Fast dynamics of halophilic malate dehydrogenase and BSA measured by neutron scattering under various solvent conditions influencing protein stability

Protein thermal dynamics was evaluated by neutron scattering for halophilic malate dehydrogenase from Haloarcula marismortui (HmMalDH) and BSA under different solvent conditions. As a measure of thermal stability in each case, loss of secondary structure temperatures were determined by CD. HmMalDH requires molar salt and has different stability behavior in H(2)O, D(2)O, and in NaCl and KCl solvents. BSA remains soluble in molar NaCl. The neutron experiments provided values of mean-squared atomic fluctuations at the 0.1 ns time scale. Effective force constants, characterizing the mean resilience of the protein structure, were calculated from the variation of the mean-squared fluctuation with temperature. For HmMalDH, resilience increased progressively with increasing stability, from molar NaCl in H(2)O, via molar KCl in D(2)O, to molar NaCl in D(2)O. Surprisingly, however, the opposite was observed for BSA; its resilience is higher in H(2)O where it is less stable than in D(2)O. These results confirmed the complexity of dynamics–stability relationships in different proteins. Softer dynamics for BSA in D(2)O showed that the higher thermostability is associated with entropic fluctuations. In the halophilic protein, higher stability is associated with increased resilience showing the dominance of enthalpic terms arising from bonded interactions. From previous data, it is suggested that these are associated with hydrated ion binding stabilizing the protein in the high-salt solvent

Using Conceptual Structures in the Design of Computer-based Assessment Software

Abstract. This paper discusses the use of conceptual structures in the design of computer-based assessment (CBA) tools for e-assessment of programming exercises. In STEM (science, technology, engineering and maths) subjects, universities often observe high dropout and failure rates among the first year students. There are a number of research initiatives that investigate the use of interactive teaching methods and e-learning technologies for improving STEM education. This paper presents a conceptual model of programming exercises and discusses more generally how conceptual structures can be employed for the implementation of CBA tools.