Vancomycin derivative with damaged D-Ala-D-Ala binding cleft binds to cross-linked peptidoglycan in the cell wall of Staphylococcus aureus

Des-N-methylleucyl-4-(4-fluorophenyl)benzyl-vancomycin (DFPBV) retains activity against vancomycin-resistant pathogens despite its damaged d-Ala-d-Ala binding cleft. Using solid-state nuclear magnetic resonance (NMR), a DFPBV binding site in the cell walls of whole cells of Staphylococcus aureus has been identified. The cell walls were labeled with d-[1-(13)C]alanine, [1-(13)C]glycine, and l-[epsilon-(15)N]lysine. Internuclear distances from (19)F of the DFPBV to the (13)C and (15)N labels of the cell-wall peptidoglycan were determined by rotational-echo double-resonance (REDOR) NMR. The (13)C{(19)F} and (15)N{(19)F} REDOR spectra show that, in situ, DFPBV binds to the peptidoglycan as a monomer with its vancosamine hydrophobic side chain positioned near a pentaglycyl bridge. This result suggests that the antimicrobial activity of other vancosamine-modified glycopeptides depends upon both d-Ala-d-Ala stem-terminus recognition (primary binding site) and stem-bridge recognition (secondary binding site).     

Coevolution of parasite virulence and host life history

Most models about the evolutionary interactions between a parasite's virulence and its host's life history neglect two potentially important aspects: epidemiological and coevolutionary feedback. We emphasize their importance by presenting models that describe the coevolution of a semelparous host's age at reproduction and a parasite's virulence in different environmental conditions. In particular, we first show that an epidemiological feedback will lead to a nonmonotonic response of the host's age at reproduction as virulence increases. We then show that the coevolutionary pressure on virulence can lead to complex associations between the host's life history and the parasite's virulence, which would not be expected with more traditional models of host or parasite evolution. Thus, for example, a high mortality rate of the host favours avirulent parasites and late reproduction of the host when the environmental conditions allow the host to grow rapidly, but early reproduction and high virulence when growth is slow.     

The prosequence of human lactase-phlorizin hydrolase modulates the folding of the mature enzyme.

The efficient transport of proteins along the secretory pathway requires that the polypeptide adopts a stably folded conformation to egress the endoplasmic reticulum (ER). The transport-competent precursor of the brush border enzyme LPH, pro-LPH, undergoes an intracellular cleavage process in the trans-Golgi network between Arg(734) and Leu(735) to yield LPH beta(initial). The role of the prodomain comprising the N-terminally located 734 amino acids of pro-LPH, LPH alpha, in the folding events of LPH beta(initial) has been analyzed by the individual expression of both forms in COS-1 cells. Following synthesis at 37 degrees C LPH beta(initial) acquires a misfolded and enzymatically inactive conformation that is degraded by trypsin. A temperature shift to 20 degrees C generates a stable, trypsin-resistant, and enzymatically active LPH beta(initial) indicating that the individual expression of LPH beta(initial) results in a temperature-sensitive conformation. This form interacts at non-permissive temperatures sequentially with the ER chaperones immunoglobulin-binding protein and calnexin resulting in an ER retention. The LPH alpha prodomain resides in the ER when individually expressed. It reveals compact structural features that are stabilized by disulfide bridges. LPH alpha and LPH beta(initial) readily interact with each other upon coexpression, and this interaction appears to trigger the formation of a trypsin-resistant, correctly folded, enzymatically active, and transport-competent LPH beta(initial) polypeptide. These data clearly demonstrate that the proregion of pro-LPH is an intramolecular chaperone that is critically essential in facilitating the folding of the intermediate form LPH beta(initial) in the context of the pro-LPH polypeptide.     

Socio-economic aspects of water management along the coast of Kenya

The coast of Kenya has a narrow coastal plain and stretches from Tanzania in the south to Somalia in the north. A number of important rivers drain through it. Population distribution is quite uneven along this coastal zone having developed in clusters linked to artisanal fishing, trade and port activities. The coast's northern districts of Lamu and Tana River are sparsely populated due to a harsh climate and lack of fresh water. The majority of the population is concentrated in Malindi (formerly part of the big Kilifi district), Kilifi, Mombasa, Kwale and Taita-Taveta districts.The paper discusses the challenges arising from fresh water shortage along the coast of Kenya and presents some proposed policy options that may need to be impemented to minimize the scarcity problems. The Kenyan coast receives fresh water from the rivers Tana, Sabaki, Ramisi and Umba. Other important sources of fresh water are Marere springs, Mzima springs, Tiwi boreholes and the lower slopes of Mt. Kilimanjaro. The coast experiences the problem of rapid population growth which leads to land use changes. Since fresh water is scarce, water-borne diseases are rampant and water has become a marketed good. Because of the critical fresh water shortage in the Kenyan coast, water allocation decisions need to be given considerable attention.     

Two novel prevalent polymorphisms in the hormone-sensitive lipase gene have no effect on insulin sensitivity of lipolysis and glucose disposal.

Free fatty acids released during triglyceride lipolysis play an important role in obesity-associated insulin resistance of glucose disposal. Individual sensitivity of lipolysis to the suppressive effect of insulin varies greatly among healthy subjects. It is possible that genetic factors contribute to this variation. Among the many proteins involved in the regulation of lipolysis, hormone-sensitive lipase (HSL) represents a prime candidate for genetic variants contributing to the biological variation of insulin sensitivity of lipolysis. We determined the insulin sensitivity of lipolysis (suppression of isotopically [primed-continuous infusion of d5 glycerol] measured glycerol rate of appearance) and of glucose disposal, using a three-step (n = 20) or standard (n = 53) hyperinsulinemic euglycemic clamp in 73 healthy, unrelated subjects. To assess the possible role of genetic polymorphisms, we directly sequenced the coding region of the HSL gene and the noncoding exon B from these subjects. We identified two silent mutations and three amino acid polymorphisms: Arg262Met (prevalence, 5%), Glu620Asp (prevalence, 31%) and Ser681Ile (prevalence, 22%). The latter two are located in the regulatory domain of HSL but neither had a significant impact on insulin sensitivity of lipolysis or glucose disposal (with and without adjustment for obesity and age as covariates; all P values > 0.20). We conclude that a number of genetic polymorphisms in HSL exist, some of which are highly prevalent. Neither of the polymorphisms we identified in the coding region, however, contributed measurably to the biological variation of insulin sensitivity in our lean, healthy population.     

Uncertain biotic and abiotic interactions in benthic communities

We analyze marine benthic communities at different sites in Skagerrak with the purpose of understanding the role of exogenous and endogenous factors in explaining the species' temporal dynamics. The previous finding that the dynamics of these species communities are mainly driven and synchronized by environmental (temperature) forcing was only weakly supported when analyzing single-species dynamics at five sites where four of the species were present every year. There was no consistent pattern in how the temperature affected the realized per capita growth rate, either across species at a given site, or among sites for a given species. Furthermore, there was no net-interaction from the community on a given species strong enough to give rise to second-order dynamics. However, when implementing a Multi Dimensional Scaling (MDS) analysis and incorporating all sampling sites and species -we found that the different communities clustered in relation to depth, hence, communities at the same depth were more "similar" than communities at different depth. Revealing the underlying interactions shaping these marine benthic communities is a challenge that calls for an array of various and complementary approaches.     

Ultrastructural studies of dorsal ciliated organs in Spionidae (Annelida: Polychaeta)

The distribution and structural components of dorsal ciliated organs (dco) in 15 species of the Spionidae were studied by scanning- and transmission electron microscopy. Based on the distribution patterns of dco, the investigated species are divided into four non-systematic groups: (I) paired anterior dco, (II) paired dco extending posteriorly for several chaetigers, (III) paired anterior dco in combination with unpaired, sexually dimorphic, metameric dco, and (IV) paired anterior dco in combination with paired, metameric dco. Previous ultrastructural studies have only included species possessing organs of groups I and III. In the present investigation the ultrastructure of dco found in Laonice bahusiensis and Spio cf. filicornis (species with dco of groups II and IV) is studied in an attempt to consider their homology. Apart from the metameric dco of group III, similarities of the cellular components of the dco indicate a homology to nuchal organs.     

1-substituted cyclopropenes: Effective Blocking Agents for Ethylene Action in Plants

A series of 1-alkane substituted cyclopropenes has been prepared and tested as ethylene antagonists using banana fruits as an assay system. 1-Methyl-, 1-ethyl-, 1-propyl-, 1-butyl-, 1-pentyl-, 1-hexyl-, 1-heptyl-, 1-octyl-, 1-nonyl-, and 1-decylcyclopropene were all very active compounds. 1-Methylcyclopropene protected bananas from ethylene with a minimum concentration of 0.7 nl.l^–1 after a 24 h exposure. As the carbon chain length was extended the minimum requirement increased some, but starting with 1-butylcyclopropene, the minimum concentration requirement declined and many cyclopropenes were required in lower concentrations than 1-methylcyclopropene. The time of protection at ambient temperature (22–23 °C) was 12 d for 1-methyl-, 1-ethyl-, 1-propyl-, and 1-butylcyclopropene. 1-Pentylcyclopropene protected bananas for 14 d, 1-hexylcyclopropene for 20 d, 1-heptylcyclopropene for 21 d, 1-octylcyclopropene for 25 d, 1-nonylcyclopropene for 35 d, and 1-decylcyclopropene for 36 d.     

Local enrichment with homopolymeric (dA/dT) DNA in genomes of some lower dipterans and Drosophila melanogaster

An investigation into the chromosomal localization of homopolymeric dA/dT was carried out with species of the genera Rhynchosciara, Chironomus, Drosophila and several other taxa. In situ hybridisation probing mitotic and polytene chromosomes with RNA homopolymers was performed, followed by immunological detection of the DNA/RNA hybrid. Use of this method allowed us to assess specific regions of some dipteran genomes, where the signal was generally, but not always, located in heterochromatic regions. Human and Drosophila chromosome regions known to contain dA/dT runs of up to 153 bp were devoid of consistent labelling. The stability of the rA/dT hybrid formed in situ was in agreement with the T(m) for long rA/dT hybrid complexes, suggesting that the method used in this work is able to identify unusually long homopolymeric dA/dT tracts.