activating multiple signaling cascades and cellular responses. The ATX-LPA signaling axis is implicated in a remarkably wide variety of physiological and pathological processes, ranging from vascular and neural development to lymphocyte homing, fibrosis and cancer. Despite much progress in understanding LPA receptor signaling, the precise mode of action of ATX has long remained elusive due to the lack of structural data. In particular, it has been unclear what makes ATX a unique lysophospholipase D and how the enzyme is targeted to LPA-responsive cells. Recent structural studies have begun to clarify these issues. Here we discuss new insights and inferences from the ATX structure.

Structure-based design of novel boronic acid-based inhibitors of autotaxin.

Autotaxin (ATX) is a secreted phosphodiesterase that hydrolyzes the abundant phospholipid lysophosphatidylcholine (LPC) to produce lysophosphatidic acid (LPA). The ATX-LPA signaling axis has been implicated in inflammation, fibrosis, and tumor progression, rendering ATX an attractive drug target. We recently described a boronic acid-based inhibitor of ATX, named HA155 (1). Here, we report the design of new inhibitors based on the crystal structure of ATX in complex with inhibitor 1. Furthermore, we describe the syntheses and activities of these new inhibitors, whose potencies can be explained by structural data. To understand the difference in activity between two different isomers with nanomolar potencies, we performed molecular docking experiments. Intriguingly, molecular docking suggested a remarkable binding pose for one of the isomers, which differs from the original binding pose of inhibitor 1 for ATX, opening further options for inhibitor design.

Structural basis of substrate discrimination and integrin binding by autotaxin.

Autotaxin (ATX, also known as ectonucleotide pyrophosphatase/phosphodiesterase-2, ENPP2) is a secreted lysophospholipase D that generates the lipid mediator lysophosphatidic acid (LPA), a mitogen and chemoattractant for many cell types. ATX-LPA signaling is involved in various pathologies including tumor progression and inflammation. However, the molecular basis of substrate recognition and catalysis by ATX and the mechanism by which it interacts with target cells are unclear. Here, we present the crystal structure of ATX, alone and in complex with a small-molecule inhibitor. We have identified a hydrophobic lipid-binding pocket and mapped key residues for catalysis and selection between nucleotide and phospholipid substrates. We have shown that ATX interacts with cell-surface integrins through its N-terminal somatomedin B-like domains, using an atypical mechanism. Our results define determinants of substrate discrimination by the ENPP family, suggest how ATX promotes localized LPA signaling and suggest new approaches for targeting ATX with small-molecule therapeutic agents.