Mechanistic divergence between (4S,7R)-germacra-(1(10)E,5E)-dien-11-ol synthases from Dictyostelium purpureum and Streptomyces coelicolor

The enzyme mechanism of germacradienol synthase DpTPS9 from Dictyostelium purpureum has been studied by labelling experiments and site-directed mutagenesis, and is different to the mechanism of geosmin synthase SCO6073 from Streptomyces coelicolor.

An ancestral bacterial division system is widespread in eukaryotic mitochondria

Bacterial division initiates at the site of a contractile Z-ring composed of polymerized FtsZ. The location of the Z-ring in the cell is controlled by a system of three mutually antagonistic proteins, MinC, MinD, and MinE. Plastid division is also known to be dependent on homologs of these proteins, derived from the ancestral cyanobacterial endosymbiont that gave rise to plastids. In contrast, the mitochondria of model systems such asSaccharomyces cerevisiae, mammals, andArabidopsis thalianaseem to have replaced the ancestral α-proteobacterial Min-based division machinery with host-derived dynamin-related proteins that form outer contractile rings. Here, we show that the mitochondrial division system of these model organisms is the exception, rather than the rule, for eukaryotes. We describe endosymbiont-derived, bacterial-like division systems comprising FtsZ and Min proteins in diverse less-studied eukaryote protistan lineages, including jakobid and heterolobosean excavates, a malawimonad, stramenopiles, amoebozoans, a breviate, and an apusomonad. For two of these taxa, the amoebozoanDictyostelium purpureumand the jakobidAndalucia incarcerata, we confirm a mitochondrial localization of these proteins by their heterologous expression inSaccharomyces cerevisiae. The discovery of a proteobacterial-like division system in mitochondria of diverse eukaryotic lineages suggests that it was the ancestral feature of all eukaryotic mitochondria and has been supplanted by a host-derived system multiple times in distinct eukaryote lineages.

Endogenous cell surface lectin in Dictyostelium: quantitation, elution by sugar, and elicitation by divalent immunoglobulin.

The amount of total endogenous cellular and cell surface lectin in aggregating Dictyostelium purpureum was determined by a number of immunochemical techniques. The results show that of the 5 x 10(6) molecules of the lectin (called purpurin) per aggregating cell only about 2% (1 x 10(5) molecules) is present on the cell surface. Cell surface purpurin can be specially eluted by lactose, which indicates that it is held to the surface by its carbohydrate-binding site. The eluted purpurin is replaced on the cell surface within 45 min. Estimates of cell surface purpurin made by binding of specific immunoglobulin to the cells at 4 degrees C indicate that a much larger amount, about 1 x 10(6) molecules, becomes associated with the cell surface in the presence of this divalent ligand. In contrast, univalent antibody fragments do not have this effect.