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nature Sept 22
No.1
Structures of complement component C3 provide insights into the function and evolution of immunity
Bert J. C. Janssen1, Eric G. Huizinga1, Hans C. A. Raaijmakers1, Anja Roos2, Mohamed R. Daha2, Kristina Nilsson-Ekdahl3,4, Bo Nilsson3 and Piet Gros1
The mammalian complement system is a phylogenetically ancient cascade system that has a major role in innate and adaptive immunity. Activation of component C3 (1,641 residues) is central to the three complement pathways and results in inflammation and elimination of self and non-self targets. Here we present crystal structures of native C3 and its final major proteolytic fragment C3c. The structures reveal thirteen domains, nine of which were unpredicted, and suggest that the proteins of the 2-macroglobulin family evolved from a core of eight homologous domains. A double mechanism prevents hydrolysis of the thioester group, essential for covalent attachment of activated C3 to target surfaces. Marked conformational changes in the -chain, including movement of a critical interaction site through a ring formed by the domains of the -chain, indicate an unprecedented, conformation-dependent mechanism of activation, regulation and biological function of C3.
No.2
Evolutionary information for specifying a protein fold
Michael Socolich1,2,5, Steve W. Lockless1,2,4,5, William P. Russ1,2, Heather Lee1,2, Kevin H. Gardner2,3 and Rama Ranganathan1,2
Classical studies show that for many proteins, the information required for specifying the tertiary structure is contained in the amino acid sequence. Here, we attempt to define the sequence rules for specifying a protein fold by computationally creating artificial protein sequences using only statistical information encoded in a multiple sequence alignment and no tertiary structure information. Experimental testing of libraries of artificial WW domain sequences shows that a simple statistical energy function capturing coevolution between amino acid residues is necessary and sufficient to specify sequences that fold into native structures. The artificial proteins show thermodynamic stabilities similar to natural WW domains, and structure determination of one artificial protein shows excellent agreement with the WW fold at atomic resolution. The relative simplicity of the information used for creating sequences suggests a marked reduction to the potential complexity of the protein-folding problem.
No.3
Isolation of an autotrophic ammonia-oxidizing marine archaeon
Martin Könneke1,4,3, Anne E. Bernhard1,4,3, José R. de la Torre1,4, Christopher B. Walker1, John B. Waterbury2 and David A. Stahl1
For years, microbiologists characterized the Archaea as obligate extremophiles that thrive in environments too harsh for other organisms. The limited physiological diversity among cultivated Archaea suggested that these organisms were metabolically constrained to a few environmental niches. For instance, all Crenarchaeota that are currently cultivated are sulphur-metabolizing thermophiles1. However, landmark studies using cultivation-independent methods uncovered vast numbers of Crenarchaeota in cold oxic ocean waters2, 3. Subsequent molecular surveys demonstrated the ubiquity of these low-temperature Crenarchaeota in aquatic and terrestrial environments4. The numerical dominance of marine Crenarchaeota—estimated at 1028 cells in the world's oceans5—suggests that they have a major role in global biogeochemical cycles. Indeed, isotopic analyses of marine crenarchaeal lipids suggest that these planktonic Archaea fix inorganic carbon6. Here we report the isolation of a marine crenarchaeote that grows chemolithoautotrophically by aerobically oxidizing ammonia to nitrite—the first observation of nitrification in the Archaea. The autotrophic metabolism of this isolate, and its close phylogenetic relationship to environmental marine crenarchaeal sequences, suggests that nitrifying marine Crenarchaeota may be important to global carbon and nitrogen cycles No.4
Endangered plants persist under phosphorus limitation
Martin J. Wassen1,6, Harry Olde Venterink2,6, Elena D. Lapshina3,5 and Franziska Tanneberger4
Nitrogen enrichment is widely thought to be responsible for the loss of plant species from temperate terrestrial ecosystems. This view is based on field surveys and controlled experiments showing that species richness correlates negatively with high productivity1, 2 and nitrogen enrichment3. However, as the type of nutrient limitation has never been examined on a large geographical scale the causality of these relationships is uncertain. We investigated species richness in herbaceous terrestrial ecosystems, sampled along a transect through temperate Eurasia that represented a gradient of declining levels of atmospheric nitrogen deposition—from 50 kg ha-1 yr-1 in western Europe to natural background values of less than 5 kg ha-1 yr-1 in Siberia4. Here we show that many more endangered plant species persist under phosphorus-limited than under nitrogen-limited conditions, and we conclude that enhanced phosphorus is more likely to be the cause of species loss than nitrogen enrichment. Our results highlight the need for a better understanding of the mechanisms of phosphorus enrichment, and for a stronger focus on conservation management to reduce phosphorus availability.
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作者:admin@医学,生命科学 2011-03-13 05:11
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