Evolution and Multiplicity of Arginine Decarboxylases in Polyamine Biosynthesis and Essential Role in Bacillus subtilis Biofilm Formation

Arginine decarboxylases (ADCs; EC 4.1.1.19) from four different protein fold families are important for polyamine biosynthesis in bacteria, archaea, and plants. Biosynthetic alanine racemase fold (AR-fold) ADC is widespread in bacteria and plants. We report the discovery and characterization of an ancestral form of the AR-fold ADC in the bacterial Chloroflexi and Bacteroidetes phyla. The ancestral AR-fold ADC lacks a large insertion found in Escherichia coli and plant AR-fold ADC and is more similar to the lysine biosynthetic enzyme meso-diaminopimelate decarboxylase, from which it has evolved. An E. coli acid-inducible ADC belonging to the aspartate aminotransferase fold (AAT-fold) is involved in acid resistance but not polyamine biosynthesis. We report here that the acid-inducible AAT-fold ADC has evolved from a shorter, ancestral biosynthetic AAT-fold ADC by fusion of a response regulator receiver domain protein to the N terminus. Ancestral biosynthetic AAT-fold ADC appears to be limited to firmicute bacteria. The phylogenetic distribution of different forms of ADC distinguishes bacteria from archaea, euryarchaeota from crenarchaeota, double-membraned from single-membraned bacteria, and firmicutes from actinobacteria. Our findings extend to eight the different enzyme forms carrying out the activity described by EC 4.1.1.19. ADC gene clustering reveals that polyamine biosynthesis employs diverse and exchangeable synthetic modules. We show that in Bacillus subtilis, ADC and polyamines are essential for biofilm formation, and this appears to be an ancient, evolutionarily conserved function of polyamines in bacteria. Also of relevance to human health, we found that arginine decarboxylation is the dominant pathway for polyamine biosynthesis in human gut microbiota.     

Starch: the need for improved quality or quantity--an overview

Starch is one of the most important plant products to man. It is an essential component of food providing a large proportion of the daily calorific intake and is important in non-food uses such as in adhesives. However, while much is known about the chemistry and pathways of synthesis for starch, there are major gaps in this knowledge so that it is not possible to modify the quantity or quality of starch produced by plants in a predictable way. While yield has improved markedly over the last century it is no longer improving faster than the growth in population and, at the same time, farmers' incomes in Europe have been falling, especially in the UK. Thus, production, even in Europe, is not much greater than demand. In the western world an increasing amount of the harvested crop is processed and, therefore, the quality of the raw product becomes an increasingly important issue. There is, therefore, an increasing need to combine the modern mathematical modelling tools with modern biochemical tools and the modern science of genomics.     

Kinda baboons (Papio kindae) and grayfoot chacma baboons (P. ursinus griseipes) hybridize in the Kafue river valley, Zambia

The ranges of small kinda (Papio kindae) and much larger grayfooted chacma (P. ursinus griseipes) baboons adjoin in the Kafue National Park, Zambia. In a visual survey of baboons at 48 sites in the Kafue River drainage we found that, contrary to previous reports, groups at the species interface near the town of Ngoma are phenotypically diverse and presumably formed by multigenerational hybridization. Mitochondrial and/or Y-chromosome genetic markers from fecal samples (N=164) collected at 29 sites support this conclusion. Groups with phenotypic signs of a history of hybridization also had taxon-specific mitochondria and Y-haplotypes from both parental species. Although the distribution of mitochondrial haplotypes largely mirrored that of external phenotypes, a significant proportion of male specimens from grayfoot as well as hybrid groups carried kinda Y-chromosomes, and kinda Y-chromosomes were involved in all observed cases of mitochondrial/Y-chromosome discordance. These observations are consistent with, though they do not prove, a population history in which the range of chacmas and the hybrid zone have advanced at the expense of the kinda range. They also suggest that, unexpectedly, kinda male×chacma female matings are much more common than the reciprocal cross in the ancestry of hybrids. We suggest that distinctive male kinda behavior and the "juvenile" appearance of kinda baboons of both sexes, perhaps combined with obstetric difficulties of a small kinda female carrying the large offspring of a chacma male, may account for this bias.     

Selective down-regulation of AT2 receptors in uterine arteries from pregnant ewes given 24-h intravenous infusions of angiotensin II

Previously, we showed that uterine arteries from late gestation pregnant ewes infused intravenously with angiotensin II (Ang II) for 24 h, displayed heightened responsiveness to Ang II in vitro. Furthermore, we found that a small population of ewes with a "preeclampsia-like" disorder also displayed this. Therefore, we have investigated the density and affinity of Ang II receptor subtypes in the uterine arteries from these groups. Ang II receptor binding was measured using 125I [Sar1Ile8] Ang II. Proportions of AT1 and AT2 receptors were determined by inhibiting 125I [Sar1Ile8] Ang II with losartan (AT1 antagonist) or PD 123319 (AT2 antagonist). Uterine arteries from 24-h Ang II-infused ewes had a lower proportion of AT2 receptors (56.2+/-2.3%) than control (saline-infused) ewes (84.1+/-1.0%; P<0.05). The density of AT2 receptors was reduced (P<0.05) while the density of AT1 receptors was not different. Thus, 24-h infusions of Ang II selectively down-regulated AT2 receptors in the uterine artery, resulting in heightened Ang II reactivity. By contrast, the binding properties of Ang II receptor subtypes in uterine arteries from ewes with the "preeclampsia-like" disorder were not different from control ewes.     

Fyn Tyrosine Kinase Increases Apolipoprotein E Receptor 2 Levels and Phosphorylation

Apolipoprotein E Receptor 2 (ApoER2) and the tyrosine kinase Fyn are both members of the Reelin pathway, a signaling pathway essential for the laminar formation of the cortex during development and proper dendritic spine density and long-term potential (LTP) in the adult brain. In the presence of extracellular Reelin, ApoER2 binds the intracellular protein Dab1, an adaptor protein that is phosphorylated by Fyn. However, direct interactions between ApoER2 and Fyn are not well defined. Here, we show that total levels of ApoER2 and surface levels of ApoER2 are increased by active Fyn. Via a separate mechanism, ApoER2 is also phosphorylated by Fyn, an event that peaks in the postnatal cortex at day 5 and can occur at multiple ApoER2 tyrosine residues. Dab1 is also involved in this phosphorylation, promoting the phosphorylation of ApoER2 by Fyn when it is itself phosphorylated. These results elucidate some of the intracellular mechanisms that give rise to a functional Reelin pathway.