Integrated Calendar

The primary event of vision in the vertebrate eye is the highly selective and efficient photoisomerization of 11-cis-retinal protonated Schiff base (RPSB) bound to the visual protein rhodopsin (Rh). With a ~100% selectivity, ~65% quantum yield, and ~200 fs product appearance time, this isomerization is considered the archetype of a photochemical reaction optimized by nature to achieve a specific molecular response.
Recently, we have used a combination of a quantum chemical and a classical force field method (QM/MM) to resolve the isomerization mechanism for the RPSB chromophore in Rh[1]. Important stereoelectronic factors were found that determine the outcome of the photoisomerization. The same protocol was also applied to investigate the photochemical mechanism of the newly discovered Anabaena Sensory Rhodopsin[2] and of a biomimetic molecular switch that works in solution[3].
Using the same computational protocol we have also studied the ground state (thermal) isomerization.[4] The results of the simulations explain the molecular mechanism of thermal noise in rod photoreceptors and make a direct link to experimentally found correlations for night vision.
References:
[1] Schapiro I, Ryazantsev M N, Frutos L M, Ferré N, Lindh R, Olivucci M. J. Am. Chem. Soc. (2011), 133, 3354.
[2] Schapiro I, Ruhman S. Biochim Biophys Acta. (2014), 1837, 589.
[3] Léonard J, Schapiro I, Briand J, Fusi S, Paccani R R, Olivucci M, Haacke S. Chem. Eur. J. (2012), 18, 15296.
[4] Gozem S, Schapiro I, Ferré N, Olivucci M. Science (2012), 33, 6099.

In this talk I will describe a simple model for the growth of a bacterial population under the challenge of ribosome-targeting antibiotics. The model is statistical physics-like in that it makes a coarse-grained description of the growth process, reduced to three variables within the bacterial cell - the antibiotic concentration, the concentration of ribosomes bound to antibiotics and the concentration of unbound ribosomes. Furthermore, there is biological input from empirically established physiological constraints which relate the three variables. Remarkably the model can explain several observations concerning antibiotic action and bacterial growth rate. In particular the growth-dependent bacterial susceptibility is controlled by a single, `universal' parameter and the extreme behaviours correspond to the phenomenological classification into bactericidal and bacteriostatic antibiotics. If time allows I will describe how the predictions of the model are backed up by experimental studies.
Reference:
Growth-dependent bacterial susceptibility to ribosome-targeting antibiotics Philip Greulich, Matthew Scott, Martin R. Evans, Rosalind J. Allen Molecular Systems Biology 11:796 (2015)

The half-supersymmetric Wilson loop in N= 4 SYM is arguably the central non-local operatorin the AdS/CFT correspondence. On the field theory side, the vacuum expectation values of Wilson loops in arbitrary representations of SU(N) are captured to all orders in perturbation theory by a Gaussian matrix model. Of prominent interest are the k-symmetric and k-antisymmetric representations, whose gravitational description is given in termsof D3- and D5-branes, respectively, with fluxes in their world volumes. At leading order in N and λ the agreement in both cases is exact. In this talk we explore the structure of the next-to-leading order correction in the matrix model and compare with existing string theory calculations. We also discuss ways to improve the holographic computations to match the sub-leading corrections in the matrix model.