M.C. Richter

Computational and Experimental Evidence for the Evolution of a (βα) 8 -Barrel Protein from an Ancestral Quarter-Barrel Stabilised by Disulfide Bonds

The evolution of the prototypical (beta alpha)(8)-barrel protein imidazole glycerol phosphate synthase (HisF) was studied by complementary computational and experimental approaches. The 4-fold symmetry of HisF suggested that its constituting (beta alpha)(2) quarter-barrels have a common evolutionary origin. This conclusion was supported by the computational reconstruction of the HisF sequence of the last common ancestor, which showed that its quarter-barrels were more similar to each other than are those of extant HisF proteins. A comprehensive sequence analysis identified HisF-N1 [corresponding to (beta alpha)(1-2)] as the slowest evolving quarter-barrel. This finding indicated that it is the closest relative of the common (beta alpha)(2) predecessor, which must have been a stable and presumably tetrameric protein. In accordance with this prediction, a recombinantly produced HisF-N1 protein was properly folded and formed a tetramer being stabilised by disulfide bonds. The introduction of a disulfide bond in HisF-C1 [corresponding to (beta alpha)(5-6)] also resulted in the formation of a stable tetramer. The fusion of two identical HisF-N1 quarter-barrels yielded the stable dimeric half-barrel HisF-N1N1. Our findings suggest a two-step evolutionary pathway in which a HisF-N1-like predecessor was duplicated and fused twice to yield HisF. Most likely, the (beta alpha)(2) quarter-barrel and (beta alpha)(4) half-barrel intermediates on this pathway were stabilised by disulfide bonds that became dispensable upon consolidation of the (beta alpha)(8)-barrel.

Resonant photoemission and XMCD on Mn-based systems

Abstract We report results obtained by resonant photoemission (RPE) and X-ray magnetic circular dichroism (XMCD) in absorption with photon energies around the L 2/3 edges of manganese. The samples contain manganese in different environments and details about the dynamics of electronic structure on one side, magnetic structure on the other side are being discussed. We will present studies on the following samples: submonolayers of Mn on Cu(100), Mn in InAs and thin films of the manganese perovskite LSMO.

Electronic structure of organic titanium bis-phthalocyanine on InAs(001)4

We investigated the electronic structure of ultra thin interface of organic titanium bis-phthalocyanine TiPc 2 deposited on InAs(001)(4 x 2)c-(8 x 2) clean surface, by means of high-resolution core-levels and valence band (VB) photoelectron spectroscopies. In4d, As3d, and Cls core levels were measured for different TiPc 2 thicknesses up to 1 monolayer. Surface core level shifts were found on both In4d andAs3d core levels. These shifts originate from the interaction between 4 x 2-c(8 x 2) InAs reconstruction and organic molecules suggesting the presence of strong bounds. C1 core level exhibits a line shape attributed to the C-C and C-N bonds. The VB spectroscopy shows dramatic changes related to the interaction of the TiPc 2 molecule with the InAs related surface states.