The Small GTPases in Fungal Signaling Conservation and Function

Monomeric GTPases, which belong to the Ras superfamily, are small proteins involved in many biological processes. They are fine-tuned regulated by guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). Several families have been identified in organisms from different kingdoms. Overall, the most studied families are Ras, Rho, Rab, Ran, Arf, and Miro. Recently, a new family named Big Ras GTPases was reported. As a general rule, the proteins of all families have five characteristic motifs (G1–G5), and some specific features for each family have been described. Here, we present an exhaustive analysis of these small GTPase families in fungi, using 56 different genomes belonging to different phyla. For this purpose, we used distinct approaches such as phylogenetics and sequences analysis. The main functions described for monomeric GTPases in fungi include morphogenesis, secondary metabolism, vesicle trafficking, and virulence, which are discussed here. Their participation during fungus–plant interactions is reviewed as well.

Selective targeting of the BRG/PB1 bromodomains impairs embryonic and trophoblast stem cell maintenance

Mammalian SWI/SNF [also called Brg/Brahma-associated factors (BAFs)] are evolutionarily conserved chromatin-remodeling complexes regulating gene transcription programs during development and stem cell differentiation. BAF complexes contain an ATP (adenosine 5'-triphosphate)-driven remodeling enzyme (either BRG1 or BRM) and multiple protein interaction domains including bromodomains, an evolutionary conserved acetyl lysine-dependent protein interaction motif that recruits transcriptional regulators to acetylated chromatin. We report a potent and cell active protein interaction inhibitor, PFI-3, that selectively binds to essential BAF bromodomains. The high specificity of PFI-3 was achieved on the basis of a novel binding mode of a salicylic acid head group that led to the replacement of water molecules typically maintained in other bromodomain inhibitor complexes. We show that exposure of embryonic stem cells to PFI-3 led to deprivation of stemness and deregulated lineage specification. Furthermore, differentiation of trophoblast stem cells in the presence of PFI-3 was markedly enhanced. The data present a key function of BAF bromodomains in stem cell maintenance and differentiation, introducing a novel versatile chemical probe for studies on acetylation-dependent cellular processes controlled by BAF remodeling complexes.