Structure of lipoprotein lipase in complex with GPIHBP1.

Lipoprotein lipase (LPL) plays a central role in triglyceride (TG) metabolism. By catalyzing the hydrolysis of TGs present in TG-rich lipoproteins (TRLs), LPL facilitates TG utilization and regulates circulating TG and TRL concentrations. Until very recently, structural information for LPL was limited to homology models, presumably due to the propensity of LPL to unfold and aggregate. By coexpressing LPL with a soluble variant of its accessory protein glycosylphosphatidylinositol-anchored high-density lipoprotein binding protein 1 (GPIHBP1) and with its chaperone protein lipase maturation factor 1 (LMF1), we obtained a stable and homogenous LPL/GPIHBP1 complex that was suitable for structure determination. We report here X-ray crystal structures of human LPL in complex with human GPIHBP1 at 2.5-3.0 Å resolution, including a structure with a novel inhibitor bound to LPL. Binding of the inhibitor resulted in ordering of the LPL lid and lipid-binding regions and thus enabled determination of the first crystal structure of LPL that includes these important regions of the protein. It was assumed for many years that LPL was only active as a homodimer. The structures and additional biochemical data reported here are consistent with a new report that LPL, in complex with GPIHBP1, can be active as a monomeric 1:1 complex. The crystal structures illuminate the structural basis for LPL-mediated TRL lipolysis as well as LPL stabilization and transport by GPIHBP1.

A lipoprotein lipase-GPI-anchored high-density lipoprotein-binding protein 1 fusion lowers triglycerides in mice: Implications for managing familial chylomicronemia syndrome.

Lipoprotein lipase (LPL) is central to triglyceride metabolism. Severely compromised LPL activity causes familial chylomicronemia syndrome (FCS), which is associated with very high plasma triglyceride levels and increased risk of life-threatening pancreatitis. Currently, no approved pharmacological intervention can acutely lower plasma triglycerides in FCS. Low yield, high aggregation, and poor stability of recombinant LPL have thus far prevented development of enzyme replacement therapy. Recently, we showed that LPL monomers form 1:1 complexes with the LPL transporter glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein 1 (GPIHBP1) and solved the structure of the complex. In the present work, we further characterized the monomeric LPL/GPIHBP1 complex and its derivative, the LPL-GPIHBP1 fusion protein, with the goal of contributing to the development of an LPL enzyme replacement therapy. Fusion of LPL to GPIHBP1 increased yields of recombinant LPL, prevented LPL aggregation, stabilized LPL against spontaneous inactivation, and made it resistant to inactivation by the LPL antagonists angiopoietin-like protein 3 (ANGPTL3) or ANGPTL4. The high stability of the fusion protein enabled us to identify LPL amino acids that interact with ANGPTL4. Additionally, the LPL-GPIHBP1 fusion protein exhibited high enzyme activity in in vitro assays. Importantly, both intravenous and subcutaneous administrations of the fusion protein lowered triglycerides in several mouse strains without causing adverse effects. These results indicate that the LPL-GPIHBP1 fusion protein has potential for use as a therapeutic for managing FCS.

MRI of the shoulder in adults.

MRI can be used to assist in distinguishing pathology and anatomic disruptions adjacent to shoulder articulations and is a crucial tool in evaluating the symptomatic shoulder. The differentiation of traumatic and degenerative etiologies is important for patient management. A review of common adult degenerative and posttraumatic conditions can help familiarize general orthopaedic surgeons and sports medicine care providers to the perspective of shoulder specialists and musculoskeletal radiologists.

Characterization of recombinant human acetyl-CoA carboxylase-2 steady-state kinetics.

Acetyl-CoA carboxylase (ACC) catalyzes the carboxylation of acetyl-CoA to form malonyl-CoA, a key metabolite in the fatty acid synthetic and oxidation pathways. The present study describes the steady-state kinetic analysis of a purified recombinant human form of the enzyme, namely ACC2, using a novel LC/MS/MS assay to directly measure malonyl-CoA formation. Four dimensional matrices, in which bicarbonate (HCO(3)(-)), ATP, acetyl-CoA, and citrate were varied, and global data fitting to appropriate steady-state equations were used to generate kinetic constants. Product inhibition studies support the notion that the enzyme proceeds through a hybrid (two-site) random Ter Ter mechanism, one that likely involves a two-step reaction at the biotin carboxylase domain. Citrate, a known activator of animal forms of ACC, activates both by increasing k(cat) and k(cat)/K(M) for ATP and acetyl-CoA.

1-[2-[(5-Cyanopyridin-2-yl)amino]ethylamino]acetyl-2-(S)-pyrrolidinecarbonitrile: a potent, selective, and orally bioavailable dipeptidyl peptidase IV inhibitor with antihyperglycemic properties.

Dipeptidyl peptidase IV (DPP-IV) inhibition has the potential to become a valuable therapy for type 2 diabetes. We report the first use of solid-phase synthesis in the discovery of a new DPP-IV inhibitor class and a solution-phase synthesis that is practical up to the multikilogram scale. One compound, NVP-DPP728 (2), is profiled as a potent, selective, and short-acting DPP-IV inhibitor that has excellent oral bioavailability and potent antihyperglycemic activity.

Ordering the discipline: classification in the history of science. Introduction.

Classification of the history of science has a long history, and the essays in this Focus section explore that history and its consequences from several different angles. Two of the papers deal with how classifying schemes in bibliography have evolved. A third looks at the way archival organization has changed over the years. Finally, the last essay explores the intersection of human and machine classifying systems. All four contributions look closely at the ramifications of the digital revolution for the way we organize the knowledge of the discipline.

Organizing knowledge in the Isis bibliography from Sarton to the early twenty-first century.

This essay explores various ways in which bibliographies have exhibited "sociality." Bibliographies are both products of the social contexts that have created them and engines of social interaction in scholarly communities. By tracing the history of the Isis Bibliography, the longest-running and most comprehensive bibliography in its field, this essay explains how different Isis classification systems have been tied to major twentieth-century cataloging efforts. By looking at classification, the essay also attends to the ways in which aspects of the Isis Bibliography in different decades have reflected social mores of their period. Finally, it demonstrates how critical the Isis Bibliography was in the formation of the discipline of history of science and goes on to discuss how that disciplinary connection is evolving in the twenty-first century. By thinking of the bibliography as a network of scholars, not just scholarly works, the essay asks us to reflect on the nature and purpose of bibliography in the digital age.

Proteomic identification of ubiquitinated proteins from human cells expressing His-tagged ubiquitin.

A proteomics method has been developed to purify and identify the specific proteins modified by ubiquitin (Ub) from human cells. In purified samples, Ub and 21 other proteins were identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS) spectra using SEQUEST. These proteins included several of the expected carriers of Ub including Ub-conjugating enzymes and histone proteins. To perform these experiments, a cell line coexpressing epitope tagged His(6X)-Ub and green fluorescent protein (GFP) was generated by stably transfecting HEK293 cells. Ubiquitinated proteins were purified using nickel-affinity chromatography and digested in solution with trypsin. Complex mixtures of peptides were separated by reversed phase chromatography and analyzed by nano LC-MS/MS using the LCQ quadrupole ion-trap mass spectrometer. Proteins identified from His(6X)-Ub-GFP transfected cells were compared to a list of proteins from HEK293 cells, which associate with nickel-nitrilotriacetic acid (Ni-NTA)-agarose in the absence of His-tagged Ub. In a proof of principle experiment, His(6X)-Ub-GFP transfected cells were treated with As (III) (10 microM, 24 h) in an attempt to identify substrates increasingly modified by Ub. In this experiment, proliferating cell nuclear antigen, a DNA repair protein and known ubiquitin substrate, was confidently identified. This proteomics method, developed for the analysis of ubiquitinated proteins, is a step towards large-scale characterization of Ub-protein conjugates in numerous physiological and pathological states.

Advanced glycation end product ligands for the receptor for advanced glycation end products: biochemical characterization and formation kinetics.

Advanced glycation end products (AGEs) accumulate with age and at an accelerated rate in diabetes. AGEs bind cell-surface receptors including the receptor for advanced glycation end products (RAGE). The dependence of RAGE binding on specific biochemical characteristics of AGEs is currently unknown. Using standardized procedures and a variety of AGE measures, the present study aimed to characterize the AGEs that bind to RAGE and their formation kinetics in vitro. To produce AGEs with varying RAGE binding affinity, bovine serum albumin (BSA) AGEs were prepared with 0.5M glucose, fructose, or ribose at times of incubation from 0 to 12 weeks or for up to 3 days with glycolaldehyde or glyoxylic acid. The AGE-BSAs were characterized for RAGE binding affinity, fluorescence, absorbance, carbonyl content, reactive free amine content, molecular weight, pentosidine content, and N-epsilon-carboxymethyl lysine content. Ribose-AGEs bound RAGE with high affinity within 1 week of incubation in contrast to glucose- and fructose-AGE, which required 12 and 6 weeks, respectively, to generate equivalent RAGE ligands (IC50=0.66, 0.93, and 1.7 microM, respectively). Over time, all of the measured AGE characteristics increased. However, only free amine content robustly correlated with RAGE binding affinity. In addition, detailed protocols for the generation of AGEs that reproducibly bind RAGE with high affinity were developed, which will allow for further study of the RAGE-AGE interaction.