A divergent external loop confers antagonistic activity on floral regulators FT and TFL1.

The Arabidopsis genes FT and TERMINAL FLOWER1 (TFL1) encode related proteins with similarity to human Raf kinase inhibitor protein. FT, and likely also TFL1, is recruited to the promoters of floral genes through interaction with FD, a bZIP transcription factor. FT, however, induces flowering, while TFL1 represses flowering. Residues responsible for the opposite activities of FT and TFL1 were mapped by examining plants that overexpress chimeric proteins. A region important in vivo localizes to a 14-amino-acid segment that evolves very rapidly in TFL1 orthologs, but is almost invariant in FT orthologs. Crystal structures show that this segment forms an external loop of variable conformation. The only residue unambiguously distinguishing the FT and TFL1 loops makes a hydrogen bond with a residue near the entrance of a potential ligand-binding pocket in TFL1, but not in FT. This pocket is contacted by a C-terminal peptide, which also contributes to the opposite FT and TFL1 activities. In combination, these results identify a molecular surface likely to be recognized by FT- and/or TFL1-specific interactors.

Identification and activity of a series of azole-based compounds with lactate dehydrogenase-directed anti-malarial activity.

Plasmodium falciparum, the causative agent of malaria, relies extensively on glycolysis coupled with homolactic fermentation during its blood-borne stages for energy production. Selective inhibitors of the parasite lactate dehydrogenase (LDH), central to NAD(+) regeneration, therefore potentially provide a route to new antimalarial drugs directed against a novel molecular target. A series of heterocyclic, azole-based compounds are described that preferentially inhibit P. falciparum LDH at sub-micromolar concentrations, typically at concentrations about 100-fold lower than required for human lactate dehydrogenase inhibition. Crystal structures show these competitive inhibitors form a network of interactions with amino acids within the active site of the enzyme, stacking alongside the nicotinamide ring of the NAD(+) cofactor. These compounds display modest activity against parasitized erythrocytes, including parasite strains with known resistance to existing anti-malarials and against Plasmodium berghei in BALB/c mice. Initial toxicity data suggest the azole derivatives have generally low cytotoxicity, and preliminary pharmoco-kinetic data show favorable bioavailability and circulation times. These encouraging results suggest that further enhancement of these structures may yield candidates suitable for consideration as new therapeutics for the treatment of malaria. In combination these studies also provide strong support for the validity of targeting the Plasmodium glycolytic pathway and, in particular, LDH in the search for novel anti-malarials.