Absolute reflexive retracts and absolute bipartite retracts

AbstractIt is a well-known phenomenon in the study of graph retractions that most results about absolute retracts in the class of bipartite (irreflexive) graphs have analogues about absolute retracts in the class of reflexive graphs, and vice versa. In this paper we make some observations that make the connection explicit. We develop four natural transformations between reflexive graphs and bipartite graphs which preserve the property of being an absolute retract, and allow us to derive results about absolute reflexive retracts from similar results about absolute bipartite retracts and conversely. Then we introduce generic notions that specialize to the appropriate concepts in both cases. This paves the way to a unified view of both theories, leading to absolute retracts of general (i.e., partially reflexive) graphs

Dynamic interaction in tropical Africa: IGCP-616Y and IGCP 646 projects and events

The scientific objectives and research program of the IGCP-646 project (2015–2018) cuts across many disciplines and includes various aspects of continental basement geology, resource exploration (mineral, water and hydrocarbons), geohazard mitigation, and climate change, all of which are of critical importance to developing countries, particularly in parts of West Africa where population pressures are on the rise. Considerable emphasis was placed on capacity building, creation of opportunities for young scientists to undertake higher degrees programs, knowledge transfer and training. The SIDA-funded “pilot project” IGCP-616Y (started in 2012), focused on three objects (i) crustal architecture, tectonic evolution and regional geology of Central Africa and the connection with NE Brazil; (ii) the Mesozoic continental rifting and breakup leading to a better integration of the onshore and offshore geology; (iii) clarification and quantification of the links between basement structures, neotectonics, climate change and landscape evolution. The IGCP-616Y and IGCP-646 projects consisted of over 250 researchers, from different countries. In the course of the projects, six annual meetings, four field trips/workshops, as well as several training sessions were organized. Here we provide a summary of the scientific targets of the projects and a summary of the organized activities

Recycling, clustering, and endocytosis jointly maintain PIN auxin carrier polarity at the plasma membrane

A combination of super-resolution microscopy in live cells and computational modeling provides new insights into the dynamic and interwoven mechanism that maintains the polar distribution of an important plant cargo

Dual lysine and N-terminal acetyltransferases reveal the complexity underpinning protein acetylation

Protein acetylation is a highly frequent protein modification. However, comparatively little is known about its enzymatic machinery. N-alpha-acetylation (NTA) and epsilon-lysine acetylation (KA) are known to be catalyzed by distinct families of enzymes (NATs andKATs, respectively), although the possibility that the sameGCN5-relatedN-acetyltransferase (GNAT) can perform both functions has been debated. Here, we discovered a new family of plastid-localizedGNATs, which possess a dual specificity. All characterizedGNATfamily members display a number of unique features. Quantitative mass spectrometry analyses revealed that these enzymes exhibit both distinctKAand relaxedNTAspecificities. Furthermore, inactivation ofGNAT2 leads to significantNTAorKAdecreases of several plastid proteins, while proteins of other compartments were unaffected. The data indicate that these enzymes have specific protein targets and likely display partly redundant selectivity, increasing the robustness of the acetylation processin vivo. In summary, this study revealed a new layer of complexity in the machinery controlling this prevalent modification and suggests that other eukaryoticGNATs may also possess these previously underappreciated broader enzymatic activities

Abstracts from the 8th International Conference on cGMP Generators, Effectors and Therapeutic Implications

This work was supported by a restricted research grant of Bayer AG

Use of biomolecular interaction analysis to elucidate the regulatory mechanism of the cysteine synthase complex from <i>Arabidopsis thaliana</i>

Real time biomolecular interaction analysis based on surface plasmon resonance has been proven useful for studying protein- protein interaction but has not been extended so far to investigate enzyme-enzyme interactions, especially as pertaining to regulation of metabolic activity. We have applied BIAcore technology to study the regulation of enzyme-enzyme interaction during mitochondrial cysteine biosynthesis in <i>Arabidopsis thaliana</i>. The association of the two enzyme subunits in the hetero-oligomeric cysteine synthase complex was investigated with respect to the reaction intermediate and putative effector O-acetylserine. We have determined an equilibrium dissociation constant of the cysteine synthase complex (<i>K</i>D = 25 ± 4 x 10-9 M), based on a reliable A + B <=> AB model of interaction. Analysis of dissociation kinetics in the presence of O-acetylserine revealed a half-maximal dissociation rate at 77 ± 4 ?M O-acetylserine and strong positive cooperativity for complex dissociation. The equilibrium of interaction was determined using an enzyme activity-based approach and yielded a <i>K</i>m value of 58 ± 7 ?M O-acetylserine. Both effector concentrations are in the range of intracellular O-acetylserine fluctuations and support a functional model that integrates effector-driven cysteine synthase complex dissociation as a regulatory switch for the biosynthetic pathway. The results show that BIAcore technology can be applied to obtain quantitative kinetic data of a hetero-oligomeric protein complex with enzymatic and regulatory functio