Substrate recognition and allosteric regulation of synaptic vesicle glutamate transporter VGLUT2.

The concentration of neurotransmitters inside synaptic vesicles (SVs) underlies the quantal nature of synaptic transmission. Uptake of glutamate, the principal excitatory neurotransmitter, is driven by membrane potential. To prevent nonquantal efflux of glutamate after SV exocytosis, the vesicular glutamate transporters (VGLUTs) are allosterically inhibited by the neutral pH of the synaptic cleft.

Structure and dynamics of the essential endogenous mycobacterial polyketide synthase Pks13.

The mycolic acid layer of the Mycobacterium tuberculosis cell wall is essential for viability and virulence, and the enzymes responsible for its synthesis are targets for antimycobacterial drug development. Polyketide synthase 13 (Pks13) is a module encoding several enzymatic and transport functions that carries out the condensation of two different long-chain fatty acids to produce mycolic acids. We determined structures by cryogenic-electron microscopy of dimeric multi-enzyme Pks13 purified from mycobacteria under normal growth conditions, captured with native substrates.

Structure and dynamics of the essential endogenous mycobacterial polyketide synthase Pks13.

is currently the leading cause of death by any bacterial infection. The mycolic acid layer of the cell wall is essential for viability and virulence, and the enzymes responsible for its synthesis are therefore front line targets for antimycobacterial drug development. Polyketide synthase 13 (Pks13) is a module comprised of a closely symmetric parallel dimer of chains, each encoding several enzymatic and transport functions, that carries out the condensation of two different very long chain fatty acids to produce mycolic acids that are essential components of the mycobacterial cell wall.

Diversity of function and mechanism in a family of organic anion transporters.

Originally identified as transporters for inorganic phosphate, solute carrier 17 (SLC17) family proteins subserve diverse physiological roles. The vesicular glutamate transporters (VGLUTs) package the principal excitatory neurotransmitter glutamate into synaptic vesicles (SVs). In contrast, the closely related sialic acid transporter sialin mediates the flux of sialic acid in the opposite direction, from lysosomes to the cytoplasm.

Caught in Action: X-ray Structure of Thymidylate Synthase with Noncovalent Intermediate Analog.

Methylation of 2-deoxyuridine-5'-monophosphate (dUMP) at the C5 position by the obligate dimeric thymidylate synthase (TSase) in the sole biosynthetic pathway to thymidine 5'-monophosphate (dTMP) proceeds by forming a covalent ternary complex with dUMP and cosubstrate 5,10-methylenetetrahydrofolate. The crystal structure of an analog of this intermediate gives important mechanistic insights but does not explain the half-of-the-sites activity of the enzyme. Recent experiments showed that the C5 proton and the catalytic Cys are eliminated in a concerted manner from the covalent ternary complex to produce a noncovalent bisubstrate intermediate.

Ion transport and regulation in a synaptic vesicle glutamate transporter.

Synaptic vesicles accumulate neurotransmitters, enabling the quantal release by exocytosis that underlies synaptic transmission. Specific neurotransmitter transporters are responsible for this activity and therefore are essential for brain function. The vesicular glutamate transporters (VGLUTs) concentrate the principal excitatory neurotransmitter glutamate into synaptic vesicles, driven by membrane potential.

Diversity in kinetics correlated with structure in nano body-stabilized LacY.

The structure of lactose permease, stabilized in a periplasmic open conformation by two Gly to Trp replacements (LacYww) and complexed with a nanobody directed against this conformation, provides the highest resolution structure of the symporter. The nanobody binds in a different manner than two other nanobodies made against the same mutant, which also bind to the same general region on the periplasmic side. This region of the protein may represent an immune hotspot.

Crystal Structure of a ligand-bound LacY-Nanobody Complex.

The lactose permease of (LacY), a dynamic polytopic membrane transport protein, catalyzes galactoside/H symport and operates by an alternating access mechanism that exhibits multiple conformations, the distribution of which is altered by sugar-binding. Camelid nanobodies were made against a double-mutant Gly46 → Trp/Gly262 → Trp (LacY) that produces an outward-open conformation, as opposed to the cytoplasmic open-state crystal structure of WT LacY. Nanobody 9047 (Nb9047) stabilizes WT LacY in a periplasmic-open conformation.

A Single Mutation Traps a Half-Sites Reactive Enzyme in Midstream, Explaining Asymmetry in Hydride Transfer.

In Escherichia coli thymidylate synthase (EcTS), rate-determining hydride transfer from the cofactor 5,10-methylene-5,6,7,8-tetrahydrofolate to the intermediate 5-methylene-2'-deoxyuridine 5'-monophosphate occurs by hydrogen tunneling, requiring precise alignment of reactants and a closed binding cavity, sealed by the C-terminal carboxyl group. Mutations that destabilize the closed conformation of the binding cavity allow small molecules such as β-mercaptoethanol (β-ME) to enter the active site and compete with hydride for addition to the 5-methylene group of the intermediate. The C-terminal deletion mutant of EcTS produced the β-ME adduct in proportions that varied dramatically with cofactor concentration, from 50% at low cofactor concentrations to 0% at saturating cofactor conditions, suggesting communication between active sites.

Mechanism of inhibition of human glucose transporter GLUT1 is conserved between cytochalasin B and phenylalanine amides.

Cancerous cells have an acutely increased demand for energy, leading to increased levels of human glucose transporter 1 (hGLUT1). This up-regulation suggests hGLUT1 as a target for therapeutic inhibitors addressing a multitude of cancer types. Here, we present three inhibitor-bound, inward-open structures of WT-hGLUT1 crystallized with three different inhibitors: cytochalasin B, a nine-membered bicyclic ring fused to a 14-membered macrocycle, which has been described extensively in the literature of hGLUTs, and two previously undescribed Phe amide-derived inhibitors.

Crystal Structure of the Human tRNA m(1)A58 Methyltransferase-tRNA(3)(Lys) Complex: Refolding of Substrate tRNA Allows Access to the Methylation Target.

Human tRNA3(Lys) is the primer for reverse transcription of HIV; the 3' end is complementary to the primer-binding site on HIV RNA. The complementarity ends at the 18th base, A58, which in tRNA3(Lys) is modified to remove Watson-Crick pairing. Motivated to test the role of the modification in terminating the primer-binding sequence and thus limiting run-on transcription, we asked how the modification of RNA could be accomplished.

Structure of LacY with an α-substituted galactoside: Connecting the binding site to the protonation site.

The X-ray crystal structure of a conformationally constrained mutant of the Escherichia coli lactose permease (the LacY double-Trp mutant Gly-46→Trp/Gly-262→Trp) with bound p-nitrophenyl-α-d-galactopyranoside (α-NPG), a high-affinity lactose analog, is described. With the exception of Glu-126 (helix IV), side chains Trp-151 (helix V), Glu-269 (helix VIII), Arg-144 (helix V), His-322 (helix X), and Asn-272 (helix VIII) interact directly with the galactopyranosyl ring of α-NPG to provide specificity, as indicated by biochemical studies and shown directly by X-ray crystallography. In contrast, Phe-20, Met-23, and Phe-27 (helix I) are within van der Waals distance of the benzyl moiety of the analog and thereby increase binding affinity nonspecifically.

Substrates Control Multimerization and Activation of the Multi-Domain ATPase Motor of Type VII Secretion.

Mycobacterium tuberculosis and Staphylococcus aureus secrete virulence factors via type VII protein secretion (T7S), a system that intriguingly requires all of its secretion substrates for activity. To gain insights into T7S function, we used structural approaches to guide studies of the putative translocase EccC, a unique enzyme with three ATPase domains, and its secretion substrate EsxB. The crystal structure of EccC revealed that the ATPase domains are joined by linker/pocket interactions that modulate its enzymatic activity.

Alanine mutants of the interface residues of human thymidylate synthase decode key features of the binding mode of allosteric anticancer peptides.

Allosteric peptide inhibitors of thymidylate synthase (hTS) bind to the dimer interface and stabilize the inactive form of the protein. Four interface residues were mutated to alanine, and interaction studies were employed to decode the key role of these residues in the peptide molecular recognition. This led to the identification of three crucial interface residues F59, L198, and Y202 that impart activity to the peptide inhibitors and suggest the binding area for further inhibitor design.

Structure of a new DNA-binding domain which regulates pathogenesis in a wide variety of fungi.

WOPR-domain proteins are found throughout the fungal kingdom where they function as master regulators of cell morphology and pathogenesis. Genetic and biochemical experiments previously demonstrated that these proteins bind to specific DNA sequences and thereby regulate transcription. However, their primary sequence showed no relationship to any known DNA-binding domain, and the basis for their ability to recognize DNA sequences remained unknown.

Architecture of a single membrane spanning cytochrome P450 suggests constraints that orient the catalytic domain relative to a bilayer.

Bitopic integral membrane proteins with a single transmembrane helix play diverse roles in catalysis, cell signaling, and morphogenesis. Complete monospanning protein structures are needed to show how interaction between the transmembrane helix and catalytic domain might influence association with the membrane and function. We report crystal structures of full-length Saccharomyces cerevisiae lanosterol 14α-demethylase, a membrane monospanning cytochrome P450 of the CYP51 family that catalyzes the first postcyclization step in ergosterol biosynthesis and is inhibited by triazole drugs.

Structure of sugar-bound LacY.

Here we describe the X-ray crystal structure of a double-Trp mutant (Gly46→Trp/Gly262→Trp) of the lactose permease of Escherichia coli (LacY) with a bound, high-affinity lactose analog. Although thought to be arrested in an open-outward conformation, the structure is almost occluded and is partially open to the periplasmic side; the cytoplasmic side is tightly sealed. Surprisingly, the opening on the periplasmic side is sufficiently narrow that sugar cannot get in or out of the binding site.

The mechanism of pseudouridine synthases from a covalent complex with RNA, and alternate specificity for U2605 versus U2604 between close homologs.

RluB catalyses the modification of U2605 to pseudouridine (Ψ) in a stem-loop at the peptidyl transferase center of Escherichia coli 23S rRNA. The homolog RluF is specific to the adjacent nucleotide in the stem, U2604. The 1.

Development and binding mode assessment of N-[4-[2-propyn-1-yl[(6S)-4,6,7,8-tetrahydro-2-(hydroxymethyl)-4-oxo-3H-cyclopenta[g]quinazolin-6-yl]amino]benzoyl]-l-γ-glutamyl-D-glutamic acid (BGC 945), a novel thymidylate synthase inhibitor that targets tumor cells.

N-[4-[2-Propyn-1-yl[(6S)-4,6,7,8-tetrahydro-2-(hydroxymethyl)-4-oxo-3H-cyclopenta[g]quinazolin-6-yl]amino]benzoyl]-l-γ-glutamyl-d-glutamic acid 1 (BGC 945, now known as ONX 0801), is a small molecule thymidylate synthase (TS) inhibitor discovered at the Institute of Cancer Research in London. It is licensed by Onyx Pharmaceuticals and is in phase 1 clinical studies. It is a novel antifolate drug resembling TS inhibitors plevitrexed and raltitrexed that combines enzymatic inhibition of thymidylate synthase with α-folate receptor-mediated targeting of tumor cells.

In human pseudouridine synthase 1 (hPus1), a C-terminal helical insert blocks tRNA from binding in the same orientation as in the Pus1 bacterial homologue TruA, consistent with their different target selectivities.

Human pseudouridine (Ψ) synthase Pus1 (hPus1) modifies specific uridine residues in several non-coding RNAs: tRNA, U2 spliceosomal RNA, and steroid receptor activator RNA. We report three structures of the catalytic core domain of hPus1 from two crystal forms, at 1.8Å resolution.

Mg2+ binds to the surface of thymidylate synthase and affects hydride transfer at the interior active site.

Thymidylate synthase (TSase) produces the sole intracellular de novo source of thymidine (i.e., the DNA base T) and thus is a common target for antibiotic and anticancer drugs.

Inhibitor of ovarian cancer cells growth by virtual screening: a new thiazole derivative targeting human thymidylate synthase.

Human thymidylate synthase (hTS) was targeted through a virtual screening approach. The most optimal inhibitor identified, 2-{4-hydroxy-2-[(2-hydroxybenzylidene)hydrazono]-2,5-dihydrothiazol-5-yl}-N-(3-trifluoromethylphenyl)acetamide (5), showed a mixed-type inhibition pattern, with a K(i) of 1.3 μM and activity against ovarian cancer cell lines with the same potency as cisplatin.

LpxI structures reveal how a lipid A precursor is synthesized.

Enzymes in lipid metabolism acquire and deliver hydrophobic substrates and products from within lipid bilayers. The structure at 2.55 Å of one isozyme of a constitutive enzyme in lipid A biosynthesis, LpxI from Caulobacter crescentus, has a novel fold.

A remote mutation affects the hydride transfer by disrupting concerted protein motions in thymidylate synthase.

The role of protein flexibility in enzyme-catalyzed activation of chemical bonds is an evolving perspective in enzymology. Here we examine the role of protein motions in the hydride transfer reaction catalyzed by thymidylate synthase (TSase). Being remote from the chemical reaction site, the Y209W mutation of Escherichia coli TSase significantly reduces the protein activity, despite the remarkable similarity between the crystal structures of the wild-type and mutant enzymes with ligands representing their Michaelis complexes.

EspR, a key regulator of Mycobacterium tuberculosis virulence, adopts a unique dimeric structure among helix-turn-helix proteins.

EspR is a transcriptional regulator that activates the ESX-1 secretion system during Mycobacterium tuberculosis infection and is critical for pathogenesis. It is unique among DNA-binding proteins as it is secreted as part of a feedback regulatory loop that serves to mitigate transcriptional activity. Here we report the crystal structure of a functional EspR dimer at 2.