Initial cleavage of the human immunodeficiency virus type 1 GagPol precursor by its activated protease occurs by an intramolecular mechanism

Processing of the GagPol polyprotein precursor of human immunodeficiency virus type 1 (HIV-1) is a critical step in viral assembly and replication. The HIV-1 protease (PR) is translated as part of GagPol and is both necessary and sufficient for precursor processing. The PR is active only as a dimer; enzyme activation is initiated when the PR domains in two GagPol precursors dimerize. The precise mechanism by which the PR becomes activated and the subsequent initial steps in precursor processing are not well understood. However, it is clear that processing is initiated by the PR domain that is embedded within the precursor itself. We have examined the earliest events in precursor processing using an in vitro assay in which full-length GagPol is cleaved by its embedded PR. We demonstrate that the embedded, immature PR is as much as 10,000-fold less sensitive to inhibition by an active-site PR inhibitor than is the mature, free enzyme. Further, we find that different concentrations of the active-site inhibitor are required to inhibit the processing of different cleavage sites within GagPol. Finally, our results indicate that the first cleavages carried out by the activated PR within GagPol are intramolecular. Overall, our data support a model of virus assembly in which the first cleavages occur in GagPol upstream of the PR. These intramolecular cleavages produce an extended form of PR that completes the final processing steps accompanying the final stages of particle assembly by an intermolecular mechanism.     

Incorporating mating preferences into a host-parasite model

Mating preferences are incorporated into a host-macroparasite system. Mating preferences of the host and/or parasite can affect the outcome of the host-parasite relationship if certain genotypes of the host are more (or less) affected by the parasite induced death rate than others. Several examples illustrate the situations that can occur.     

ADAR2-dependent RNA editing of AMPA receptor subunit GluR2 determines vulnerability of neurons in forebrain ischemia

ADAR2 is a nuclear enzyme essential for GluR2 pre-mRNA editing at Q/R site-607, which gates Ca2+ entry through AMPA receptor channels. Here, we show that forebrain ischemia in adult rats selectively reduces expression of ADAR2 enzyme and, hence, disrupts RNA Q/R site editing of GluR2 subunit in vulnerable neurons. Recovery of GluR2 Q/R site editing by expression of exogenous ADAR2b gene or a constitutively active CREB, VP16-CREB, which induces expression of endogenous ADAR2, protects vulnerable neurons in the rat hippocampus from forebrain ischemic insult. Generation of a stable ADAR2 gene silencing by delivering small interfering RNA (siRNA) inhibits GluR2 Q/R site editing, leading to degeneration of ischemia-insensitive neurons. Direct introduction of the Q/R site edited GluR2 gene, GluR2(R607), rescues ADAR2 degeneration. Thus, ADAR2-dependent GluR2 Q/R site editing determines vulnerability of neurons in the rat hippocampus to forebrain ischemia.     

Females Remate for Sperm Replenishment in a Seed Bug: Evidence from Offspring Viability

Females of many insects mate multiply but why they do so remains controversial. Here we investigated the effects of multiple matings on female reproductive success of a New Zealand seed bug, Nysius huttoni. We found little evidence for females to gain material (nutritional) benefits through multiple matings because the number of matings did not have significant effect on female fecundity. Females remated to the same males or different males produced similar number of viable offspring, suggesting that females do not obtain genetic benefit from remating in terms of offspring viability. With the increase of the number of matings, however, overall fertility rate significantly increased and daily fertility rate declined significantly slower over time. These results suggest that females remate for the replenishment of sperm. Five matings are sufficient for females to maximize their reproductive success, and additional matings appear to be superfluous. However, the females of this bug mate as many as 68 times if males and females are paired for lifetime. This can be explained by the convenience hypothesis, i.e., females remate superfluously to minimize the costs of harassment by promiscuous males.     

Soluble interleukin-2 receptor as a marker for progression of coronary artery calcification in type 1 diabetes

INTRODUCTION: Soluble interleukin-2 receptor (sIL2r), a marker of T cell activation, is elevated in inflammatory processes, such as rheumatoid arthritis, hepatitis and neoplasm. We explored a potential association between plasma sIL2r levels and progression of coronary artery calcification (CAC), a marker for subclinical atherosclerosis, in a prospectively followed cohort of type 1 diabetic and non-diabetic subjects, aged 20-59 years, with no history of coronary artery disease. MATERIALS AND METHODS: CAC progression was assessed by electron beam tomography over 2.6 years (range 1.6-3.2). Plasma sIL2r levels were measured in a nested case-control substudy of 98 subjects (67 diabetic, 31 non-diabetic) with and 173 subjects (84 diabetic, 89 non-diabetic) without significant CAC progression. Log-transformed sIL2r levels were analyzed by conditional logistic regression to compare subjects with and without significant CAC progression. RESULTS: SIL2r was a significant predictor for CAC progression after adjusting for presence of baseline CAC, age, gender, diabetes status, baseline calcium volume score and adiponectin (OR 1.99, 95% CI 1.09-3.61, p = 0.02 for a doubling of sIL2r level). Addition of BMI, LDL, HDL, hypertension, smoking status, HbA1c, CRP, fibrinogen, homocysteine and PAI-1 to regression models weakened but did not remove sIL2r as a predictor of CAC progression. There was no indication that this effect was different by diabetes status (p = 0.6 for diabetes-sIL2r interaction). DISCUSSION: Elevated plasma sIL2r is associated with CAC progression independent of traditional coronary artery disease risk factors in type 1 diabetic and non-diabetic young adults. SIL2r should be considered as a novel marker of inflammation leading to coronary artery disease.     

E unum pluribus: multiple proteins from a self-processing polyprotein

Many applications of genetic engineering require transformation with multiple (trans)genes, although to achieve these using conventional techniques can be challenging. The 2A oligopeptide is emerging as a highly effective new tool for the facile co-expression of multiple proteins in a single transformation step, whereby a gene encoding multiple proteins, linked by 2A sequences, is transcribed from a single promoter. The polyprotein self-processes co-translationally such that each constituent protein is generated as a discrete translation product. 2A functions in all the eukaryotic systems tested to date and has already been applied, with great success, to a broad range of biotechnological applications: from plant metabolome engineering to the expression of T-cell receptor complexes, monoclonal antibodies or heterodimeric cytokines in animals.     

Malvone A, a phytoalexin found in Malva sylvestris (family Malvaceae)

The isolation and structure of a phytoalexin, malvone A (2-methyl-3-methoxy-5,6-dihydroxy-1,4-naphthoquinone) is reported. Malvone A formation is induced in Malva sylvestris L. by the plant pathogen Verticillium dahliae. In a turbimetric assay for toxicity to V. dahliae, it had an ED50 value of 24 microg/ml. The structure of malvone A was determined by MS and NMR spectroscopy, and by X-ray crystallographic analysis. The X-ray analysis showed water molecules were located in channels that run along the a-axis.