A gene for speed? The evolution and function of α‐actinin‐3

The alpha-actinins are an ancient family of actin-binding proteins that play structural and regulatory roles in cytoskeletal organisation and muscle contraction. alpha-actinin-3 is the most-highly specialised of the four mammalian alpha-actinins, with its expression restricted largely to fast glycolytic fibres in skeletal muscle. Intriguingly, a significant proportion ( approximately 18%) of the human population is totally deficient in alpha-actinin-3 due to homozygosity for a premature stop codon polymorphism (R577X) in the ACTN3 gene. Recent work in our laboratory has revealed a strong association between R577X genotype and performance in a variety of athletic endeavours. We are currently exploring the function and evolutionary history of the ACTN3 gene and other alpha-actinin family members. The alpha-actinin family provides a fascinating case study in molecular evolution, illustrating phenomena such as functional redundancy in duplicate genes, the evolution of protein function, and the action of natural selection during recent human evolution.     

D(n)-symmetrical tertiary templates for the design of tubular proteins

Antiparallel helical bundles are found in a wide range of proteins. Often, four-helical bundles form tube-like structures, with binding sites for substrates or cofactors near their centers. For example, a transmembrane four-helical bundle in cytochrome bc(1) binds a pair of porphyrins in an elongated central cavity running down the center of the structure. Antiparallel helical barrels with larger diameters are found in the crystal structures of TolC and DSD, which form antiparallel 12-helical and six-helical bundles, respectively. The backbone geometries of the helical bundles of cytochrome bc(1), TolC, and DSD are well described using a simple D(n)-symmetrical model with only eight adjustable parameters. This parameterization provides an excellent starting point for construction of minimal models of these proteins as well as the de novo design of proteins with novel functions.     

A genome scan in families from Australia and New Zealand confirms the presence of a maternal susceptibility locus for pre-eclampsia, on chromosome 2

Epidemiological studies have shown that genetic factors contribute to the etiology of the common and serious pregnancy-specific disorder pre-eclampsia (PE)/eclampsia (E). Candidate-gene studies have provided evidence (albeit controversial) of linkage to several genes, including angiotensinogen on 1q42-43 and eNOS on 7q36. A recent medium-density genome scan in Icelandic families identified significant linkage to D2S286 (at 94.05 cM) on chromosome 2p12 and suggestive linkage to D2S321 (at 157.5 cM) on chromosome 2q23. In the present article, the authors report the results of a medium-density genome scan in 34 families, representing 121 affected women, from Australia and New Zealand. Multipoint nonparametric linkage analysis, using the GENEHUNTER-PLUS program, showed suggestive evidence of linkage to chromosome 2 (LOD=2.58), at 144.7 cM, between D2S112 and D2S151, and to chromosome 11q23-24, between D11S925 and D11S4151 (LOD=2.02 at 121.3 cM). Given the limited precision of estimates of the map location of disease-predisposing loci for complex traits, the present finding on chromosome 2 is consistent with the finding from the Icelandic study, and it may represent evidence of the same locus segregating in the population from Australia and New Zealand. The authors propose that the PE/E-linked locus on chromosome 2p should be designated the "PREG1" (pre-eclampsia, eclampsia gene 1) locus.     

The lipocalin protein family: structural and sequence overview

Lipocalins are remarkably diverse at the sequence level yet have highly conserved structures. Most lipocalins share three characteristic conserved sequence motifs - the kernel lipocalins - while others are more divergent family members - the outlier lipocalins - typically sharing only one or two. This classification is a useful tool for analysing the family, and within these large sets are smaller groups sharing much higher levels of sequence similarity. The lipocalins are also part of a larger protein superfamily: the calycins, which includes the fatty acid binding proteins, avidins, a group of metalloproteinase inhibitors, and triabin. The superfamily is characterised by a similar structure (a repeated +1 topology beta-barrel) and by the conservation of a remarkable structural signature.     

Immunosensors: Antibody-based biosensors

The challenges in developing practical immunosensors lie in converting (without added reagents) the binding event into an electrical or optical signal, and in creating fully reversible systems capable of monitoring both increases and decreases in analyte concentration. Numerous approaches are under investigation, some of which should lead to commercial products within a couple of years; their strengths and limitations are reviewed.     

Backbone dynamics of a module pair from the ligand-binding domain of the LDL receptor

The ligand-binding domain of the LDL receptor consists of seven contiguous LDL-A modules. The fifth of these ligand-binding modules is absolutely required for recognition of both LDL and beta-VLDL particles. A four-residue linker of variable sequence connects each pair of modules, except for modules four and five, which are connected by a 12-residue linker. To provide a more detailed understanding of the structural relationship in a typical pair of functionally important LDL-A repeats of the LDLR, we investigated the backbone dynamics of repeats five (LR5) and six (LR6) alone and in the context of the covalently connected LR5-6 pair. Our results reveal substantial flexibility in the four-residue linker connecting the two repeats in the LR5-6 pair. The intrinsic dynamic behavior of each repeat is essentially unchanged when the repeats are covalently connected. These observations indicate that the relative orientation of repeats in LR5-6 is not fixed. Modeled in an extended conformation, the linker can separate LR5 and LR6 by up to 15 A, a distance that would allow substantial freedom of motion of each repeat with respect to the other in the pair.     

Nicotine increases sucrose self-administration and seeking in rats

Associations between nicotine in cigarettes and food consumption may alter the incentive value of food such that food cue-reactivity is exaggerated during abstinence from smoking. This effect may contribute to the weight gain associated with cessation of smoking. We examined the effects of nicotine (0.4 mg/kg base subcutaneous) paired (NPD) or unpaired (NUP) with 10% sucrose self-administration (SA; 0.2 ml/delivery, 1 h/day for 10 days) on SA response rate and intake as well as sucrose cue-reactivity following either 1 or 30 days of forced abstinence. Rats were administered the training dose of nicotine prior to a second, consecutive cue-reactivity session. NPD rats responded at over three times the rate for sucrose and earned nearly twice the number of sucrose deliveries as NUP rats or saline controls. Sucrose cue-reactivity was greater after 30 days versus 1 day of forced abstinence for all groups. History of nicotine exposure had no effect on sucrose cue-reactivity. However, the subsequent injection of nicotine increased sucrose cue-reactivity only in the NPD groups. There were no abstinent-dependent effects of nicotine challenge on sucrose cue-reactivity. A study conducted in parallel with water as the reinforcer revealed a less dramatic effect of nicotine on intake. There was no history or abstinence-dependent effects of nicotine on water cue-reactivity. Nicotine increases the reinforcing effects of sucrose and sucrose-paired cues when nicotine is present. An implication of these findings is that relapse to nicotine (cigarettes) could substantially elevate food cue-reactivity.     

SIRT1 is required for AMPK activation and the beneficial effects of resveratrol on mitochondrial function

Resveratrol induces mitochondrial biogenesis and protects against metabolic decline, but whether SIRT1 mediates these benefits is the subject of debate. To circumvent the developmental defects of germline SIRT1 knockouts, we have developed an inducible system that permits whole-body deletion of SIRT1 in adult mice. Mice treated with a moderate dose of resveratrol showed increased mitochondrial biogenesis and function, AMPK activation, and increased NAD(+) levels in skeletal muscle, whereas SIRT1 knockouts displayed none of these benefits. A mouse overexpressing SIRT1 mimicked these effects. A high dose of resveratrol activated AMPK in a SIRT1-independent manner, demonstrating that resveratrol dosage is a critical factor. Importantly, at both doses of resveratrol no improvements in mitochondrial function were observed in animals lacking SIRT1. Together these data indicate that SIRT1 plays an essential role in the ability of moderate doses of resveratrol to stimulate AMPK and improve mitochondrial function both in vitro and in vivo.