JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org..Recently, there has been a proliferation of measures responding to demands for accountability and transparency. Using the example of media rankings of law schools, this article argues that the methodological concept of reactivity-the idea that people change their behavior in reaction to being evaluated, observed, or measuredoffers a useful lens for disclosing how these measures effect change. A framework is proposed for investigating the consequences, both intended and unintended, of public measures. The article first identifies two mechanisms, self-fulfilling prophecy and commensuration, that induce reactivity and then distinguishes patterns of effects produced by reactivity. This approach demonstrates how these increasingly fateful public measures change expectations and permeate institutions, suggesting why it is important for scholars to investigate the impact of these measures more systematically.

Protein secretion is a common property of pathogenic microbes. Gram-negative bacterial pathogens use at least 6 distinct extracellular protein secretion systems to export proteins through their multilayered cell envelope and in some cases into host cells. Among the most widespread is the newly recognized Type VI secretion system (T6SS) which is composed of 15-20 proteins whose biochemical functions are not well understood. Using crystallographic, biochemical, and bioinformatic analyses, we identified 3 T6SS components, which are homologous to bacteriophage tail proteins. These include the tail tube protein; the membrane-penetrating needle, situated at the distal end of the tube; and another protein associated with the needle and tube. We propose that T6SS is a multicomponent structure whose extracellular part resembles both structurally and functionally a bacteriophage tail, an efficient machine that translocates proteins and DNA across lipid membranes into cells.bacteriophage ͉ membrane ͉ nanomachine ͉ translocation ͉ virulence

Cystic fibrosis transmembrane conductance regulator (CFTR) is an ATP-binding cassette (ABC) transporter that functions as a chloride channel. Nucleotide-binding domain 1 (NBD1), one of two ABC domains in CFTR, also contains sites for the predominant CF-causing mutation and, potentially, for regulatory phosphorylation. We have determined crystal structures for mouse NBD1 in unliganded, ADP-and ATP-bound states, with and without phosphorylation. This NBD1 differs from typical ABC domains in having added regulatory segments, a foreshortened subdomain interconnection, and an unusual nucleotide conformation. Moreover, isolated NBD1 has undetectable ATPase activity and its structure is essentially the same independent of ligand state. Phe508, which is commonly deleted in CF, is exposed at a putative NBD1-transmembrane interface. Our results are consistent with a CFTR mechanism, whereby channel gating occurs through ATP binding in an NBD1-NBD2 nucleotide sandwich that forms upon displacement of NBD1 regulatory segments.

Cystic fibrosis is caused by defects in the cystic fibrosis transmembrane conductance regulator (CFTR), commonly the deletion of residue Phe-508 (⌬F508) in the first nucleotide-binding domain (NBD1), which results in a severe reduction in the population of functional channels at the epithelial cell surface. Previous studies employing incomplete NBD1 domains have attributed this to aberrant folding of ⌬F508 NBD1. We report structural and biophysical studies on complete human NBD1 domains, which fail to demonstrate significant changes of in vitro stability or folding kinetics in the presence or absence of the ⌬F508 mutation. Crystal structures show minimal changes in protein conformation but substantial changes in local surface topography at the site of the mutation, which is located in the region of NBD1 believed to interact with the first membrane spanning domain of CFTR. These results raise the possibility that the primary effect of ⌬F508 is a disruption of proper interdomain interactions at this site in CFTR rather than interference with the folding of NBD1. Interestingly, increases in the stability of NBD1 constructs are observed upon introduction of second-site mutations that suppress the trafficking defect caused by the ⌬F508 mutation, suggesting that these suppressors might function indirectly by improving the folding efficiency of NBD1 in the context of the full-length protein. The human NBD1 structures also solidify the understanding of CFTR regulation by showing that its two protein segments that can be phosphorylated both adopt multiple conformations that modulate access to the ATPase active site and functional interdomain interfaces.Cystic fibrosis causes lung, liver, pancreas, and reproductive tract disorders, typically leading to death prior to middle age from deterioration in pulmonary function (1). CFTR 1 protein is composed of two membrane spanning domains (MSD1 and MSD2), two nucleotide-binding domains (NBD1 and NBD2), and a regulatory region (R). Although it functions as an ATPgated anion channel, CFTR is a member of the ATP-binding cassette (ABC) transporter superfamily (2) based on high sequence similarity between the NBDs and canonical ABC domains. Understanding the exact molecular pathology caused by the ⌬F508 mutation in CFTR is of great importance in the development of drugs to treat cystic fibrosis because of the prevalence of this mutation in the human population. ⌬F508 CFTR fails to mature appropriately in the endoplasmic reticulum and is poorly populated in the epithelial membrane (3-6). It has been proposed that the primary effect of the ⌬F508 mutation is to cause misfolding of NBD1, which leads to aberrant transport and ultimately targeted proteolytic degradation of CFTR (7,8). Channels harboring the deletion show enhanced sensitivity to proteolytic degradation (9) but have at least partial wild-type chloride conductance properties (4, 10). Canonical ABC domain structures are composed of three subdomains, a central F1-type ATP-binding core subdomain, an antiparallel ␤-sheet (ABC␤) s...

Protein arginine methyltransferases (PRMTs) play important roles in several cellular processes, including signaling, gene regulation, and transport of proteins and nucleic acids, to impact growth, differentiation, proliferation, and development. PRMT5 symmetrically di-methylates the two-terminal ω-guanidino nitrogens of arginine residues on substrate proteins. PRMT5 acts as part of a multimeric complex in concert with a variety of partner proteins that regulate its function and specificity. A core component of these complexes is the WD40 protein MEP50/WDR77/p44, which mediates interactions with binding partners and substrates. We have determined the crystal structure of human PRMT5 in complex with MEP50 (methylosome protein 50), bound to an S-adenosylmethionine analog and a peptide substrate derived from histone H4. The structure of the surprising hetero-octameric complex reveals the close interaction between the seven-bladed β-propeller MEP50 and the N-terminal domain of PRMT5, and delineates the structural elements of substrate recognition.epigenetics | protein-protein complex | A9145C P osttranslational methylation of lysine and arginine residues by protein lysine methyltransferases and protein arginine methyltransferases (PRMTs) alters the activity and interactions of substrate proteins, with crucial consequences to diverse cellular functions (1-3). Histone methylation is an epigenetic mark that plays a vital role in normal cell function, and whose dysregulation is associated with several diseases (4).The PRMT family of methyltransferases belongs to the largest class (class I) of S-adenosylmethionine (AdoMet)-dependent methyltransferase enzymes, responsible for the transfer of a methyl group from AdoMet to the arginine side-chains of histones and other proteins. PRMTs are further subdivided into type I, type II, type III, and type IV enzymes based on their patterns of arginine methylation. Eleven human PRMTs have been identified to date (5), and they all methylate the terminal guanidino nitrogen atoms of arginine residues. Type I PRMT enzymes (PRMT1, -2, -3, -4, -6, and -8) generate ω-NG-monomethyl and ω-NG,NG-asymmetric di-methyl arginines, whereas PRMT5 is a type II PRMT that catalyzes the formation of ω-NG-monomethyl and ω-NG,N′G-symmetric di-methyl arginine residues. PRMT7 was initially thought to have type II activity, but recent evidence suggests that it may be a type III enzyme that is only able to monomethylate substrates to form ω-NG-monomethyl arginine (6). A type IV enzyme that catalyses the formation of δ-N-methyl arginine has been identified in yeast (7). All PRMTs share the highly conserved methyltransferase catalytic domain, and several PRMTs contain additional domains that modulate their activity and specificity. PRMT2, PRMT3, and PRMT9 contain SH3, zinc finger, and TRP2 domains, respectively, and PRMT5 contains a largely uncharacterized N-terminal region.In contrast to type I PRMTs, PRMT5 functions as part of various high molecular weight protein complexes that invariably contain the WD-repe...

In selecting a method to produce a recombinant protein, a researcher is faced with a bewildering array of choices as to where to start. To facilitate decision-making, we describe a consensus 'what to try first' strategy based on our collective analysis of the expression and purification of over 10,000 different proteins. This review presents methods that could be applied at the outset of any project, a prioritized list of alternate strategies and a list of pitfalls that trip many new investigators.

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