Previous Seminars: 2010

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Date Speaker(s) Organisation Topic
Previous Seminars 2010

9 Dec 2010

John McGeehan

University of Portsmouth

Combining MX and SAXS at the Diamond Light Source:
A finely tuned genetic switch controlling the bacterial immune system

Abstract

Abstract The bacterial restriction-modification (R-M) system serves as an ancient form of innate immunity and provides a basis for the selective destruction of incoming foreign DNA. This system is central to horizontal gene transfer and is a major factor in the transmission of antibiotic resistance between bacterial species. The action of a sequence-specific methylase (M) protects the host DNA from the action of an associated restriction enzyme (R). The expression of the R gene is under the tight control of a small helix-turn-helix controller protein (C) since premature activation of restriction before complete methylation of the host DNA is lethal to the cell. Small molecule intervention of this control mechanism represents a potential target for the design of a novel class of antibiotics. Structural and biophysical techniques have yielded a detailed picture of how this temporal control is achieved at the molecular level. Analysis of the DNA binding and hydrodynamic properties of this transcriptional regulator demonstrates a subtle set of highly cooperative interactions. First, a C-protein dimer binds to the operator sequence and activates transcription by recruiting RNA polymerase. Subsequently, as the C-protein concentration rises rapidly, a second C-protein dimer binds adjacently, displacing RNA polymerase and blocking further expression of both the C and R genes. We now have several high-resolution structures of biologically relevant complexes and from these data we are able to pinpoint the subtleties that result in a concentration dependent on- and off-switch. Recent studies will be presented where beam-lines IO2 and I22 were employed for MX and SAXS experiments, respectively, to study a novel class of controller proteins with unusual structural and binding properties.

5 Nov 2010

Peter Parker

KCL

Signalling Pathways – Mapping, Monitoring and Medicines

14 Oct 2010

Ilan Davis

Oxford University

Using advanced microscopy and image analysis to elucidate the mechanism of mRNA localisation

Abstract
Cytoskeletal organization is central to establishing cell polarity, for example, during microtubule and molecular motor based sorting of mRNA in Drosophila oocytes. However, the dynamics of microtubules and the degree to which the network is polarized remain unclear, as does the molecular basis of microtubule organization. We show that oocyte microtubules are highly dynamic and, using newly developed image analysis tools, as well as novel microscopy approaches such as superresolution by structured illumination. We find a weak global anterior-posterior microtubule polarity bias the strength of which increases gradually towards the posterior. The polarity bias requires Par-1 to suppress microtubule nucleation at the posterior. The microtubule organization we have uncovered explains biased random posterior movements of mRNA and proteins in the oocyte that establish the germ line and body plan. We observed a similar, weak, global microtubule orientation for polarized migratory border cells and propose this mechanism of establishing strong cell polarity is common to oocytes and somatic cells of many animal species.

10 Sept 2010

Guiliano Siligardy

Diamond Light Source

B23 CD beamline: Applications to Life Sciences

Abstract
Circular dichroism (CD) is the spectroscopic technique of choice to characterise chiral molecules such as peptides, proteins, nucleic acids (DNA and RNA), carbohydrates, lipids and small organic molecules (drugs). Although a low resolution technique compared to that of X-ray crystallography and NMR, CD is the technique of choice for systems that do not crystallise or are largely flexible like natively disordered proteins that constitute a significant proportion of proteins. Ligand binding by CD not only provides the stoichiometry and the binding affinity but reveals also whether there are conformational changes induced by the molecular interactions much faster than any other technique.
The combined high photon flux and micro beam make Diamond B23 beamline uniquely suited for CD measurements in micro-devices. Developments in this area together with ligand binding interaction studies of a variety of systems will be discussed.