In This Issue
BIOPHYSICS
Atomic models via electron cryomicroscopy
Electron cryomicroscopy (cryo-EM), a useful tool for determining three-dimensional structures of proteins, has slowly inched toward atomic resolution. Xing Zhang et al. used cryo-EM to determine the atomic-scale structure of a viral protein shell, the so-called rotavirus double-layer particle that protects the virus' genome. Images of ice-embedded particles were recorded on a modern high-resolution microscope and processed on a computer by using the new image processing methods. The resolution of their resulting structure matched that of a 3.8 Å structure obtained by x-ray crystallography. The authors report that, at this resolution, mostof the amino acid side chains produced recognizable density, and the amino acid chains could be traced. Although the particle's symmetry was key to achieving this resolution, the authors say that similar resolution will also be obtained from structures with lower symmetry as cryo-EM is developed further. They suggest that the technique could be used in areas of structural biology that are less amenable to traditional techniques, such as x-ray crystallography and NMR spectroscopy. — P.D.
Amino acid side chains (blue) in the VP6 rotavirus protein.
“Near-atomic resolution using electron cryomicroscopy and single-particle reconstruction” by Xing Zhang, Ethan Settembre, Chen Xu, Philip R. Dormitzer, Richard Bellamy, Stephen C. Harrison, and Nikolaus Grigorieff (see pages 1867–1872)
MEDICAL SCIENCES
Microneedles enhance drug delivery
Transdermal drug delivery has proven effective in chronic pain management, treatment for angina and congestive heart failure, and hormone replacement therapy. Transdermal patches typically use less medicine while providing a constant dose throughout the day. Often, the patches can replace unpleasant injection-based drug delivery systems, improving patient compliance. The stratum corneum (outer layer of the skin), however, prevents many drugs from entering the bloodstream. Daniel Wermeling et al. developed a microneedle-based system to enhance delivery of naltrexone, a skin-impermeableμ-opioid receptor antagonist used to treat opiate and alcohol dependence. The micrometer-scale microneedles painlessly pierced the patients' stratum corneum, creating pores through which the medication could be delivered efficiently via a standard transdermal patch; naltrexone quickly reached pharmacologically active steady-state plasma levels in the individuals. The oral form of the drug, in contrast, has an 8-fold variation in pharmacological bioavailability. The authors suggest that the research demonstrates the viability of using microneedle pretreatment in humans to enhance the absorption of skin-impermeable drugs. — F.A.
A 50-microneedle patch.
“Microneedles permit transdermal delivery of a skin-impermeant medication to humans” by Daniel P. Wermeling, Stan L. Banks, David A. Hudson, Harvinder S. Gill, Jyoti Gupta, Mark R. Prausnitz, and Audra L. Stinchcomb (see pages 2058–2063)
PHYSIOLOGY
A molecular cause of muscle damage
Prolonged, extreme exercise such as marathon running and distance cycling damages muscles. Andrew Bellinger et al. report that extreme exercise “remodels” the ryanodine receptor channel RyR1, the primary channel for calcium release from the sarcoplasmic reticulum, and makes RyR1 “leaky.” Remodeled RyR1 is saturated with phosphorylation by PKA and S-nitrosylation at cysteines. Both modifications reduce the channel's affinity for calstabin1, which holds RyR1 shut. Prolongedexercise makes RyR1 leaky, the authors find, and they hypothesize that excess calcium may promote muscle damage via the calcium-dependent protease calpain. The authors provide evidence from experiments on mice, which were killed after a 3-week swimming regimen, and human cyclists, who made tissue donations by thigh biopsy. Compared with controls, RyR1 in muscle tissue from postexercise mice and humans showed similar signs of molecular remodeling and leaky tendencies. Wild-type mice dosed with the benzothiapine derivative S107, which increases the specific affinity of calstabin for RyR1, exhibited greater stamina on treadmills than control subjects. The molecular remodeling that occurs after severe exercise likely does not lead to damage in moderate exercise, the authors say. — K.M.
Calcium signals in a muscle cell during contraction.
“Remodeling of ryanodine receptor complex causes ‘leaky’ channels: A molecular mechanism for decreased exercise capacity” by Andrew M. Bellinger, Steven Reiken, Miroslav Dura, Peter W. Murphy, Shi-Xian Deng, Donald W. Landry, David Nieman, Stephan E. Lehnart, Mahendranauth Samaru, Alain LaCampagne, and Andrew R. Marks (see pages 2198–2202)
MEDICAL SCIENCES
Needle-free vaccinations
Worldwide immunization programs must be inexpensive and easy to administer to be effective, particularly in developing countries where trained medical personnel may be in short supply. Delivering vaccines as an aerosol that can be breathed through a mask offers many advantages over the traditional through-the-needle approach. Max Corbett et al. show that the aerosolized poxvirus vectors NYVAC andMVA provide safe, successful immunogenic responses when given to macaque monkeys. The authors inserted vaccines for HIV-1 (clade C) and HPV into radiolabeled NYVAC and MVA poxvirus vectors, respectively, and administered them in 4-min aerosol doses to subject monkeys. The authors suggest that directing the vaccine at mucosal tissues may give a more effective response for mucosal infections such as HIV and HPV. In vivo scintigraphy showed that the vaccines were absorbed primarily in the mucosal tissues of the lungs and respiratory tract of the monkeys, but not in the brain or eyes. Serum samples showed that the immune response from the aerosolized vaccines was equal to that in an injected control group, lasting at least 6 months when followed by a booster. Side effects from the aerosolized vaccinations were minimal, in the worst cases resembling a common cold, with no long-term effects. — C.E.
Pulmonary vaccine deposition in vivo.
“Aerosol immunization with NYVAC and MVA vectored vaccines is safe, simple, and immunogenic” by Max Corbett, Willy M. Bogers, Jonathan L. Heeney, Stefan Gerber, Christian Genin, Arnaud Didierlaurent, Herman Oostermeijer, Rob Dubbes, Gerco Braskamp, Stéphanie Lerondel, Carmen E. Gomez, Mariano Esteban, Ivanella Kondova, Petra Mooij, Sunita Balla-Jhagjhoorsingh, Niels Beenhakker, Gerrit Koopman, Sjoerd van der Burg, Jean-Pierre Kraehenbuhl, and Alain Le Pape (see pages 2046–2051)
