Wednesday 14:00-15:00, Physics Room 5

Jan. 21

Prof. Bernd Rieger, Delft Technical University.

DNA Deformations near Charged Surfaces: Electron and Atomic Force Microscopy Views

DNA is a very important cell structural element, which determines the level of expression of genes by virtue of its interaction with regulatory proteins. We use electron (EM) and atomic force microscopy (AFM) to characterize the flexibility of double-stranded DNA (~150-950 nm long) close to a charged surface. Automated procedures for the extraction of DNA contours (~10-120 nm for EM data and ~10-300 nm for AFM data) combined with new statistical chain descriptors indicate a uniquely twodimensional equilibration of the molecules on the substrate surface regardless of the procedure of molecule mounting. However, in contrast to AFM, the EM mounting leads to a noticeable decrease in DNA persistence length together with decreased kurtosis. Analysis of local bending on short length scales (down to 6 nm in the EM study) shows that DNA flexibility behaves as predicted by the wormlike chain model. We therefore argue that adhesion of DNA to a charged surface may lead to additional static bending (kinking) of ~5 degrees per dinucleotide step without impairing the dynamic behavior of the DNA backbone. Implications of this finding are discussed.
Feb. 03

Prof. Keith Lidke, UNM Physics

I will lead a short discussion on this paper: "Fast, background-free, 3D super-resolution optical fluctuation imaging (SOFI)"
Feb. 10

Prof. Jim Thomas, UNM Physics

Two color FCS and effects of photo-bleaching.
Feb. 17

BPS Meeting student poster pre-presentation.

Feb. 24

BPS Meeting.

March 3

Our seminar is redirected to the BME seminar.

Wednesday, March 3rd, 2010 at 3:00 PM in the Centennial Engineering Center Auditorium (rm 1041 map attached) Michael Kent, Ph. D.
Sandia National Laboratory
Studies of the Structure and Activity of Membrane-Bound HIV Nef Nef is one of six HIV-1 accessory proteins and directly contributes to the progression to AIDS. Nef associates with membranes and may require a transition from a solution conformation to a membrane-associated conformation. It has been hypothesized that a transition from a "closed" conformation to an "open" form enables interaction of Nef with cellular proteins. Despite its medical relevance, there is little or no direct information about the conformation of membrane-bound Nef. In this work we used neutron reflection to reveal the first details of the conformation of membrane-bound Nef. The conformation of Nef was probed for two modes of binding to Langmuir monolayers: interaction of an N-terminal His tag with a synthetic metal-chelating lipid, and through electrostatic interactions with DPPG in the absence of the metal chelating lipid. Several methods were found to achieve a dense monomolecular layer of membrane-bound Nef, despite its tendency to form oligomers at high concentration. The profile of residue density normal to the membrane was quite similar for the two methods of binding. The results show that the core domain of membrane-bound Nef lies within a few of the lipid headgroups, and thus that the Nef protein structure is compact. While the profile of residue density is similar for the two modes of binding, other data indicate stronger insertion of residues into the lipid membrane for binding through the N-terminal His tag. Some ramifications of these results for the activity of Nef will be discussed.
March 10

BPS Re-cap

March 24

Prof. Boris Kiefer, NMSU

Energy -- new solutions for an old problem

Energy production is expected to be one of the most significant challenges in the 21st century. Therefore it is important to develop and explore strategies that reduce the dependence on fossil fuels and provide energy security for future generations. What are the fuels of tomorrow and how can they be converted to useful energy? The global change debate and the pledge by many governments to reduce carbon emissions provide important constraints for fuel evolution and suggests that fuels in particular in the transportation sector will be hydrogen dominated. Fuel cells provide a well suited technology for the conversion of chemical into electrical energy. I will discuss several of my ongoing research projects in surface science and catalysis, that address current challenges in fuel cell applications: sintering/aging/deactivation of catalysts; materials design; and the development of non-Pt catalysts. If time permits I will discuss some possible future research directions.
March 31

Pat Cutler, Fang Huang

Pat will present:

A. Serge, N. Bertaux, H. Rigneault, and D. Marguet. Dynamic multiple-target tracing to probe spatiotemporal cartography of cell membranes. Nature Methods, 5(8):687694. 2008.

and Fang will present:

K. Jaqaman, D. Loerke, M. Mettlen, H. Kuwata, S. Grinstein, S. L. Schmid, and G. Danuser. Robust single-particle tracking in live-cell time-lapse sequences. Nature Methods, 5(8):695702. 2008.