RNAi tackles polyglutamine disease

Davidson and colleagues have treated a neurodegenerative disease in animals using RNA interference, raising hope that effective therapies can be developed for a group of devastating and currently untreatable genetic disorders. Spinocerebellar ataxia type 1 (SCA1) is caused by an excess of glutamine residues in the ataxin-1 gene. The disease phenotype includes formation of intranuclear aggregates containing the mutant protein, loss of Purkinje cells, thinning of cerebellar molecular layers and progressive ataxia. After identifying short hairpin RNAs that effectively reduce the human ataxin-1 protein in vitro, the authors tested them in SCA1 mice, which express the human disease allele in cerebellar Purkinje cells. The short hairpin RNA was delivered via recombinant adeno-associated virus serotype 1 injected directly into cerebellar lobules. Substantial benefits were seen: aggregates in transduced cells disappeared, molecular layers were restored and motor performance was considerably improved. At least nine progressive brain diseases, including Huntington disease, are linked to expanded polyglutamine tracts and may be amenable to RNAi-based therapies. (Nat. Med. 10, 816–820, 2004) KA

Phage-based rehab

Methadone has proved invaluable for treating heroin addiction, but no similarly effective treatment exists for cocaine addiction. Several small-molecule and antibody drugs have shown limited efficacy, but are hampered by their inability to enter the brain, where cocaine exerts its effects. To overcome this obstacle, Janda and colleagues propose to exploit the recent discovery that bacteriophage displaying a foreign protein can penetrate the brain after intranasal delivery. After immunizing rats over three days with intranasal infusions of phage displaying a murine monoclonal antibody specific to cocaine, the authors gave them daily intraperitoneal injections of low, medium or high doses of cocaine. Although different doses induced different kinds of responses, all the responses were suppressed by phage immunization. No evidence of toxicity was found. The authors suggest that phage-based approaches could be developed for cocaine and other drug addictions. (Proc. Natl. Acad. Sci. USA published online 28 June 2004, doi:10.1073/pnas0403795101) MZ

Proteins arrayed to order

High-density protein arrays have lagged behind DNA arrays because producing large numbers of purified proteins is onerous. Now LaBaer and coworkers describe a technique for producing protein arrays that eliminates the drudgery. Using cell-free transcription/translation systems, they create 'nucleic acid programmable protein arrays.' To create the arrays, they first bind cDNAs to a surface at high density (512 spots/slide) by conjugating psoralen-biotin to the plasmids and applying them to avidin-coated slides. The surface is then overlaid with a reticulocyte lysate and an RNA polymerase, and the translated proteins, engineered to have a glutathione S transferase (GST) tag, are captured on the surface by GST antibody, which also coats the slides. The authors show that they can produce 10 fmoles of proteins per spot, with a variance equivalent to that obtained with conventional protein arrays (sevenfold). Using these arrays to study protein interactions among 29 known replication proteins, they uncovered 63 previously unidentified interactions. (Science 305, 86–90, 2004) LD

Flower power

It's hard to beat photosynthesizers at their own game, but researchers have come close by making electronic devices that incorporate photosynthetic complexes, the biological equivalents of solar energy converters, from spinach and bacteria. Baldo and colleagues have fabricated devices consisting of an organic semiconductor sandwiched between a photosynthetic complex and a metal contact. The authors use Photosystem I, a 14-subunit complex isolated from spinach chloroplasts, and the simpler bacterial photosynthetic reaction center from Rhodobacter sphaeroides, stabilized with peptide surfactants and engineered to contain a molecular tag. The tag allows the complexes to self-assemble in a predetermined orientation on a thin layer of gold evaporated onto a photosensitive glass slide. The spinach complex was incorporated into a photodetector and the bacterial complex contributed converting power to a photovoltaic cell with quantum efficiencies estimated to be approximately 12% and lasting over a period of several weeks. With a bit more tweaking, the efficiency of future devices may exceed 20%, right up there with plants and photosynthetic bacteria. (Nano Lett. 4, 1079–1083, 2004) TM

Arraying energy

The calorimeter has joined the list of laboratory instruments miniaturized in the form of an array. Bruce and colleagues present a calorimetric microarray platform for determining the thermodynamic characteristics (that is, enthalpy, entropy, free energy and even stoichiometry) of a reaction. Changes in enthalpy being a universally measurable characteristic of all molecular interactions, the authors set out to fabricate a nanocalorimetry detector that would be significantly more sensitive than existing microcalorimetry assays as well as amenable for high-throughput applications. The resulting 'enthalpy array' reduces required sample quantities and reaction assay times by nearly three orders of magnitude and can be applied to measuring a variety of interactions, including ligand-binding interactions, enzyme turnover and physiological changes in single organelles. Applications of these arrays range from proteomics and protein chemistry research to high-throughput screening and lead optimization for drug discovery. (Proc. Natl. Acad. Sci. USA 101, 9517–9522, 2004) GTO

Research Highlights written by Kathy Aschheim, Laura DeFrancesco, Teresa Moogan, Gaspar Taroncher-Oldenburg and Mark Zipkin.