Medical Biochemistry Commons^™

The 40-Residue Insertion In Vibrio Cholerae Fadr Facilitates Binding Of An Additional Fatty Acyl-Coa Ligand, Wei Shi, Gabriela Kovacikova, Wei Lin, Ronald. K. Taylor, Karen Skorupski, F. Jon Kull

Dartmouth Scholarship

FadR is a master regulator of fatty acid metabolism and influences virulence in certain members of Vibrionaceae. Among FadR homologues of the GntR family, the Vibrionaceae protein is unusual in that it contains a C-terminal 40-residue insertion. Here we report the structure of Vibrio cholerae FadR (VcFadR) alone, bound to DNA, and in the presence of a ligand, oleoyl-CoA. Whereas Escherichia coli FadR (EcFadR) contains only one acyl-CoA-binding site in each monomer, crystallographic and calorimetric data indicate that VcFadR has two. One of the binding sites resembles that of EcFadR, whereas the other, comprised residues from the insertion, has not …

Sec17 Can Trigger Fusion Of Trans-Snare Paired Membranes Without Sec18, Michael Zick, Amy Orr, Matthew L. Schwartz, Alexey J. Merz, William Wickner

Dartmouth Scholarship

Sec17 [soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein; α-SNAP] and Sec18 (NSF) perform ATP-dependent disassembly of cis-SNARE complexes, liberating SNAREs for subsequent assembly of trans-complexes for fusion. A mutant of Sec17, with limited ability to stimulate Sec18, still strongly enhanced fusion when ample Sec18 was supplied, suggesting that Sec17 has additional functions. We used fusion reactions where the four SNAREs were initially separate, thus requiring no disassembly by Sec18. With proteoliposomes bearing asymmetrically disposed SNAREs, tethering and trans-SNARE pairing allowed slow fusion. Addition of Sec17 did not affect the levels of trans-SNARE complex but triggered sudden fusion of trans-SNARE paired proteoliposomes. …

Fungal Mediator Tail Subunits Contain Classical Transcriptional Activation Domains, Zhongle Liu, Lawrence C. Myers

Dartmouth Scholarship

Classical activation domains within DNA-bound eukaryotic transcription factors make weak interactions with coactivator complexes, such as Mediator, to stimulate transcription. How these interactions stimulate transcription, however, is unknown. The activation of reporter genes by artificial fusion of Mediator subunits to DNA binding domains that bind to their promoters has been cited as evidence that the primary role of activators is simply to recruit Mediator. We have identified potent classical transcriptional activation domains in the C termini of several tail module subunits of Saccharomyces cerevisiae, Candida albicans, and Candida dubliniensis Mediator, while their N-terminal domains are necessary and sufficient for their …

Interactions Of Peptide Triazole Thiols With Env Gp120 Induce Irreversible Breakdown And Inactivation Of Hiv-1 Virions, Arangassery Bastian, Mark Contarino, Lauren D. Bailey, Rachna Aneja, Diogo Rodrigo Magalhaes Moreira, Kevin Freedman, Karyn Mcfadden, Caitlin Duffy, Ali Emileh

Dartmouth Scholarship

Background: We examined the underlying mechanism of action of the peptide triazole thiol, KR13 that has been shown previously to specifically bind gp120, block cell receptor site interactions and potently inhibit HIV-1 infectivity.

Results: KR13, the sulfhydryl blocked KR13b and its parent non-sulfhydryl peptide triazole, HNG156, induced gp120 shedding but only KR13 induced p24 capsid protein release. The resulting virion post virolysis had an altered morphology, contained no gp120, but retained gp41 that bound to neutralizing gp41 antibodies. Remarkably, HIV-1 p24 release by KR13 was inhibited by enfuvirtide, which blocks formation of the gp41 6-helix bundle during membrane fusion, while …

Cofactor Molecules Maintain Infectious Conformation And Restrict Strain Properties In Purified Prions, Nathan R. Deleault, Daniel J. Walsh, Justin R. Piro, Fei Wang, Xinhe Wang, Jiyan Ma, Judy R. Rees, Surachai Supattapone

Dartmouth Scholarship

No abstract provided.

Isolation Of Phosphatidylethanolamine As A Solitary Cofactor For Prion Formation In The Absence Of Nucleic Acids, Nathan R. Deleault, Justin R. Piro, Daniel J. Walsh, Fei Wang, Jiyan Ma, James C. Geoghegan, Surachai Supattapone

Dartmouth Scholarship

Infectious prions containing the pathogenic conformer of the mammalian prion protein (PrP(Sc)) can be produced de novo from a mixture of the normal conformer (PrP(C)) with RNA and lipid molecules. Recent reconstitution studies indicate that nucleic acids are not required for the propagation of mouse prions in vitro, suggesting the existence of an alternative prion propagation cofactor in brain tissue. However, the identity and functional properties of this unique cofactor are unknown. Here, we show by purification and reconstitution that the molecule responsible for the nuclease-resistant cofactor activity in brain is endogenous phosphatidylethanolamine (PE). Synthetic PE alone facilitates conversion of …

Structure Of Vibrio Cholerae Toxt Reveals A Mechanism For Fatty Acid Regulation Of Virulence Genes, Michael J. Lowden, Karen Skorupski, Maria Pellegrini, Michael G. Chiorazzo, Ronald K. Taylor, F. Jon Kull

Dartmouth Scholarship

Cholera is an acute intestinal infection caused by the bacterium Vibrio cholerae. In order for V. cholerae to cause disease, it must produce two virulence factors, the toxin-coregulated pilus (TCP) and cholera toxin (CT), whose expression is controlled by a transcriptional cascade culminating with the expression of the AraC-family regulator, ToxT. We have solved the 1.9 A resolution crystal structure of ToxT, which reveals folds in the N- and C-terminal domains that share a number of features in common with AraC, MarA, and Rob as well as the unexpected presence of a buried 16-carbon fatty acid, cis-palmitoleate. The finding that …

Assays Of Vacuole Fusion Resolve The Stages Of Docking, Lipid Mixing, And Content Mixing, Youngsoo Jun, William Wickner

Dartmouth Scholarship

Membrane fusion entails organelle docking and subsequent mixing of membrane bilayers and luminal compartments. We now present an in vitro assay of fusion, using yeast vacuoles bearing domains of either Fos or Jun fused to complementary halves of beta-lactamase. Upon fusion, these proteins associate to yield beta-lactamase activity. This assay complements the standard fusion assay (activation of pro-Pho8p in protease-deficient vacuoles by proteases from pho8Delta vacuoles). Both the beta-lactamase and pro-Pho8p activation assays of fusion show the same long kinetic delay between SNARE pairing and luminal compartment mixing. Lipid-mixing occurs rapidly after SNARE pairing but well before aqueous compartment mixing. …

P53 Activation By Knockdown Technologies, Mara E. Robu, Jon D. Larson, Aidas Nasevicius, Soraya Beiraghi, Charles Brenner

Dartmouth Scholarship

Morpholino phosphorodiamidate antisense oligonucleotides (MOs) and short interfering RNAs (siRNAs) are commonly used platforms to study gene function by sequence-specific knockdown. Both technologies, however, can elicit undesirable off-target effects. We have used several model genes to study these effects in detail in the zebrafish, Danio rerio. Using the zebrafish embryo as a template, correct and mistargeting effects are readily discernible through direct comparison of MO-injected animals with well-studied mutants. We show here indistinguishable off-targeting effects for both maternal and zygotic mRNAs and for both translational and splice-site targeting MOs. The major off-targeting effect is mediated through p53 activation, as detected …

Trans-Snare Complex Assembly And Yeast Vacuole Membrane Fusion, Kevin M. Collins, William T. Wickner

Dartmouth Scholarship

cis-SNARE complexes (anchored in one membrane) are disassembled by Sec17p (α-SNAP) and Sec18p (NSF), permitting the unpaired SNAREs to assemble in trans. We now report a direct assay of trans-SNARE complex formation during yeast vacuole docking. SNARE complex assembly and fusion is promoted by high concentrations of the SNARE Vam7p or Nyv1p or by addition of HOPS (homotypic fusion and vacuole protein sorting), a Ypt7p (Rab)-effector complex with a Sec1/Munc18-family subunit. Inhibitors that target Ypt7p, HOPS, or key regulatory lipids prevent trans-SNARE complex assembly and ensuing fusion. Strikingly, the lipid ligand MED (myristoylated alanine-rich C kinase substrate effector domain) or …

Binding Between The Niemann–Pick C1 Protein And A Photoactivatable Cholesterol Analog Requires A Functional Sterol-Sensing Domain, Nobutaka Ohgami, Dennis C. Ko, Matthew Thomas, Matthew P. Scott, Catherine C. Y. Chang, Ta-Yuan Chang

Dartmouth Scholarship

Niemann-Pick type C (NPC) 1 protein plays important roles in moving cholesterol and other lipids out of late endosomes by means of vesicular trafficking, but it is not known whether NPC1 directly interacts with cholesterol. We performed photoaffinity labeling of intact cells expressing fluorescent protein (FP)-tagged NPC1 by using [(3)H]7,7-azocholestanol ([(3)H]AC). After immunoprecipitation, (3)H-labeled NPC1-GFP appeared as a single band. Including excess unlabeled sterol to the labeling reaction significantly diminished the labeling. Altering the NPC1 sterol-sensing domain (SSD) with loss-of-function mutations (P692S and Y635C) severely reduced the extent of labeling. To further demonstrate the specificity of labeling, we show that …

The Tumor Suppressor Lkb1 Kinase Directly Activates Amp-Activated Kinase And Regulates Apoptosis In Response To Energy Stress, Reuben J. Shaw, Monica Kosmatka, Nabeel Bardeesy, Rebecca L. Hurley, Lee A. Witters, Ronald A. Depinho, Lewis C. Cantley

Dartmouth Scholarship

AMP-activated protein kinase (AMPK) is a highly conserved sensor of cellular energy status found in all eukaryotic cells. AMPK is activated by stimuli that increase the cellular AMP/ATP ratio. Essential to activation of AMPK is its phosphorylation at Thr-172 by an upstream kinase, AMPKK, whose identity in mammalian cells has remained elusive. Here we present biochemical and genetic evidence indicating that the LKB1 serine/threonine kinase, the gene inactivated in the Peutz-Jeghers familial cancer syndrome, is the dominant regulator of AMPK activation in several mammalian cell types. We show that LKB1 directly phosphorylates Thr-172 of AMPKalpha in vitro and activates its …

Copper Chelation Represses The Vascular Response To Injury, Lazar Mandinov, Anna Mandinova, Stanimir Kyurkchiev, Dobroslav Kyurkchiev, Ivan Kehayov, Vihren Kolev, Raffaella Soldi, Cinzia Bagala, Ebo D. De Muinck, Volkhard Lindner, Mark J. Post, Michael Simons

Dartmouth Scholarship

The induction of an acute inflammatory response followed by the release of polypeptide cytokines and growth factors from peripheral blood monocytes has been implicated in mediating the response to vascular injury. Because the Cu2+-binding proteins IL-1alpha and fibroblast growth factor 1 are exported into the extracellular compartment in a stress-dependent manner by using intracellular Cu2+ to facilitate the formation of S100A13 heterotetrameric complexes and these signal peptideless polypeptides have been implicated as regulators of vascular injury in vivo, we examined the ability of Cu2+ chelation to repress neointimal thickening in response to injury. We observed that the oral administration of …

Analysis Of Mitotic Microtubule-Associated Proteins Using Mass Spectrometry Identifies Astrin, A Spindle-Associated Protein, Gary J. Mack, Duane A. Compton

Dartmouth Scholarship

We purified microtubules from a mammalian mitotic extract and obtained an amino acid sequence from each microtubule-associated protein by using mass spectrometry. Most of these proteins are known spindle-associated components with essential functional roles in spindle organization. We generated antibodies against a protein identified in this collection and refer to it as astrin because of its association with astral microtubule arrays assembled in vitro. Astrin is approximately 134 kDa, and except for a large predicted coiled-coil domain in its C-terminal region it lacks any known functional motifs. Astrin associates with spindle microtubules as early as prophase where it concentrates at …

The Chromokinesin Kid Is Necessary For Chromosome Arm Orientation And Oscillation, But Not Congression, On Mitotic Spindles, Aime A. Levesque, Duane A. Compton

Dartmouth Scholarship

Chromokinesins have been postulated to provide the polar ejection force needed for chromosome congression during mitosis. We have evaluated that possibility by monitoring chromosome movement in vertebrate-cultured cells using time-lapse differential interference contrast microscopy after microinjection with antibodies specific for the chromokinesin Kid. 17.5% of cells injected with Kid-specific antibodies have one or more chromosomes that remain closely opposed to a spindle pole and fail to enter anaphase. In contrast, 82.5% of injected cells align chromosomes in metaphase, progress to anaphase, and display chromosome velocities not significantly different from control cells. However, injected cells lack chromosome oscillations, and chromosome orientation …

Circadian Clock-Specific Roles For The Light Response Protein White Collar-2, Michael A. Collett, Jay C. Dunlap, Jennifer J. Loros

Dartmouth Scholarship

To understand the role of white collar-2 in theNeurospora circadian clock, we examined alleles ofwc-2 thought to encode partially functional proteins. We found that wc-2 allele ER24 contained a conservative mutation in the zinc finger. This mutation results in reduced levels of circadian rhythm-critical clock gene products, frq mRNA and FRQ protein, and in a lengthened period of the circadian clock. In addition, this mutation altered a second canonical property of the clock, temperature compensation: as temperature increased, period length decreased substantially. This temperature compensation defect correlated with a temperature-dependent increase in overall FRQ protein levels, with the …

Three V-Snares And Two T-Snares, Present In A Pentameric Cis-Snare Complex On Isolated Vacuoles, Are Essential For Homotypic Fusion, Christian Ungermann, Gabriele F. Von Mollard, Ole N. Jensen, Nathan Margolis, Tom H. Stevens, William Wickner

Dartmouth Scholarship

Vacuole SNAREs, including the t-SNAREs Vam3p and Vam7p and the v-SNARE Nyv1p, are found in a multisubunit "cis" complex on isolated organelles. We now identify the v-SNAREs Vti1p and Ykt6p by mass spectrometry as additional components of the immunoisolated vacuolar SNARE complex. Immunodepletion of detergent extracts with anti-Vti1p removes all the Ykt6p that is in a complex with Vam3p, immunodepletion with anti-Ykt6p removes all the Vti1p that is complexed with Vam3p, and immunodepletion with anti-Nyv1p removes all the Ykt6p in complex with other SNAREs, demonstrating that they are all together in the same cis multi-SNARE complex. After priming, which disassembles …

Subunit Dynamics In Escherichia Coli Preprotein Translocase., John C. Joly, Marilyn R. Leonard, William T. Wickner

Dartmouth Scholarship

SecY, SecE, and band 1 copurify as the SecY/E integral membrane domain of Escherichia coli preprotein translocase. To measure the in vivo association of these polypeptides and assay possible exchange, plasmid-borne secY and secE genes were placed under control of the ara regulon and fused to DNA encoding the influenza hemagglutinin epitope. Cells were incubated with [35S]methionine, grown for a "chase" period, and then induced with arabinose to express epitope-tagged, nonradioactive SecY and SecE. Both the wild-type and epitope-tagged polypeptides assembled into functional, heterotrimeric SecY/E complex. However, immunoprecipitation with antibody to the epitope tag did not cross-precipitate radiolabeled SecY or …

A Phorbol Ester Response Element Within The Human T-Cell Receptor Beta-Chain Enhancer., Haydn M. Prosser, David Wotton, Anne Gegonne, Jacques Ghysdael, Shuwen Wang, Nancy A. Speck, Michael J. Owen

Dartmouth Scholarship

The activity of the T-cell receptor beta-chain gene enhancer is increased by activators of the protein kinase C pathway during T-cell activation. Analysis of mutant enhancer constructs identified two elements, beta E2 and beta E3, conferring phorbol ester inducibility. Multimerized beta E2 acted in isolation as a phorbol ester-responsive element. Both beta E2 and beta E3, which contain a consensus Ets-binding site, were shown to bind directly to the product of the c-ets-1 protooncogene. Both regions also bound a second factor, core-binding factor. Mutation of the beta E2 Ets site abolished the inducibility of the beta E2 multimer. beta E2 …