Targeting C-reactive protein for the treatment of cardiovascular disease

Complement-mediated inflammation exacerbates the tissue injury of ischaemic necrosis in heart attacks and strokes, the most common causes of death in developed countries. Large infarct size increases immediate morbidity and mortality and, in survivors of the acute event, larger non-functional scars adversely affect long-term prognosis. There is thus an important unmet medical need for new cardioprotective and neuroprotective treatments. We have previously shown that human C-reactive protein (CRP), the classical acute-phase protein that binds to ligands exposed in damaged tissue and then activates complement, increases myocardial and cerebral infarct size in rats subjected to coronary or cerebral artery ligation, respectively. Rat CRP does not activate rat complement, whereas human CRP activates both rat and human complement. Administration of human CRP to rats is thus an excellent model for the actions of endogenous human CRP. Here we report the design, synthesis and efficacy of 1,6-bis(phosphocholine)-hexane as a specific small-molecule inhibitor of CRP. Five molecules of this palindromic compound are bound by two pentameric CRP molecules, crosslinking and occluding the ligand-binding B-face of CRP and blocking its functions. Administration of 1,6-bis(phosphocholine)-hexane to rats undergoing acute myocardial infarction abrogated the increase in infarct size and cardiac dysfunction produced by injection of human CRP. Therapeutic inhibition of CRP is thus a promising new approach to cardioprotection in acute myocardial infarction, and may also provide neuroprotection in stroke. Potential wider applications include other inflammatory, infective and tissue-damaging conditions characterized by increased CRP production, in which binding of CRP to exposed ligands in damaged cells may lead to complement-mediated exacerbation of tissue injury.     

Haemagglutinin mutations responsible for the binding of H5N1 influenza A viruses to human-type receptors

H5N1 influenza A viruses have spread to numerous countries in Asia, Europe and Africa, infecting not only large numbers of poultry, but also an increasing number of humans, often with lethal effects. Human and avian influenza A viruses differ in their recognition of host cell receptors: the former preferentially recognize receptors with saccharides terminating in sialic acid-alpha2,6-galactose (SAalpha2,6Gal), whereas the latter prefer those ending in SAalpha2,3Gal (refs 3-6). A conversion from SAalpha2,3Gal to SAalpha2,6Gal recognition is thought to be one of the changes that must occur before avian influenza viruses can replicate efficiently in humans and acquire the potential to cause a pandemic. By identifying mutations in the receptor-binding haemagglutinin (HA) molecule that would enable avian H5N1 viruses to recognize human-type host cell receptors, it may be possible to predict (and thus to increase preparedness for) the emergence of pandemic viruses. Here we show that some H5N1 viruses isolated from humans can bind to both human and avian receptors, in contrast to those isolated from chickens and ducks, which recognize the avian receptors exclusively. Mutations at positions 182 and 192 independently convert the HAs of H5N1 viruses known to recognize the avian receptor to ones that recognize the human receptor. Analysis of the crystal structure of the HA from an H5N1 virus used in our genetic experiments shows that the locations of these amino acids in the HA molecule are compatible with an effect on receptor binding. The amino acid changes that we identify might serve as molecular markers for assessing the pandemic potential of H5N1 field isolates.     

Winter forest soil respiration controlled by climate and microbial community composition

Most terrestrial carbon sequestration at mid-latitudes in the Northern Hemisphere occurs in seasonal, montane forest ecosystems. Winter respiratory carbon dioxide losses from these ecosystems are high, and over half of the carbon assimilated by photosynthesis in the summer can be lost the following winter. The amount of winter carbon dioxide loss is potentially susceptible to changes in the depth of the snowpack; a shallower snowpack has less insulation potential, causing colder soil temperatures and potentially lower soil respiration rates. Recent climate analyses have shown widespread declines in the winter snowpack of mountain ecosystems in the western USA and Europe that are coupled to positive temperature anomalies. Here we study the effect of changes in snow cover on soil carbon cycling within the context of natural climate variation. We use a six-year record of net ecosystem carbon dioxide exchange in a subalpine forest to show that years with a reduced winter snowpack are accompanied by significantly lower rates of soil respiration. Furthermore, we show that the cause of the high sensitivity of soil respiration rate to changes in snow depth is a unique soil microbial community that exhibits exponential growth and high rates of substrate utilization at the cold temperatures that exist beneath the snow. Our observations suggest that a warmer climate may change soil carbon sequestration rates in forest ecosystems owing to changes in the depth of the insulating snow cover.     

NIPBL, encoding a homolog of fungal Scc2-type sister chromatid cohesion proteins and fly Nipped-B, is mutated in Cornelia de Lange syndrome

Cornelia de Lange syndrome (CdLS) is a multiple malformation disorder characterized by dysmorphic facial features, mental retardation, growth delay and limb reduction defects. We indentified and characterized a new gene, NIPBL, that is mutated in individuals with CdLS and determined its structure and the structures of mouse, rat and zebrafish homologs. We named its protein product delangin. Vertebrate delangins have substantial homology to orthologs in flies, worms, plants and fungi, including Scc2-type sister chromatid cohesion proteins, and D. melanogaster Nipped-B. We propose that perturbed delangin function may inappropriately activate DLX genes, thereby contributing to the proximodistal limb patterning defects in CdLS. Genome analyses typically identify individual delangin or Nipped-B-like orthologs in diploid animal and plant genomes. The evolution of an ancestral sister chromatid cohesion protein to acquire an additional role in developmental gene regulation suggests that there are parallels between CdLS and Roberts syndrome.     

A synaptic laminin-calcium channel interaction organizes active zones in motor nerve terminals

Synapse formation requires the differentiation of a functional nerve terminal opposite a specialized postsynaptic membrane. Here, we show that laminin beta2, a component of the synaptic cleft at the neuromuscular junction, binds directly to calcium channels that are required for neurotransmitter release from motor nerve terminals. This interaction leads to clustering of channels, which in turn recruit other presynaptic components. Perturbation of this interaction in vivo results in disassembly of neurotransmitter release sites, resembling defects previously observed in an autoimmune neuromuscular disorder, Lambert-Eaton myasthenic syndrome. These results identify an extracellular ligand of the voltage-gated calcium channel as well as a new laminin receptor. They also suggest a model for the development of nerve terminals, and provide clues to the pathogenesis of a synaptic disease.     

Computational roles for dopamine in behavioural control

Neuromodulators such as dopamine have a central role in cognitive disorders. In the past decade, biological findings on dopamine function have been infused with concepts taken from computational theories of reinforcement learning. These more abstract approaches have now been applied to describe the biological algorithms at play in our brains when we form value judgements and make choices. The application of such quantitative models has opened up new fields, ripe for attack by young synthesizers and theoreticians.     

Coupling of agonist binding to channel gating in an ACh-binding protein linked to an ion channel

Neurotransmitter receptors from the Cys-loop superfamily couple the binding of agonist to the opening of an intrinsic ion pore in the final step in rapid synaptic transmission. Although atomic resolution structural data have recently emerged for individual binding and pore domains, how they are linked into a functional unit remains unknown. Here we identify structural requirements for functionally coupling the two domains by combining acetylcholine (ACh)-binding protein, whose structure was determined at atomic resolution, with the pore domain from the serotonin type-3A (5-HT3A) receptor. Only when amino-acid sequences of three loops in ACh-binding protein are changed to their 5-HT3A counterparts does ACh bind with low affinity characteristic of activatable receptors, and trigger opening of the ion pore. Thus functional coupling requires structural compatibility at the interface of the binding and pore domains. Structural modelling reveals a network of interacting loops between binding and pore domains that mediates this allosteric coupling process.