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CRM1 (also known as XPO1 and exportin 1) mediates nuclear export of hundreds of proteins through the recognition of the leucine-rich nuclear export signal (LR-NES). Here we present the 2.9 Å structure of CRM1 bound to snurportin 1 (SNUPN). Snurportin 1 binds CRM1 in a bipartite manner by means of an amino-terminal LR-NES and its nucleotide-binding domain. The LR-NES is a combined α-helical-extended structure that occupies a hydrophobic groove between two CRM1 outer helices. The LR-NES interface explains the consensus hydrophobic pattern, preference for intervening electronegative residues and inhibition by leptomycin B. The second nuclear export signal epitope is a basic surface on the snurportin 1 nucleotide-binding domain, which binds an acidic patch on CRM1 adjacent to the LR-NES site. Multipartite recognition of individually weak nuclear export signal epitopes may be common to CRM1 substrates, enhancing CRM1 binding beyond the generally low affinity LR-NES. Similar energetic construction is also used in multipartite nuclear localization signals to provide broad substrate specificity and rapid evolution in nuclear transport., Nuclear localization and export signals (NLSs and NESS) are recognized by karyopherin-β (Kap-β, also known as importin and exportin) proteins to direct macromolecules in and out of the nucleus (1-4). [...]

Ornithine decarboxylase (ODC) is an obligate homodimer that catalyzes the pyridoxal 5'-phosphate-dependent decarboxylation of L-ornithine to putrescine in polyamine biosynthesis. It is reported that ODC is investigated as a therapeutic target for a number of proliferative diseases and has proved to be an effective target in the treatment of African sleeping sickness, a fatal tropical disease.

The mutation of retinoid X receptor (RXR) and identification of an orthogonal ligand-receptor pair are described. The compounds activate mutant receptors effectively and hence it is shown that the inactive 'near drugs' developed during research programs are a reservoir of chemical potential that can be exploited in conjunction with mutant proteins that possess altered specificities.

Results support that long-range energetic coupling of interface residues to the active site is necessary for ornithine decarboxylase function. Further, the catalytic function of the enzyme is governed by the enzyme's dimer interface, enabling access by small molecules to the enzyme interface without energy barriers.

Results show that formation of putrescine by ornithine decarboxylase is dependent on the alpha-carbon protonation as indicated by the mutation of cysteine-360 residue of the enzyme to alanine or serine. The rate-limiting step in the enzyme steady-state reaction involves Schiff base hydrolysis.

Results point out that Phe-397 promotes the decarboxylation step of the Trypanosoma brucei ornithine decarboxylase via the binding of the enzyme to the carboxyl leaving group of L-Orn on the re face of the pyridoxal-5'-phosphate cofactor. By virtue of the localization of the leaving group in the buried side of the cofactor, the enzyme dcarboxylates by destabilizing the substrate carboxyl group.

Focuses on the Ornithine decarboxylase enzyme catalyst of biosynthesis of the polyamines. Mutagenesis of the dimer interface on the energetic contribution to the subunit association; Catalytic efficiency of the enzyme on mutations; Coupling of interface residues for enzyme function.

With no lysine (K) (WNK) kinases regulate epithelial ion transport in the kidney to maintain homeostasis of electrolyte concentrations and blood pressure. Chloride ion directly binds WNK kinases to inhibit autophosphorylation and activation. Changes in extracellular potassium are thought to regulate WNKs through changes in intracellular chloride. Prior studies demonstrate that in some distal nephron epithelial cells, intracellular potassium changes with chronic low- or high-potassium diet. We, therefore, investigated whether potassium regulates WNK activity independent of chloride. We found decreased activity of Drosophila WNK and mammalian WNK3 and WNK4 in fly Malpighian (renal) tubules bathed in high extracellular potassium, even when intracellular chloride was kept constant at either ∼13 mM or 26 mM. High extracellular potassium also inhibited chloride-insensitive mutants of WNK3 and WNK4. High extracellular rubidium was also inhibitory and increased tubule rubidium. The Na + /K + -ATPase inhibitor, ouabain, which is expected to lower intracellular potassium, increased tubule Drosophila WNK activity. In vitro, potassium increased the melting temperature of Drosophila WNK, WNK1, and WNK3 kinase domains, indicating ion binding to the kinase. Potassium inhibited in vitro autophosphorylation of Drosophila WNK and WNK3, and also inhibited WNK3 and WNK4 phosphorylation of their substrate, Ste20-related proline/alanine-rich kinase (SPAK). The greatest sensitivity of WNK4 to potassium occurred in the range of 80-180 mM, encompassing physiological intracellular potassium concentrations. Together, these data indicate chloride-independent potassium inhibition of Drosophila and mammalian WNK kinases through direct effects of potassium ion on the kinase.

Parasite infections affect billions of humans world-wide, yet the current drugs available for the treatment of many parasitic diseases are either inadequate, or compromised by the development of resistance. Validation of a drug target is an important step in the development of new drugs. Target validation encompasses verifying that a target is primarily responsible for the therapeutic activity of a proven drug, or demonstrating the essential nature of a putative drug target in a parasite, and the capacity for selective inhibition of that target in vivo. Selective toxicity may be achieved by taking advantage of unique parasite biology or biochemistry, or by utilizing differences in metabolism or import. The essential nature of a target may be demonstrated by the correlation of the chemical or genetic reduction of target activity with the loss of parasite growth or virulence. Rescue experiments may demonstrate the single nature of a target. Ultimately, a target must be validated in vivo.