In This Issue
CHEMISTRY
Stratospheric ice catalyzes chlorine reactions
To explain how ice crystals can catalyze chlorine reactions in the stratosphere, Faye McNeill et al. report that small amounts of hydrochloric acid form a quasiliquid layer on the surface of stratospheric ice crystals. The quasiliquid layer affects the formation of ice in stratospheric clouds and modifies chlorine’s activity in the upper atmosphere and its contributions to ozone depletion, the authors say. McNeill et al. studied how hydrochloric acid alters ice formation in the cold conditions of the stratosphere and found that at pressures as low as 10−6 Torr, hydrochloric acid contributed to the disordering of the liquid surface, which made the chlorine more reactive. The disordered surface only penetrated partially through the ice covering. On the disordered surface, the hydrochloric acid reacted more readily with chlorine nitrate and promoted the adsorption of acetic acid onto the ice crystals. The effects were observed at common stratospheric temperatures and pressures and at temperatures up to 243 K. The authors say that, at temperatures this high, cirrus cloud formation could also be affected. — P.D.
Ice cylinder fragments before and after zone refining.
“Hydrogen chloride-induced surface disordering on ice” by V. Faye McNeill, Thomas Loerting, Franz M. Geiger, Bernhardt L. Trout, and Mario J. Molina (see pages 9422–9427)
CHEMISTRY
Fusing silk and silica
An engineered protein combining the flexibility and tensile strength of spider silk with the resilience of silica has been developed. The result may lead to unique methods of preparing spider silk and producing silica particles with precise sizes to form nanocomposite materials. Cheryl Wong Po Foo et al. developed a fusion protein made of spider silk dragline protein and the silica-cored proteins of diatoms. Taking advantage of silk’s self-assembling properties, the authors made films and fibers from the resulting proteins. The silica particles formed in a narrow range of sizes, spanning 0.5–2 μm, unlike the wider range of sizes formed in the absence of the chimeric protein. The ability to control the size means silica particles with proscribed sizes could be produced in water under ambient conditions. Silica can be difficult to produce in a factory and some routes require high heat input, but diatoms are able to readily produce silica at normal temperatures in aqueous solutions. Wong Po Foo et al. say their technique may allow the production of other resilient minerals, such as hydroxyapatite, and composites involving metals and oxides that are difficult or energy-intensive to fabricate in industrial settings. — P.D.
Genetically engineered silk film.
“Novel nanocomposites from spider silk–silica fusion (chimeric) proteins” by Cheryl Wong Po Foo, Siddharth V. Patwardhan, David J. Belton, Brandon Kitchel, Daphne Anastasiades, Jia Huang, Rajesh R. Naik, Carole C. Perry, and David L. Kaplan (see pages 9428–9433)
BIOCHEMISTRY
Identifying recently synthesized proteins
Several techniques that allow the comparison of cellular protein expression during different states are readily available. However, identifying and separating more recently synthesized proteins from the total pool is troublesome, because all proteins, new and old, share the same pool of amino acids. Daniela Dieterich et al. describe a method, termed bioorthogonal noncanonical amino acid tagging (BONCAT), for enriching newly synthesized proteins. BONCAT entails the incorporation of the azide-bearing amino acid azidohomoalanine as a surrogate for methionine, allowing the protein to be enriched via affinity purification and then identified with tandem mass spectrometry. The authors found that azidohomoalanine addition was nontoxic and did not affect global rates of protein synthesis or degradation. In a sample demonstration, Dieterich et al. successfully identified 195 different proteins, which represented a wide range of biological functions and were unbiased for methionine content, synthesized in cell culture over a 2-h window. This BONCAT technique may allow for a more thorough spatial and temporal analysis of a cell’s response to changing conditions. — N.Z.
First part of BONCAT schematic.
“Selective identification of newly synthesized proteins in mammalian cells using bioorthogonal noncanonical amino acid tagging (BONCAT)” by Daniela C. Dieterich, A. James Link, Johannes Graumann, David A. Tirrell, and Erin M. Schuman (see pages 9482–9487)
EVOLUTION
Sequence of nature’s smallest nucleus
After bacterial endosymbiosis and the first phytoplankton, eukaryotic photosynthesis proliferated rapidly in evolution, as additional eukaryotes absorbed and retained primary plankton, acquiring both nuclear and organelle DNA. The nuclear material eventually disappeared in most cases, but two algae with secondary plastids, the cryptomonads and chlorarachniophytes, provide a rare glimpse into the past by virtue of retaining vestiges of the symbiotic nuclei. Paul Gilson et al. sequenced the complete vestigial nucleus, or nucleomorph, from the chlorarachniophyte Bigelowiella natans. Consisting of three linear chromosomes totaling only 373 kb, 331 genes with minimal upstream or downstream regions, and 852 pygmy introns (18–21 bp each), the B. natans nucleo-morph is the smallest and one of the most compact nuclear genomes known. Only 17 of the 331 genes encode plastid proteins, with the remainder being housekeeping genes. Unlike the case for mitochondria or plastids, Gilson et al. found no mechanistic explanation for permanent retention of a nucleomorph, so it is likely this structure is an evolutionary intermediate waiting to disappear once the essential genes transfer to the host nucleus. — N.Z.
Chlorarachniophytes.
“Complete nucleotide sequence of the chlorarachniophyte nucleomorph: Nature’s smallest nucleus” by Paul R. Gilson, Vanessa Su, Claudio H. Slamovits, Michael E. Reith, Patrick J. Keeling, and Geoffrey I. McFadden (see pages 9566–9571)
GENETICS
Genetic quality of sperm deteriorates with age
The quality of sperm DNA is important for proper genetic development. Andrew Wyrobek et al. report that men can undergo age-related deterioration in the genetic quality of their sperm, suggesting that, as with women, some men who delay reproduction may raise the risk of passing on certain genetic diseases to their children. The authors analyzed mutations in sperm samples of 97 healthy men between the ages of 22 and 80 and found that the frequency of DNA fragmentation and a mutation in a gene that causes achondroplasia (which can cause dwarfism) steadily increased with age, beginning early in reproductive years. No correlation with increasing age was observed for other types of DNA and chromatin damage that could cause sex ratio changes and chromosomal gains or losses that cause diseases like Down’s syndrome. Also, conventional clinical measures of semen quality such as sperm count and motility were found to not be reliable predictors of genomic damage in sperm. The authors say that because some forms of genomic damage increase with age and others do not, overall genomic sperm quality cannot be measured by any single sperm test. — P.D.
“Advancing age has differential effects on DNA damage, chromatin integrity, gene mutations, and aneuploidies in sperm” by A. J. Wyrobek, B. Eskenazi, S. Young, N. Arnheim, I. Tiemann-Boege, E. W. Jabs, R. L. Glaser, F. S. Pearson, and D. Evenson (see pages 9601–9606)
