Novel 3-O-carbamoyl erythromycin A derivatives (carbamolides) with activity against resistant staphylococcal and streptococcal isolates

A novel series of 3-O-carbamoyl erythromycin A derived analogs, labeled carbamolides, with activity versus resistant bacterial isolates of staphylococci (including macrolide and oxazolidinone resistant strains) and streptococci are reported. An (R)-2-aryl substituent on a pyrrolidine carbamate appeared to be critical for achieving potency against resistant strains. Crystal structures showed a distinct aromatic interaction between the (R)-2-aryl (3-pyridyl for 4d) substituent on the pyrrolidine and G2484 (G2505, Escherichia coli) of the Deinococcus radiodurans 50S ribosome (3.2 Å resolution).     

Foreword: Protein acylation and microdomains in membrane function

The Signal Recognition Particle (SRP) plays a critical role in the sorting of nascent secretory and membrane proteins. Remarkably, this function has been conserved from bacteria, where SRP delivers proteins to the inner membrane, through to eukaryotes, where SRP is required for targeting of proteins to the endoplasmic reticulum. This review focuses on present understanding of SRP structure and function and the relationship between the two. Furthermore, the similarities and differences in the structure, function and cellular role of SRP in bacteria, chloroplasts, fungi and mammals will be stressed.     

A Homogeneous,High-Throughput Assay for Phosphatidylinositol 5-Phosphate 4-Kinase with a Novel,Rapid Substrate Preparation

Phosphoinositide kinases regulate diverse cellular functions and are important targets for therapeutic development for diseases, such as diabetes and cancer. Preparation of the lipid substrate is crucial for the development of a robust and miniaturizable lipid kinase assay. Enzymatic assays for phosphoinositide kinases often use lipid substrates prepared from lyophilized lipid preparations by sonication, which result in variability in the liposome size from preparation to preparation. Herein, we report a homogeneous 1536-well luciferase-coupled bioluminescence assay for PI5P4Kα. The substrate preparation is novel and allows the rapid production of a DMSO-containing substrate solution without the need for lengthy liposome preparation protocols, thus enabling the scale-up of this traditionally difficult type of assay. The Z’-factor value was greater than 0.7 for the PI5P4Kα assay, indicating its suitability for high-throughput screening applications. Tyrphostin AG-82 had been identified as an inhibitor of PI5P4Kα by assessing the degree of phospho transfer of γ-³²P-ATP to PI5P; its inhibitory activity against PI5P4Kα was confirmed in the present miniaturized assay. From a pilot screen of a library of bioactive compounds, another tyrphostin, I-OMe tyrphostin AG-538 (I-OMe-AG-538), was identified as an ATP-competitive inhibitor of PI5P4Kα with an IC₅₀ of 1 µM, affirming the suitability of the assay for inhibitor discovery campaigns. This homogeneous assay may apply to other lipid kinases and should help in the identification of leads for this class of enzymes by enabling high-throughput screening efforts.     

A phylogeographic study of the stoneplant Conophytum (Aizoaceae; Ruschioideae; Ruschieae) in the Bushmanland Inselberg Region (South Africa) suggests anemochory

The Bushmanland Inselberg Region (BIR) of South Africa provides an ideal system to study population interactions, as these inselbergs function as islands of Succulent Karoo surrounded by Nama Karoo vegetation. The population genetics of four Conophytum taxa endemic to the quartz-associated habitats of inselbergs in the BIR were investigated using amplified fragment length polymorphisms (AFLP), namely C. marginatum subsp. haramoepense, C. marginatum subsp. marginatum, C. maughanii, and C. ratum. Conophytum marginatum colonizes the quartz outcrops on the summits of the inselbergs, while C. maughanii and C. ratum occupy quartz patches at the summit and base of the inselbergs. A total of 24 populations were sampled to assess genetic differentiation between populations of each species, specifically between summit and base populations of C. ratum, eastern and western populations of C. maughanii and populations of the two subspecies of C. marginatum. Moderate levels of genetic differentiation were recovered between the summit and base populations of C. ratum, with an indication of some genetic connectivity between the populations. Slight differentiation between the eastern and western populations of C. maughanii was recovered, however, this was not reflected in the PCoA and STRUCTURE results. In C. marginatum, no significant genetic differentiation was recovered between populations of the subspecies. These results may reflect evidence of different dispersal mechanisms in the species, with the genetic connectivity between populations of C. ratum possibly indicating dispersal through hygrochastic capsules, while genetic connectivity between populations of C. maughanii and C. marginatum may, for the first time, suggest long-distance dispersal, i.e. anemochory. This study provides the first insights into population interactions across the BIR and highlights the importance of conservation in the region, particularly of the Gamsberg, in light of the recent mining activities.     

The 1998 list

A list of names published or validated in 1998 is presented.     

Microfibrillar structure of PGG-glucan in aqueous solution as triple-helix aggregates by small angle x-ray scattering.

The conformation of polysaccharide PGG-Glucan, isolated from yeast cell walls, in aqueous solution was investigated by small angle x-ray scattering (SAXS) and multidetector gel permeation chromatography coupled with postcolumn delivery (GPC/PCD) techniques in comparison with scleroglucan. It was shown that both polysaccharides exhibit a rigid rod-like conformation in aqueous solution by SAXS experiments. The mass per unit length (M/L) and radius (R) of rod cross section of PGG-Glucan were measured to be 6300 daltons/nm and 1.89 nm, while those of scleroglucan are 2300 and 0.83, respectively. Utilizing a GPC/light scattering technique, the average aggregation number of PGG-Glucan is 9, while that of scleroglucan is around 3. From the comparison of the M/L and R of the respective rod cross sections as well as their aggregation number data, it is concluded that PGG-Glucan is composed of triple helices, which tend to aggregate as triplets in solution, whereas scleroglucan is composed of a single triple helix. The aggregation number distribution of PGG-Glucan was found to range from 1 to about 25 determined by GPC/PCD. From the observation of a Debye-Scherrer ring type of peak in the macroscopic scattering cross section of PGG-Glucan by SAXS, the existence of a small amount of ordered clusters of PGG-Glucan can be deduced. The "lattice parameter" of these ordered fasces-like clusters is consistent with the radius of the individual triple-helical rods forming a microfibrillar superstructure. These results indicate that higher aggregated forms of PGG-Glucan containing up to 8 triple helices behave as ordered fasces-like clusters. We conclude that PGG-Glucan is triple-helix aggregates formed by rigid rods stacking together side by side. We propose a molecular structural model for PGG-Glucan conformations.