Stephen R. Wasserman

Crystal structure of the human PRMT5:MEP50 complex

Protein arginine methyltransferases (PRMTs) play important roles in several cellular processes, including signaling, gene regulation, and transport of proteins and nucleic acids, to impact growth, differentiation, proliferation, and development. PRMT5 symmetrically di-methylates the two-terminal ω-guanidino nitrogens of arginine residues on substrate proteins. PRMT5 acts as part of a multimeric complex in concert with a variety of partner proteins that regulate its function and specificity. A core component of these complexes is the WD40 protein MEP50/WDR77/p44, which mediates interactions with binding partners and substrates. We have determined the crystal structure of human PRMT5 in complex with MEP50 (methylosome protein 50), bound to an S-adenosylmethionine analog and a peptide substrate derived from histone H4. The structure of the surprising hetero-octameric complex reveals the close interaction between the seven-bladed β-propeller MEP50 and the N-terminal domain of PRMT5, and delineates the structural elements of substrate recognition.

SGX523 is an exquisitely selective, ATP-competitive inhibitor of the MET receptor tyrosine kinase with antitumor activity in vivo

The MET receptor tyrosine kinase has emerged as an important target for the development of novel cancer therapeutics. Activation of MET by mutation or gene amplification has been linked to kidney, gastric, and lung cancers. In other cancers, such as glioblastoma, autocrine activation of MET has been demonstrated. Several classes of ATP-competitive inhibitor have been described, which inhibit MET but also other kinases. Here, we describe SGX523, a novel, ATP-competitive kinase inhibitor remarkable for its exquisite selectivity for MET. SGX523 potently inhibited MET with an IC50 of 4 nmol/L and is >1,000-fold selective versus the >200-fold selectivity of other protein kinases tested in biochemical assays. Crystallographic study revealed that SGX523 stabilizes MET in a unique inactive conformation that is inaccessible to other protein kinases, suggesting an explanation for the selectivity. SGX523 inhibited MET-mediated signaling, cell proliferation, and cell migration at nanomolar concentrations but had no effect on signaling dependent on other protein kinases, including the closely related RON, even at micromolar concentrations. SGX523 inhibition of MET in vivo was associated with the dose-dependent inhibition of growth of tumor xenografts derived from human glioblastoma and lung and gastric cancers, confirming the dependence of these tumors on MET catalytic activity. Our results show that SGX523 is the most selective inhibitor of MET catalytic activity described to date and is thus a useful tool to investigate the role of MET kinase in cancer without the confounding effects of promiscuous protein kinase inhibition. [Mol Cancer Ther 2009;8(12):3181–90]

Structures of a minimal human CFTR first nucleotide- binding domain as a monomer, head-to-tail homodimer, and pathogenic mutant

Upon removal of the regulatory insert (RI), the first nucleotide binding domain (NBD1) of human cystic fibrosis transmembrane conductance regulator (CFTR) can be heterologously expressed and purified in a form that remains stable without solubilizing mutations, stabilizing agents or the regulatory extension (RE). This protein, NBD1 387-646(Delta405-436), crystallizes as a homodimer with a head-to-tail association equivalent to the active conformation observed for NBDs from symmetric ATP transporters. The 1.7-A resolution X-ray structure shows how ATP occupies the signature LSGGQ half-site in CFTR NBD1. The DeltaF508 version of this protein also crystallizes as a homodimer and differs from the wild-type structure only in the vicinity of the disease-causing F508 deletion. A slightly longer construct crystallizes as a monomer. Comparisons of the homodimer structure with this and previously published monomeric structures show that the main effect of ATP binding at the signature site is to order the residues immediately preceding the signature sequence, residues 542-547, in a conformation compatible with nucleotide binding. These residues likely interact with a transmembrane domain intracellular loop in the full-length CFTR channel. The experiments described here show that removing the RI from NBD1 converts it into a well-behaved protein amenable to biophysical studies yielding deeper insights into CFTR function.

Giant magnetoresistance at 300 K in single crystals of La0.65(PbCa)0.35MnO3

Giant magnetoresistance (GMR) at 300 K and 5.5 T with ΔR/R(0)=74% was observed in single crystals of La0.65(PbCa)0.35MnO3. The maximum GMR occurs exactly at the ferromagnetic–paramagnetic phase transition temperature (Tc). For T<Tc, the R(T) curve is closely related to the M(T) curve. A sign change in the curvatures of R(H) curves below and above Tc has been observed, indicating that two different mechanisms are responsible for the magnetic scatterings of the carriers in two separate temperature regions.

Monolayers of 11-Trichlorosilylundecyl Thioacetate: A System that Promotes Adhesion Between Silicon Dioxide and Evaporated Gold

Abstract : This chapter describes the use of sulfur-containing organic monolayers to improve the adhesion of gold to silicon substrates having a native silicon dioxide surface layer. Gold adheres to clean silicon, but not to silicon dioxide. The affinity of gold toward silicon dioxide can be improved by coating with chromium or titanium films or by adding interlayers containing fluoride salts. Bombardment of gold-covered silicon dioxide with electrons or heavy ions also enhances adhesion. Thin covalently-bonded alkylsiloxane films containing amines or epoxides improve the adherence of gold to glass. Here we demonstrate that covering a Silicon/Silicon dioxide substrate with a covalently attached organic monolayer film containing thiol groups (and possibly disulfides derived from them) or thioacetate groups improves the adhesion of gold to the substrate.

Rapid-access, high-throughput synchrotron crystallography for drug discovery

Synchrotron X-ray sources provide the highest quality crystallographic data for structure-guided drug design. In general, industrial utilization of such sources has been intermittent and occasionally limited. The Lilly Research Laboratories Collaborative Access Team (LRL-CAT) beamline provides a unique alternative to traditional synchrotron use by pharmaceutical and biotechnology companies. Crystallographic experiments at LRL-CAT and the results therefrom are integrated directly into the drug discovery process, permitting structural data, including screening of fragment libraries, to be routinely and rapidly used on a daily basis as part of pharmaceutical lead discovery and optimization. Here we describe how LRL-CAT acquires and disseminates the results from protein crystallography to maximize their impact on the development of new potential medicines.

Structure of the C-terminal domain of Saccharomyces cerevisiae Nup133, a component of the nuclear pore complex

Nuclear pore complexes (NPCs), responsible for the nucleo-cytoplasmic exchange of proteins and nucleic acids, are dynamic macromolecular assemblies forming an eight-fold symmetric co-axial ring structure. Yeast (Saccharomyces cerevisiae) NPCs are made up of at least 456 polypeptide chains of {approx}30 distinct sequences. Many of these components (nucleoporins, Nups) share similar structural motifs and form stable subcomplexes. We have determined a high-resolution crystal structure of the C-terminal domain of yeast Nup133 (ScNup133), a component of the heptameric Nup84 subcomplex. Expression tests yielded ScNup133(944-1157) that produced crystals diffracting to 1.9{angstrom} resolution. ScNup133(944-1157) adopts essentially an all {alpha}-helical fold, with a short two stranded {beta}-sheet at the C-terminus. The 11 {alpha}-helices of ScNup133(944-1157) form a compact fold. In contrast, the previously determined structure of human Nup133(934-1156) bound to a fragment of human Nup107 has its constituent {alpha}-helices are arranged in two globular blocks. These differences may reflect structural divergence among homologous nucleoporins.

Hydrolysis of uranium and thorium in surface-modified bentonite under hydrothermal conditions

Abstract The speciation of (UO 2 ) 2+ - and Th 4+ -exchanged bentonite clay samples was probed by X-ray absorption spectroscopy (XAS). Surface modification reactions using hydrophobic silanes were performed in order to ascertain the effects of excluding the free exchange of external water from the clay gallery. Hydrothermal conditions were used to mimic potential geologic conditions in a nuclear waste storage facility. Both the (UO 2 ) 2+ and Th 4+ samples showed evidence of polymeric hydrolysis products similar to the fluorite structure known for both UO 2 and ThO 2 .

Structural Underpinnings of Nitrogen Regulation by the Prototypical Nitrogen-Responsive Transcriptional Factor NrpR

Plants and microorganisms reduce environmental inorganic nitrogen to ammonium, which then enters various metabolic pathways solely via conversion of 2-oxoglutarate (2OG) to glutamate and glutamine. Cellular 2OG concentrations increase during nitrogen starvation. We recently identified a family of 2OG-sensing proteins--the nitrogen regulatory protein NrpR--that bind DNA and repress transcription of nitrogen assimilation genes. We used X-ray crystallography to determine the structure of NrpR regulatory domain. We identified the NrpR 2OG-binding cleft and show that residues predicted to interact directly with 2OG are conserved among diverse classes of 2OG-binding proteins. We show that high levels of 2OG inhibit NrpRs ability to bind DNA. Electron microscopy analyses document that NrpR adopts different quaternary structures in its inhibited 2OG-bound state compared with its active apo state. Our results indicate that upon 2OG release, NrpR repositions its DNA-binding domains correctly for optimal interaction with DNA thereby enabling gene repression.

Atomic structure of the nuclear pore complex targeting domain of a Nup116 homologue from the yeast, Candida glabrata

The nuclear pore complex (NPC), embedded in the nuclear envelope, is a large, dynamic molecular assembly that facilitates exchange of macromolecules between the nucleus and the cytoplasm. The yeast NPC is an eightfold symmetric annular structure composed of ∼456 polypeptide chains contributed by ∼30 distinct proteins termed nucleoporins. Nup116, identified only in fungi, plays a central role in both protein import and mRNA export through the NPC. Nup116 is a modular protein with N‐terminal “FG” repeats containing a Gle2p‐binding sequence motif and a NPC targeting domain at its C‐terminus. We report the crystal structure of the NPC targeting domain of Candida glabrata Nup116, consisting of residues 882–1034 [CgNup116(882–1034)], at 1.94 Å resolution. The X‐ray structure of CgNup116(882–1034) is consistent with the molecular envelope determined in solution by small‐angle X‐ray scattering. Structural similarities of CgNup116(882–1034) with homologous domains from Saccharomyces cerevisiae Nup116, S. cerevisiae Nup145N, and human Nup98 are discussed. Proteins 2012;