The reductive electron transfer (ET) in DNA can be studied by ultrafast time-resolved measurements combined with chemically probed DNAstrand-cleavage experiments. Owing to the numerous conformations of DNA present the results show a variety of ET rates. For more information see the Communication by H.-A. Wagenknecht, T. Fiebig, et al. on the following pages.
The molecular origin of the selectivity of N-donor ligands, such as alkylated bis-triazinyl pyridines (BTPs), for actinide complexation in the presence of lanthanides is still largely unclear. NMR investigations of an Am(nPrBTP)3(3+) complex with a (15)N labelled ligand showed that it exhibits large differences in (15)N chemical shift for coordinating N-atoms in comparison to both lanthanide(III) complexes and the free ligand. The temperature dependence of NMR chemical shifts observed for this complex indicates a weak paramagnetism. This fact and the observed large chemical shift for bound nitrogen atoms allow us to conclude that metal-ligand bonding in the reported Am(III) N-donor complex has a larger share of covalence than in lanthanide complexes. This may account for the observed selectivity.
NMR investigations of Am(C5-BPP)33+ show weak paramagnetism in Am(iii), indicating significant covalence in metal–ligand bonds with N-donor ligands. This may explain the observed extraction selectivity for actinides over lanthanides.
Lgt1 is one of the glucosyltransferases produced by the Gramnegative bacterium Legionella pneumophila. This enzyme modifies eukaryotic elongation factor 1A (eEF1A) at serine 53, which leads to inhibition of protein synthesis and death of target cells. Here we studied the region of eEF1A, which is essential for substrate recognition by Lgt1. We report that the decapeptide 50 GKGSFKYAWV 59 of eEF1A is efficiently modified by Lgt1. This peptide covers the loop of the helix-loop-helix region formed by helices A* and A of eEF1A and is part of the first turn of helix A. Substitution of either serine 53, phenylalanine 54, tyrosine 56, or tryptophan 58 by alanine abolished or severely decreased glucosylation. Lgt1 modified the decapeptide 50 GKGSFKYAWV 59 with a higher glucosylation rate than fulllength eEF1A purified from yeast, suggesting that a specific conformation of eEF1A is the preferred substrate of Lgt1. A GenBank TM search on the basis of the substrate decapeptide for similar peptide sequences retrieved heat shock protein 70 subfamily B suppressor 1 (Hbs1) as a target for glucosylation by Lgt1. Recombinant Hbs1 and the corresponding fragment ( 303 GKASFAYAWV 312 ) were glucosylated by Lgt1. NMR studies with the glucosylated eEF1A-derived decapeptide identified an ␣-anomeric structure of the glucose-serine 53 bond and characterize Lgt1 as a retaining glucosyltransferase.Legionella pneumophila is a Gram-negative bacterium, causing pulmonary infectious disease in humans. This microorganism is able to infect various free-living protozoa in natural environment as well as macrophages, monocytes, and lung epithelial cells during human disease (1, 2). A plethora of virulence factors, which are important for intracellular proliferation of the bacteria in target eukaryotic cells, and a type IVB secretion system for intracytoplasmic delivery of these effectors have been identified (3). Among the best studied Legionella products are RalF (4) and DrrA (5), which act as exchange factors for Arf1 and Rab1 small GTPases, respectively. Additionally, DrrA has been shown to possess activity of a guanine nucleotide dissociation inhibitor-displacement factor (6). These two proteins were suggested to participate in recruitment of endosomal vesicles and construction of a replicative phagosome, which is a characteristic intracellular niche of Legionella and prerequisite for subsequent proliferation of the bacteria in host cells (7). However, despite considerable progress, many aspects of intracellular biology of L. pneumophila, in particular those apart from processes associated with alterations in vesicular trafficking, remain poorly understood.In our previous investigations we identified three proteins in L. pneumophila (Lgt1, Lgt2, and Lgt3), which possess enzymatic activity and modify eukaryotic elongation factor eEF1A 3 at serine 53 by mono-O-glucosylation (8 -10). This modification inhibits protein synthesis and is eventually lethal to target cells. Expression of Lgt1 is strongly increased during late phase of bacterial growth ...
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