The Origin, Early Evolution and Predictability of Solar Eruptions

Coronal mass ejections (CMEs) were discovered in the early 1970s when space-borne coronagraphs revealed that eruptions of plasma are ejected from the Sun. Today, it is known that the Sun produces eruptive flares, filament eruptions, coronal mass ejections and failed eruptions; all thought to be due to a release of energy stored in the coronal magnetic field during its drastic reconfiguration. This review discusses the observations and physical mechanisms behind this eruptive activity, with a view to making an assessment of the current capability of forecasting these events for space weather risk and impact mitigation. Whilst a wealth of observations exist, and detailed models have been developed, there still exists a need to draw these approaches together. In particular more realistic models are encouraged in order to asses the full range of complexity of the solar atmosphere and the criteria for which an eruption is formed. From the observational side, a more detailed understanding of the role of photospheric flows and reconnection is needed in order to identify the evolutionary path that ultimately means a magnetic structure will erupt

Conserved main-chain peptide distortions: A proposed role for Ile203 in catalysis by dihydrodipicolinate synthase

In recent years, dihydrodipicolinate synthase (DHDPS, E.C. 4.2.1.52) has received considerable attention from a mechanistic and structural viewpoint. DHDPS catalyzes the reaction of (S)-aspartate-β-semialdehyde with pyruvate, which is bound via a Schiff base to a conserved active-site lysine (Lys161 in the enzyme from Escherichia coli). To probe the mechanism of DHDPS, we have studied the inhibition of E. coli DHDPS by the substrate analog, β-hydroxypyruvate. The K i was determined to be 0.21 (±0.02) mM, similar to that of the allosteric inhibitor, (S)-lysine, and β-hydroxypyruvate was observed to cause time-dependent inhibition. The inhibitory reaction with β-hydroxypyruvate could be qualitatively followed by mass spectrometry, which showed initial noncovalent adduct formation, followed by the slow formation of the covalent adduct. It is unclear whether β-hydroxypyruvate plays a role in regulating the biosynthesis of meso-diaminopimelate and (S)-lysine in E. coli, although we note that it is present in vivo. The crystal structure of DHDPS complexed with β-hydroxypyruvate was solved. The active site clearly showed the presence of the inhibitor covalently bound to the Lys161. Interestingly, the hydroxyl group of β-hydroxypyruvate was hydrogen-bonded to the main-chain carbonyl of Ile203. This provides insight into the possible catalytic role played by this peptide unit, which has a highly strained torsion angle (ω ∼201°). A survey of the known DHDPS structures from other organisms shows this distortion to be a highly conserved feature of the DHDPS active site, and we propose that this peptide unit plays a critical role in catalysis