Membrane Interaction of the Glycosyltransferase WaaG

The glycosyltransferase WaaG is involved in the synthesis of lipopolysaccharides that constitute the outer leaflet of the outer membrane in Gram-negative bacteria such as Escherichia coli. WaaG has been identified as a potential antibiotic target, and inhibitor scaffolds have previously been investigated. WaaG is located at the cytosolic side of the inner membrane, where the enzyme catalyzes the transfer of the first outer-core glucose to the inner core of nascent lipopolysaccharides. Here, we characterized the binding of WaaG to membrane models designed to mimic the inner membrane of E. coli. Based on the crystal structure, we identified an exposed and largely α-helical 30-residue sequence, with a net positive charge and several aromatic amino acids, as a putative membrane-interacting region of WaaG (MIR-WaaG). We studied the peptide corresponding to this sequence, along with its bilayer interactions, using circular dichroism, fluorescence quenching, fluorescence anisotropy, and NMR. In the presence of dodecylphosphocholine, MIR-WaaG was observed to adopt a three-dimensional structure remarkably similar to the segment in the crystal structure. We found that the membrane interaction of WaaG is conferred at least in part by MIR-WaaG and that electrostatic interactions play a key role in binding. Moreover, we propose a mechanism of anchoring WaaG to the inner membrane of E. coli, where the central part of MIR-WaaG inserts into one leaflet of the bilayer. In this model, electrostatic interactions as well as surface-exposed Tyr residues bind WaaG to the membrane.     

Vanishing native American dog lineages

Background  

Dogs were an important element in many native American cultures at the time Europeans arrived. Although previous ancient DNA studies revealed the existence of unique native American mitochondrial sequences, these have not been found in modern dogs, mainly purebred, studied so far.     

Lecithin translational diffusion studied by pulsed nuclear magnetic resonance.

The translational diffusion coefficient of egg yolk and dilauroyl lecithin in optically isotropic phases containing sodium cholate has been measured using the pulsed NMR magnetic field gradient method. After a correction for geometrical factors the measured diffusion coefficient is found to agree well with previous determinations in phospholipid systems. The experimental data imply that the cubic mesophase of the lecithin-sodium cholate-water system contains continuous lipid aggregates. A possible model of the arrangement of the different amphiphile molecules in the cubic phase is discussed.     

COMP (cartilage oligomeric matrix protein) is structurally related to the thrombospondins.

Cloning and sequence analysis of cartilage oligomeric matrix protein (COMP) cDNA, representing a cartilage pentameric protein, revealed a protein of 755 amino acid residues with a calculated molecular mass of 82,700 Da. Expression of the cDNA in COS cells showed that COMP is a homopolymer composed of five identical disulfide-linked subunits. COMP is homologous to the carboxyl-terminal half of thrombospondin, and the homologies include 89% and 54% of the residues in COMP and thrombospondin, respectively. The similarities are most pronounced in the carboxyl-terminal domains and in the calcium binding type 3 repeat domains in which about 60% of the amino acid residues are identical. In the type 2/epidermal growth factor repeat domains the two proteins contain 41% identical residues. The sequence of the amino-terminal 84-amino acid residues is unique for COMP. Comparison of the amino acid sequences in the type 2 and type 3 repeat domains of COMP and the thrombospondins shows that COMP is the product of a unique gene and not the result of an alternatively spliced thrombospondin gene.     

A popular misapplication of evolutionary modeling to the study of human cooperation

To examine the evolutionary basis of a behavior, an established approach (known as the phenotypic gambit) is to assume that the behavior is controlled by a single allele, the fitness effects of which are derived from a consideration of how the behavior interacts, via life-history, with other ecological factors. Here we contrast successful applications of this approach with several examples of an influential and superficially similar line of research on the evolutionary basis of human cooperation. A key difference is identified: in the latter line of research the focal behavior, cooperation, is abstractly defined in terms of immediate fitness costs and benefits. Selection is then assumed to act on strategies in an iterated social context for which fitness effects can be derived by aggregation of the abstractly defined immediate fitness effects over a lifetime. This approach creates a closed theoretical loop, rendering models incapable of making predictions or providing insight into the origin of human cooperation. We conclude with a discussion of how evolutionary approaches might be appropriately used in the study of human social behavior.     

A simple prostaglandin bioassay based on smooth muscle preparations from the human oviduct

A simple bioassay for the detection of PGE2, PGF2 alpha and PGI2 was developed by the use of smooth muscle preparations from the human oviduct. The circular muscle layer showed opposite responses to PGE2 and PGF2 alpha while the tubal artery was expedient to distinguish PGE2 from PGI2. As compared to earlier described PG bioassays the system showed a high sensitivity and the limit for detection of an unknown sample was approx. 1 ng. Also combinations of PGs could be identified when reference samples were administered parallel to the unknown samples. It is suggested that the described PG bioassay when further developed may be advantageous for certain purposes since the tissue material generally can be obtained at routine gynecological operations, thus avoiding the use of laboratory animals.