ENGINEERING
Complex architectural design on the nanoscale
Guowen Meng et al. have devised a technique to create multiply connected and hierarchically branched nanopores inside of anodic aluminum oxide (AAO) templates. Fabricating structures on the nanoscale is a formidable challenge because current methods to controllably synthesize nanotubes limit their complexity. Nanotubes can be formed inside of rationally designed porous templates, such as AAO, but this method has produced only linear and Y-shaped architectures. To create nanotubes of greater complexity, Meng et al. reduced the anodizing voltage used to create AAO templates by a factor of 
, transforming a linear pore into a symmetrically divided Y shape. By sequentially decreasing the voltage by a factor of 
, the authors created up to four generations of Y branches resembling tree-like structures. The number, frequency, and diameter of branches were controlled through the anodizing voltage strength and length of anodization time. The nanopore template was then used to grow nanostructures such as carbon nanotubes and metallic nanowires, which were removed by etching away the AAO. The researchers predict that this method can produce combinations of Y shapes and multiple branches, yielding a wealth of new architectures that could be used to design nanoscale biomaterials and electronic circuits.
Figure 1.
Carbon nanotube architecture.
“Controlled fabrication of hierarchically branched nanopores, nanotubes, and nanowires” by Guowen Meng, Yung Joon Jung, Anyuan Cao, Robert Vajtai, and Pulickel M. Ajayan (see pages 7074-7078)
BIOCHEMISTRY
Revealing PYP reaction intermediates
Hyotcherl Ihee et al. used time-resolved Laue crystallography to visualize the 3D intermediate structures that arise when the p-coumaric acid chromophore of the photoactive yellow protein (PYP) absorbs blue light. PYP from Halorhodospira halophila is one of the most well established systems for studying the molecular basis of biological light absorption. Ihee et al. conducted all the experiments in pump-probe mode, where the PYP crystal was first illuminated with a laser pulse and then probed with a pulse of x-rays. The authors repeated this process and collected data from 47 time points during the photocycle of PYP over a timespan extending from 1 ns to 1 s. Data analysis of these 47 snapshots yielded five distinct intermediate structures. When light strikes PYP, the C2─C3 bond of the chromophore undergoes a trans-to-cis isomerization. Ihee et al. reported that the first three intermediate structures of the PYP photocycle are volume-conserving and preserve the hydrogen-bonding network, straining the chromophore. The latter two structures release this strain and break the hydrogen bonds. This triggers structural changes in the chromophore that are propagated through the PYP protein, causing structural changes in its N terminus, which then mediates a biological signal.
Figure 2.
Photoactive yellow protein.
“Visualizing reaction pathways in photoactive yellow protein from nanoseconds to seconds” by Hyotcherl Ihee, Sudarshan Rajagopal, Vukica Šrajer, Reinhard Pahl, Spencer Anderson, Marius Schmidt, Friedrich Schotte, Philip A. Anfinrud, Michael Wulff, and Keith Moffat (see pages 7145-7150)
ECOLOGY
Species invasions from Europe to North America
Between the 15th and 20th centuries, more vertebrate species were introduced to North America from Europe than vice versa, correlating with historical patterns of human immigration. For a species to become invasive, animals must be introduced to a new region, become established, and spread. To determine the importance of these stages of invasion, Jonathan Jeschke and David Strayer analyzed when native species of fish, birds, and mammals were introduced between North America and Europe. The authors found that the introduction rate from Europe to North America peaked in the late 19th century but continued to rise in the other direction throughout the 20th century. These results match human immigration patterns: Europeans were the major immigrants to North America up to the 19th century, but those numbers decreased after World War I, and increasing numbers of North Americans emigrate to Europe to this day. Although only ≈5% of native vertebrates were introduced in either direction, ≈25% succeeded in becoming established and spreading. Invasion success rates did not differ for either continent, but more new species were introduced to North America. These findings indicate that, once a vertebrate is introduced, it has a high potential to become invasive.
Figure 3.
Vertebrate introductions from Europe to North America, 15th to 20th centuries.
“Invasion success of vertebrates in Europe and North America” by Jonathan M. Jeschke and David L. Strayer (see pages 7198-7202)
GENETICS
HF1 predisposes age-related macular degeneration
Gregory Hageman et al. report that variants of the HF1 gene, a regulator of the immune complement pathway, can either increase the risk of or protect against age-related macular degeneration (AMD). In previous studies, Hageman et al. implicated the complement system as a pathway involved in AMD; many complement components, including HF1 protein, are found in drusen, the hallmark deposits that form in the macula of individuals with AMD. Hageman et al. analyzed the HF1 gene in 900 AMD patients and 400 matched controls for genetic variations and identified eight SNPs that seem to significantly affect predisposition to AMD. The most frequent SNP was present in 50% of AMD patients and only 29% of controls. Homozygotes for this SNP accounted for 24% of AMD cases and only 8% of controls. Most of the SNPs occupy important functional sites within the HF1 protein, possibly altering binding to heparin, C-reactive protein, and C3b, which play roles in inflammation. The authors suggest that these SNPs may modify the behavior of HF1 and hinder its role in immune activities.
Figure 4.
HF1 immunolocalization in eye.
“A common haplotype in the complement regulatory gene factor H (HF1/CFH) predisposes individuals to age-related macular degeneration” by Gregory S. Hageman, Don H. Anderson, Lincoln V. Johnson, Lisa S. Hancox, Andrew J. Taiber, Lisa I. Hardisty, Jill L. Hageman, Heather A. Stockman, James D. Borchardt, Karen M. Gehrs, Richard J. H. Smith, Giuliana Silvestri, Stephen R. Russell, Caroline C. W. Klaver, Irene Barbazetto, Stanley Chang, Lawrence A. Yannuzzi, Gaetano R. Barile, John C. Merriam, R. Theodore Smith, Adam K. Olsh, Julie Bergeron, Jana Zernant, Joanna E. Merriam, Bert Gold, Michael Dean, and Rando Allikmets (see pages 7227-7232)
MICROBIOLOGY, CHEMISTRY
Antitumor peptides from unculturable bacterial symbionts
Eric Schmidt et al. identified and expressed the patellamide biosynthesis pathway from Prochloron didemni, the cyanobacterial symbiont of the sea squirt Lissoclinum patella. Patellamides are cytotoxic, cyclic peptides suspected to have antitumorigenic properties, although their in vivo ecological functions remain unclear. Development of these bioactive compounds into drugs has been hindered by the difficulty of culturing marine invertebrates in the laboratory. Schmidt et al. isolated the cyanobacteria from reef L. patella collected in Palau and assembled the genome of P. didemni. The authors then searched the genome and found the pat gene cluster, which encodes seven genes for patellamide A and C cyclic peptides, as well as motifs that may direct the cyclization of these peptides. The authors were then able to express both patellamide peptides in a heterologous Escherichia coli system. The researchers also proposed activities for several pat genes based on sequence homology to genes from other clusters, including an uncharacterized pathway from the genome sequence of the cyanobacterium Trichodesmium erythraeum.
Figure 5.
Lissoclinum patella.
“Patellamide A and C biosynthesis by a microcin-like pathway in Prochloron didemni, the cyanobacterial symbiont of Lissoclinum patella” by Eric W. Schmidt, James T. Nelson, David A. Rasko, Sebastian Sudek, Jonathan A. Eisen, Margo G. Haygood, and Jacques Ravel (see pages 7315-7320)