Structure and mechanism of the mammalian fructose transporter GLUT5.

The altered activity of the fructose transporter GLUT5, an isoform of the facilitated-diffusion glucose transporter family, has been linked to disorders such as type 2 diabetes and obesity. GLUT5 is also overexpressed in certain tumour cells, and inhibitors are potential drugs for these conditions. Here we describe the crystal structures of GLUT5 from Rattus norvegicus and Bos taurus in open outward- and open inward-facing conformations, respectively. GLUT5 has a major facilitator superfamily fold like other homologous monosaccharide transporters. On the basis of a comparison of the inward-facing structures of GLUT5 and human GLUT1, a ubiquitous glucose transporter, we show that a single point mutation is enough to switch the substrate-binding preference of GLUT5 from fructose to glucose. A comparison of the substrate-free structures of GLUT5 with occluded substrate-bound structures of Escherichia coli XylE suggests that, in addition to global rocker-switch-like re-orientation of the bundles, local asymmetric rearrangements of carboxy-terminal transmembrane bundle helices TM7 and TM10 underlie a 'gated-pore' transport mechanism in such monosaccharide transporters.

Discovery and SAR study of 2-(4-pyridylamino)thieno[3,2-d]pyrimidin-4(3H)-ones as soluble and highly potent PDE7 inhibitors.

The discovery and SAR study of a new series of soluble and highly potent phosphodiesterase (PDE) 7 inhibitors are described herein. We explored a new lead compound with improved solubility, which led to the discovery of a 2-(4-pyridylamino)thieno[3,2-d]pyrimidin-4(3H)-one series. The introduction of 3-piperidines at the 7-position resulted in the significant enhancement of PDE7 activity. In particular, compound 32 also showed strong PDE7 inhibitory activity; good selectivity against PDE3, 4, and 5; and good aqueous solubility.

2-(Isopropylamino)thieno[3,2-d]pyrimidin-4(3H)-one derivatives as selective phosphodiesterase 7 inhibitors with potent in vivo efficacy.

A new series of thienopyrimidinones is synthesized and evaluated as selective phosphodiesterase 7 (PDE7) inhibitors for the treatment of inflammatory diseases. The modification of the substituents on thienopyrimidinone revealed that an isopropylamino group at the 2-position was favorable for aqueous solubility. The introduction of 3-pyrrolidines at the 7-position resulted in good solubility, highly potent activity, and good PDE7 selectivity. Among the synthesized compounds, compound 46 exhibited the greatest inhibition of ear edema in a phorbol ester-induced mouse model.

Structure of Spo0M, a sporulation-control protein from Bacillus subtilis.

Spo0M is a sporulation-control protein that is thought to play an essential role in the early stage of endospore formation. While little is known about the functions of Spo0M, a recent phylogenetic study suggests that, based on its amino-acid sequence, Spo0M might belong to the arrestin clan. The crystal structure of the Spo0M protein was determined at a resolution of 2.3 Å. Ten amino acids at the end of the N-terminus were removed to improve the thermal stability of the purified Spo0M protein and the crystal structure of Spo0M was determined by SAD. Spo0M has a well conserved N-terminal domain with an arrestin-like fold, which consists of a ß-strand sandwich structure. Surprisingly, the C-terminal domain of Spo0M, which has no structural homology to arrestin-clan proteins, bears significant structural similarity to the FP domain of the human PI31 protein. In addition, Spo0M harbours a potential polar-core structure connecting the N- and C-terminal domains with several salt bridges, as seen in the crystal structures of arrestin and VPS26. The structure reported here constitutes the first structural information on a bacterial protein that shares significant structural homology to members of the arrestin clan and the FP domain.

Discovery of 2-(cyclopentylamino)thieno[3,2-d]pyrimidin-4(3H)-one derivatives as a new series of potent phosphodiesterase 7 inhibitors.

The discovery of a new series of potent phosphodiesterase 7 (PDE7) inhibitors is described. Novel thieno[3,2-d]pyrimidin-4(3H)-one hit compounds were identified from our chemical library. Preliminary modifications of the hit compounds were performed, resulting in the discovery of a fragment-sized compound (10) with highly improved ligand efficiency. Compound design was guided by structure-activity relationships and computational modeling. The 6-substituted derivatives of the thienopyrimidinone showed diminished activity and enzyme selectivity. However, synthesis of the 7-substituted derivatives resulted in the discovery of 28e, a desirable lead compound that selectively inhibits PDE7 with single-digit nanomolar potency while displaying potent cellular efficacy.

Benchmarking membrane protein detergent stability for improving throughput of high-resolution X-ray structures.

Obtaining well-ordered crystals is a major hurdle to X-ray structure determination of membrane proteins. To facilitate crystal optimization, we investigated the detergent stability of 24 eukaryotic and prokaryotic membrane proteins, predominantly transporters, using a fluorescent-based unfolding assay. We have benchmarked the stability required for crystallization in small micelle detergents, as they are statistically more likely to lead to high-resolution structures. Using this information, we have been able to obtain well-diffracting crystals for a number of sodium and proton-dependent transporters. By including in the analysis seven membrane proteins for which structures are already known, AmtB, GlpG, Mhp1, GlpT, EmrD, NhaA, and LacY, it was further possible to demonstrate an overall trend between protein stability and structural resolution. We suggest that by monitoring membrane protein stability with reference to the benchmarks described here, greater efforts can be placed on constructs and conditions more likely to yield high-resolution structures.

Tricks of the trade used to accelerate high-resolution structure determination of membrane proteins.

The rate at which X-ray structures of membrane proteins are solved is on a par with that of soluble proteins in the late 1970s. There are still many obstacles facing the membrane protein structural community. Recently, there have been several technical achievements in the field that have started to dramatically accelerate structural studies. Here, we summarize these so-called 'tricks-of-the-trade' and include case studies of several mammalian transporters.

GFP-based optimization scheme for the overexpression and purification of eukaryotic membrane proteins in Saccharomyces cerevisiae.

It is often difficult to produce eukaryotic membrane proteins in large quantities, which is a major obstacle for analyzing their biochemical and structural features. To date, yeast has been the most successful heterologous overexpression system in producing eukaryotic membrane proteins for high-resolution structural studies. For this reason, we have developed a protocol for rapidly screening and purifying eukaryotic membrane proteins in the yeast Saccharomyces cerevisiae. Using this protocol, in 1 week many genes can be rapidly cloned by homologous recombination into a 2 micro GFP-fusion vector and their overexpression potential determined using whole-cell and in-gel fluorescence. The quality of the overproduced eukaryotic membrane protein-GFP fusions can then be evaluated over several days using confocal microscopy and fluorescence size-exclusion chromatography (FSEC). This protocol also details the purification of targets that pass our quality criteria, and can be scaled up for a large number of eukaryotic membrane proteins in either an academic, structural genomics or commercial environment.