Immune recognition. A new receptor for beta-glucans.

The carbohydrate polymers known as beta-1,3-d-glucans exert potent effects on the immune system - stimulating antitumour and antimicrobial activity, for example - by binding to receptors on macrophages and other white blood cells and activating them. Although beta-glucans are known to bind to receptors, such as complement receptor 3 (ref. 1), there is evidence that another beta-glucan receptor is present on macrophages. Here we identify this unknown receptor as dectin-1 (ref. 2), a finding that provides new insights into the innate immune recognition of beta-glucans.     

Evolutionary genetics. Clonal inheritance of avian mitochondrial DNA.

We have taken a new approach to test the commonly accepted, but recently questioned, principle of clonal inheritance of vertebrate mitochondrial DNA (mtDNA) by relating its inheritance to a female-specific marker of nuclear DNA. Whereas this is impossible in organisms with male heterogamy (such as mammals), we show here that genealogies of mtDNA and the female-specific W chromosome of a bird species are completely concordant. Our results indicate that inheritance of mtDNA is free of detectable recombination effects over an evolutionary timescale.     

How 'spin ice' freezes.

The large degeneracy of states resulting from the geometrical frustration of competing interactions is an essential ingredient of important problems in fields as diverse as magnetism, protein folding and neural networks. As first explained by Pauling, geometrical frustration of proton positions is also responsible for the unusual low-temperature thermodynamics of ice and its measured 'ground state' entropy. Recent work has shown that the geometrical frustration of ice is mimicked by Dy2Ti2O7, a site-ordered magnetic material in which the spins reside on a lattice of corner-sharing tetrahedra where they form an unusual magnetic ground state known as 'spin ice'. Here we identify a cooperative spin-freezing transition leading to the spin-ice ground state in Dy2Ti2O7. This transition is associated with a very narrow range of relaxation times, and represents a new form of spin-freezing. The dynamics are analogous to those associated with the freezing of protons in ice, and they provide a means through which to study glass-like behaviour and the consequences of frustration in the limit of low disorder.     

Crystal structure of the β2 adrenergic receptor-Gs protein complex

G protein-coupled receptors (GPCRs) are responsible for the majority of cellular responses to hormones and neurotransmitters as well as the senses of sight, olfaction and taste. The paradigm of GPCR signalling is the activation of a heterotrimeric GTP binding protein (G protein) by an agonist-occupied receptor. The β(2) adrenergic receptor (β(2)AR) activation of Gs, the stimulatory G protein for adenylyl cyclase, has long been a model system for GPCR signalling. Here we present the crystal structure of the active state ternary complex composed of agonist-occupied monomeric β(2)AR and nucleotide-free Gs heterotrimer. The principal interactions between the β(2)AR and Gs involve the amino- and carboxy-terminal α-helices of Gs, with conformational changes propagating to the nucleotide-binding pocket. The largest conformational changes in the β(2)AR include a 14 ? outward movement at the cytoplasmic end of transmembrane segment 6 (TM6) and an α-helical extension of the cytoplasmic end of TM5. The most surprising observation is a major displacement of the α-helical domain of Gαs relative to the Ras-like GTPase domain. This crystal structure represents the first high-resolution view of transmembrane signalling by a GPCR.     

The current structural and functional understanding of APOBEC deaminases

The apolipoprotein B mRNA-editing enzyme catalytic polypeptide (APOBEC) family of cytidine deaminases has emerged as an intensively studied field as a result of their important biological functions. These enzymes are involved in lipid metabolism, antibody diversification, and the inhibition of retrotransposons, retroviruses, and some DNA viruses. The APOBEC proteins function in these roles by deaminating single-stranded (ss) DNA or RNA. There are two high-resolution crystal structures available for the APOBEC family, Apo2 and the C-terminal catalytic domain (CD2) of Apo3G or Apo3G-CD2 [Holden et al. (Nature 456:121–124, 2008); Prochnow et al. (Nature 445:447–451, 2007)]. Additionally, the structure of Apo3G-CD2 has also been determined using NMR [Chen et al. (Nature 452:116–119, 2008); Furukawa et al. (EMBO J 28:440–451, 2009); Harjes et al. (J Mol Biol, 2009)]. A detailed structural analysis of the APOBEC proteins and a comparison to other zinc-coordinating deaminases can facilitate our understanding of how APOBEC proteins bind nucleic acids, recognize substrates, and form oligomers. Here, we review the recent development of structural and functional studies that apply to Apo3G as well as the APOBEC deaminase family.