Malaria vaccines--progress and problems.

Developing a vaccine against malaria is a major priority of the WHO. A decade of research exploiting the techniques of molecular biology has yielded a series of potentially protective vaccines. However, progress has been frustrated by the complexity of the parasite's life cycle and the antigenic diversity exhibited by each stage. Although candidate vaccines are now entering human trials, questions still arise concerning the nature of a successful malaria vaccine and who will benefit from it.     

Computer stimulation of sedimentation in the ultracentrifuge. VII. Solutes undergoing indefinite self-association

The velocity sedimentation of solutes involved in self-association equilibria of the indefinite type was simulated using a computer model. The changes in boundary shape that resulted from varying the association constant and the molecular weight of the self-associating monomer were examined. Both ideally and nonideally sedimenting solutes were considered, and several alternative treatments of the variation of the frictional ratio with molecular size were used. All of the calculated boundaries were skewed, with the leading limb of the gradient profile steeper than the trailing limb. For relatively tightly self-associating solutes, the boundaries were very broad and strongly skewed. No shoulders or subsidiary peaks were observed for any of the model solutes used.     

Antiviral agents 2. Synthesis of trimeric naphthoquinone analogues of conocurvone and their antiviral evaluation against HIV

The synthesis of a new series of conocurvone analogues is presented that explores the importance of the pyran rings of conocurvone, their degree of unsaturation as well as the role of alkoxy functionalities as pyran ring replacements, for the inhibition of the HIV-1 integrase (IN) enzyme. Difficulties in synthesising a trimeric naphthoquinone where the central quinone bears a peri-dihydropyran ring was attributed to distortion of the electrophilic dihaloquinone successfully utilised in the past. Increased electron density could also be a factor in reducing reactivity. The desired central dihydropyran bearing trimeric naphthoquinone was successfully synthesised by using a more reactive bromo-tosyloxyquinone intermediate. A maleimide derivative, where the central quinone between the pendant hydroxyquinones was replaced, was successfully synthesised and although it exhibited comparable enzyme inhibitory activity it had negligible HIV inhibitory cellular activity. Compounds were assessed for activity in both in vitro assays using purified recombinant HIV-1 IN and demonstrated superior or comparable activity to conocurvone derivatives previously reported.     

The chloroplast beta-subunit allows assembly of the Escherichia coli F0 portion of the energy transducing adenosine triphosphatase.

The effect of the expression of the chloroplast F1-ATPase beta-subunit in two Escherichia coli beta-subunit mutant strains was investigated. The amount of chloroplast beta-subunit formed in E. coli was increased by introducing a 'Shine-Dalgarno' sequence upstream from the translation start site. The chloroplast beta-subunit was membrane bound but was unable to functionally replace the mutant beta-subunit in a strain carrying the uncD409 allele [corrected]. However, in an E. coli mutant strain unable to form the beta- and epsilon-subunits the presence of the chloroplast beta-subunit enabled the assembly of a functional proton pore [corrected]     

The elimination of the yeast [PSI+] prion by guanidine hydrochloride is the result of Hsp104 inactivation

In the yeast Saccharomyces cerevisiae, Sup35p (eRF3), a subunit of the translation termination complex, can take up a prion-like, self-propagating conformation giving rise to the non-Mendelian [PSI+] determinant. The replication of [PSI+] prion seeds can be readily blocked by growth in the presence of low concentrations of guanidine hydrochloride (GdnHCl), leading to the generation of prion-free [psi-] cells. Here, we provide evidence that GdnHCl blocks seed replication in vivo by inactivation of the molecular chaperone Hsp104. Although growth in the presence of GdnHCl causes a modest increase in HSP104 expression (20-90%), this is not sufficient to explain prion curing. Rather, we show that GdnHCl inhibits two different Hsp104-dependent cellular processes, namely the acquisition of thermotolerance and the refolding of thermally denatured luciferase. The inhibitory effects of GdnHCl protein refolding are partially suppressed by elevating the endogenous cellular levels of Hsp104 using a constitutive promoter. The kinetics of GdnHCl-induced [PSI+] curing could be mimicked by co-expression of an ATPase-negative dominant HSP104 mutant in an otherwise wild-type [PSI+] strain. We suggest that GdnHCl inactivates the ATPase activity of Hsp104, leading to a block in the replication of [PSI+] seeds.