Charles S. Bond

Structure of a human lysosomal sulfatase

BACKGROUNDn. Sulfatases catalyze the hydrolysis of sulfuric acid esters from a wide variety of substrates including glycosaminoglycans, glycolipids and steroids. There is sufficient common sequence similarity within the class of sulfatase enzymes to indicate that they have a common structure. Deficiencies of specific lysosomal sulfatases that are involved in the degradation of glycosamino-glycans lead to rare inherited clinical disorders termed mucopolysaccharidoses. In sufferers of multiple sulfatase deficiency, all sulfatases are inactive because an essential post-translational modification of a specific active-site cysteine residue to oxo-alanine does not occur. Studies of this disorder have contributed to location and characterization of the sulfatase active site. To understand the catalytic mechanism of sulfatases, and ultimately the determinants of their substrate specificities, we have determined the structure of N-acetylgalactosamine-4-sulfatase.nnnRESULTSn. The crystal structure of the enzyme has been solved and refined at 2.5 resolution using data recorded at both 123K and 273K. The structure has two domains, the larger of which belongs to the alpha/beta class of proteins and contains the active site. The enzyme active site in the crystals contains several hitherto undescribed features. The active-site cysteine residue, Cys91, is found as the sulfate derivative of the aldehyde species, oxo-alanine. The sulfate is bound to a previously undetected metal ion, which we have identified as calcium. The structure of a vanadate-inhibited form of the enzyme has also been solved, and this structure shows that vanadate has replaced sulfate in the active site and that the vanadate is covalently linked to the protein. Preliminary data is presented for crystals soaked in the monosaccharide N-acetylgalactosamine, the structure of which forms a product complex of the enzyme.nnnCONCLUSIONSn. The structure of N-acetylgalactosamine-4-sulfatase reveals that residues conserved amongst the sulfatase family are involved in stabilizing the calcium ion and the sulfate ester in the active site. This suggests an archetypal fold for the family of sulfatases. A catalytic role is proposed for the post-translationally modified highly conserved cysteine residue. Despite a lack of any previously detectable sequence similarity to any protein of known structure, the large sulfatase domain that contains the active site closely resembles that of alkaline phosphatase: the calcium ion in sulfatase superposes on one of the zinc ions in alkaline phosphatase and the sulfate ester of Cys91 superposes on the phosphate ion found in the active site of alkaline phosphatase.

TopDraw: a sketchpad for protein structure topology cartoons

SUMMARYnProtein topology cartoons are a representation of structural data commonly used by structural biologists to illustrate the relationship between one-dimensional sequence and three-dimensional structural data in a convenient two-dimensional format. TopDraw is a simple, freely available TCL/Tk based drawing program designed specifically for the production of publication quality topology cartoons in a style commonly presented by structural biologists.nnnAVAILABILITYnTopDraw is freely available under the terms of the GNU General Public License. It can be downloaded from http://stein.bioch.dundee.ac.uk/~charlie/scripts/topdraw.html.

Crystal structure of Trypanosoma cruzi trypanothione reductase in complex with trypanothione, and the structure-based discovery of new natural product inhibitors.

BACKGROUNDnTrypanothione reductase (TR) helps to maintain an intracellular reducing environment in trypanosomatids, a group of protozoan parasites that afflict humans and livestock in tropical areas. This protective function is achieved via reduction of polyamine-glutathione conjugates, in particular trypanothione. TR has been validated as a chemotherapeutic target by molecular genetics methods. To assist the development of new therapeutics, we have characterised the structure of TR from the pathogen Trypanosoma cruzi complexed with the substrate trypanothione and have used the structure to guide database searches and molecular modelling studies.nnnRESULTSnThe TR-trypanothione-disulfide structure has been determined to 2.4 A resolution. The chemical interactions involved in enzyme recognition and binding of substrate can be inferred from this structure. Comparisons with the related mammalian enzyme, glutathione reductase, explain why each enzyme is so specific for its own substrate. A CH***O hydrogen bond can occur between the active-site histidine and a carbonyl of the substrate. This interaction contributes to enzyme specificity and mechanism by producing an electronic induced fit when substrate binds. Database searches and molecular modelling using the substrate as a template and the active site as receptor have identified a class of cyclic-polyamine natural products that are novel TR inhibitors.nnnCONCLUSIONSnThe structure of the TR-trypanothione enzyme-substrate complex provides details of a potentially valuable drug target. This information has helped to identify a new class of enzyme inhibitors as novel lead compounds worthy of further development in the search for improved medicines to treat a range of parasitic infections.

High-resolution crystal structure of Trypanosoma brucei UDP-galactose 4′-epimerase: a potential target for structure-based development of novel trypanocides

The crystal structure of UDP-galactose 4-epimerase from the protozoan parasite Trypanosoma brucei in complex with the cofactor NAD(+) and a fragment of the substrates, UDP, has been determined at 2.0 A resolution (1 A = 0.1 nm). This enzyme, recently proven to be essential for this pathogenic parasite, shares 33% sequence identity with the corresponding enzyme in the human host. Structural comparisons indicate that many of the protein-ligand interactions are conserved between the two enzymes. However, in the UDP-binding pocket there is a non-conservative substitution from Gly237 in the human enzyme to Cys266 in the T. brucei enzyme. Such a significant difference could be exploited by the structure-based design of selective inhibitors using the structure of the trypanosomatid enzyme as a template.

Specificity of the Trypanothione-Dependent Leishmania Major Glyoxalase I: Structure and Biochemical Comparison with the Human Enzyme.

Trypanothione replaces glutathione in defence against cellular damage caused by oxidants, xenobiotics and methylglyoxal in the trypanosomatid parasites, which cause trypanosomiasis and leishmaniasis. In Leishmania major, the first step in methylglyoxal detoxification is performed by a trypanothione‐dependent glyoxalase I (GLO1) containing a nickel cofactor; all other characterized eukaryotic glyoxalases use zinc. In kinetic studies L.u2003major and human enzymes were active with methylglyoxal derivatives of several thiols, but showed opposite substrate selectivities: N1‐glutathionylspermidine hemithioacetal is 40‐fold better with L.u2003major GLO1, whereas glutathione hemithioacetal is 300‐fold better with human GLO1. Similarly, S‐4‐bromobenzylglutathionylspermidine is a 24‐fold more potent linear competitive inhibitor of L.u2003major than human GLO1 (Kis of 0.54u2003µM and 12.6u2003µM, respectively), whereas S‐4‐bromobenzylglutathione is >u200a4000‐fold more active against human than L.u2003major GLO1 (Kis of 0.13u2003µM and >u200a500u2003µM respectively). The crystal structure of L.u2003major GLO1 reveals differences in active site architecture to both human GLO1 and the nickel‐dependent Escherichia coli GLO1, including increased negative charge and hydrophobic character and truncation of a loop that may regulate catalysis in the human enzyme. These differences correlate with the differential binding of glutathione and trypanothione‐based substrates, and thus offer a route to the rational design of L.u2003major‐specific GLO1 inhibitors.

Structure of a tetragonal crystal form of Escherichia coli 2-C-methyl-D-erythritol 4-phosphate cytidylyltransferase

2-C-Methyl-D-erythritol 4-phosphate cytidylyltransferase is an essential enzyme in the mevalonate-independent pathway of isoprenoid biosynthesis. The structure of a tetragonal crystal form has been solved by molecular replacement and refined to 2.4 A resolution. Structure and sequence comparisons suggest that the enzyme is a suitable target for a structure-based approach to the development of novel broad-spectrum antibiotics. However, the absence of ligands in the enzyme active site together with the moderate resolution of the structure indicates that this tetragonal crystal form is inferior to that of a previously reported highly ordered monoclinic form [Richard et al. (2001), Nature Struct. Biol. 8, 641-647].

The structure of plastocyanin from the cyanobacterium Phormidium laminosum.

The crystal structure of the blue copper protein plastocyanin from the cyanobacterium Phormidium laminosum has been solved and refined using 2.8 A X--ray data. P. laminosum plastocyanin crystallizes in space group P43212 with unit-cell dimensions a = 86.57, c = 91.47 A and with three protein molecules per asymmetric unit. The final residual R is 19.9%. The structure was solved using molecular replacement with a search model based on the crystal structure of a close homologue, Anabaena variabilis plastocyanin (66% sequence identity). The molecule of P. laminosum plastocyanin has 105 amino-acid residues. The single Cu atom is coordinated by the same residues - two histidines, a cysteine and a methionine - as in other plastocyanins. In the crystal structure, the three molecules of the asymmetric unit are related by a non-crystallographic threefold axis. A Zn atom lies between each pair of neighbouring molecules in this ensemble, being coordinated by a surface histidine residue of one molecule and by two aspartates of the other.

The crystal structure of a plant 2C‐methyl‐D‐erythritol 4‐phosphate cytidylyltransferase exhibits a distinct quaternary structure compared to bacterial homologues and a possible role in feedback regulation for cytidine monophosphate

The homodimeric 2C‐methyl‐d‐erythritol 4‐phosphate cytidylyltransferase contributes to the nonmevalonate pathway of isoprenoid biosynthesis. The crystal structure of the catalytic domain of the recombinant enzyme derived from the plant Arabidopsisu2003thaliana has been solved by molecular replacement and refined to 2.0u2003Å resolution. The structure contains cytidine monophosphate bound in the active site, a ligand that has been acquired from the bacterial expression system, and this observation suggests a mechanism for feedback regulation of enzyme activity. Comparisons with bacterial enzyme structures, in particular the enzyme from Escherichiau2003coli, indicate that whilst individual subunits overlay well, the arrangement of subunits in each functional dimer is different. That distinct quaternary structures are available, in conjunction with the observation that the protein structure contains localized areas of disorder, suggests that conformational flexibility may contribute to the function of this enzyme.

Crystallization and preliminary X-ray diffraction studies of recombinant Escherichia coli 4-­diphosphocytidyl-2-C-methyl-d-erythritol synthetase

Diphosphocytidyl-methylerythritol (DPCME) synthetase is involved in the mevalonate-independent pathway of isoprenoid biosynthesis, where it catalyses the formation of 4-diphosphocytidyl-2-C-methyl-D-erythritol from 2-C-methyl-D-erythritol 4-phosphate and CTP. The Escherichia coli enzyme has been cloned, expressed in high yield, purified and crystallized. Elongated tetragonal prismatic crystals grown by the hanging-drop vapour-diffusion method using polyethylene glycol (PEG) 4000 as the precipitant belong to space group P4(1)2(1)2 (or P4(3)2(1)2), with unit-cell parameters a = b = 73.60, c = 175.56 A. Diffraction data have been recorded to 2.4 A resolution using synchrotron radiation.

Crystallization and preliminary X-ray analysis of Leishmania major glyoxalase I

Glyoxalase I (GLO1) is a putative drug target for trypanosomatids, which are pathogenic protozoa that include the causative agents of leishmaniasis. Significant sequence and functional differences between Leishmania major and human GLO1 suggest that it may make a suitable template for rational inhibitor design. L. major GLO1 was crystallized in two forms: the first is extremely disordered and does not diffract, while the second, an orthorhombic form, produces diffraction to 2.0 A. Molecular-replacement calculations indicate that there are three GLO1 dimers in the asymmetric unit, which take up a helical arrangement with their molecular dyads arranged approximately perpendicular to the c axis. Further analysis of these data are under way.