Ein einfaches Mikrokolorimeter

Ohne Zusammenfassung     

Conformational analysis of PKI(5-22)amide, the active inhibitory fragment of the inhibitor protein of the cyclic AMP-dependent protein kinase.

Fourier-transform i.r. spectroscopy, 1H-n.m.r. spectroscopy and X-ray scattering were used to study the conformation and shape of the peptide PKI(5-22)amide, which contains the active site of the inhibitor protein of the cyclic AMP-dependent protein kinase [Cheng, Van Pattern, Smith & Walsh (1985) Biochem. J. 231, 655-661]. The X-ray-scattering solution studies show that the peptide has a compact structure with Rg 0.9 nm (9.0 A) and a linear maximum dimension of 2.5 nm (25A). Compatible with this, Fourier-transform i.r. and n.m.r. determinations indicate that the peptide contains approx. 26% alpha-helix located in the N-terminal one-third of the molecule. This region contains the phenylalanine residue that is one essential recognition determinant for high-affinity binding to the protein kinase catalytic site.     

Biosynthesis and membrane topography of the neural cell adhesion molecule L1.

The biosynthesis and membrane topography of the neural cell adhesion molecule L1 have been studied in cerebellar cell cultures by metabolic labeling and immunoprecipitation. Pulse and pulse-chase experiments with [35S]methionine show that L1 is synthesized in its high mol. wt. form, the 200 kd component. The lower mol. wt. components with 40, 80 and 140 K apparent mol. wts. can be generated by proteolysis in intact cellular membranes. Peptide maps generated by protease treatment of L1 isolated from adult mouse brain show that the 80 and 140 kd components are related to the 200 kd component, but not to each other. The 200, 80 and 40 kd components can be biosynthetically phosphorylated. The 140 kd component is not phosphorylated and not released from the surface membrane during tryspinization. The phosphorylated amino acid is serine. In the presence of tunicamycin the 200 kd component is synthesized as a 150 kd protein. Pulse-chase experiments in the presence of tunicamycin indicate that the carbohydrate moieties are predominantly N-glycosidically linked and that the contribution of O-glycosylation is minimal. The carbohydrate moieties are of the complex type as shown by treatment with endoglycosidase H. Since monensin inhibits processing of the carbohydrate moieties, the 200 kd component appears to be transported to the surface membrane via the Golgi apparatus.     

Isolation and elucidation of some functional properties of the "mute" catalytic subunit of cAMP-dependent protein kinase

A mute isoenzyme of type II cAMP-dependent protein kinase from rat muscle has been reported that is released from the regulatory subunit by cAMP but remains inactive until combination with heat- and acid-stable modulator has occurred. This enzyme has now been obtained in isolation free of the normal catalytic subunit using affinity chromatography with both an ATP analog (Blue Dextran/Sepharose) and a protein substrate analog (Kemptide/CH-Sepharose). Separation can be effected in both cases before activation of the mute enzyme. Affinity of the mute enzyme for Blue Dextran--a ligand specific for the dinucleotide fold in this kinase--is somewhat higher than that of the normal enzyme. Conversely, before reaction with the modulatory protein the mute enzyme will not bind at all to Kemptide/CH-Sepharose, where the normal enzyme elutes at 50 mM KCl. When pretreated with the modulatory protein and so activated, mute enzyme binds to Kemptide with a very high affinity and can only be eluted using a natural substrate (phosphorylase kinase), up to 500 mM salt being ineffective. The modulator thus appears to act through alteration of the protein substrate binding site on the enzyme.     

Lebendbeobachtungen zur Struktur des Golgifeldes bei Zellen eines transplantablen Plasmocytoms in vitro

Zusammenfassung Zellen des aus unreifen Plasmoblasten bestehenden, transplantablen KG 13-Plasmocytoms des Goldhamsters zeigen bei phasenoptischer Lebendbeobachtung in vitro ein besonders großes, stark strukturiertes Golgifeld. Dieses wird von einem Saum heller Pinocytosetröpfchen gegen die Speichergranula abgesetzt. Die Form des Golgifeldes, die Gesetzmäßigkeit seiner Veränderungen, die Spezifität seiner Strukturen und seine Beziehung zum Zellkern werden beschrieben. Pinocytosebläschen wandern bei dieser Zellart im gesamten Verlauf sichtbar von der Zellmembran zwischen den Speichergranula hindurch zur Randzone des Golgifeldes und lösen sich dort auf. Die Granula des Cytoplasmas entstehen offenbar im Golgifeld und werden in seiner Randzone erstmalig als solche erkennbar, um ins Cytoplasma zu wandern.

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Summary The KG 13 plasmocytoma from the Syrian golden hamster consists of immature Plasmoblasts. Living cells of this plasmocytoma observed by phase contrast microscopy in the hanging drop in vitro have a particularly large Golgi field surrounded by a border of light pinocytose bubbles. The cytoplasma is filled with storage granules. The form and the modifications of the Golgi field are described as well as his structure and his relations to the nucleus. Pinocytose bubbles reach the border of the Golgi field after crossing granules and disappeare. The granules are evidently formed in the Golgi field and become visible in its periphery.

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Die Arbeit wurde mit Unterstützung durch die Deutsche Forschungsgemeinschaft durchgeführt.     

Solvent polarity-dependent structural refolding: A CD and NMR study of a 15 residue peptide

A close association between the HIV surface protein gp120 and the CD4 T cell receptor initiates the viral multiplication cycle. A 15 amino acid peptide (LAV) within the CD4 binding domain of gp 120 has been shown to retain receptor binding ability. The structural behavior of the LAV peptide has been studied by CD and NMR methods in aqueous solution and upon addition of trifluoroethanol (TFE) to emulate the relatively apolar conditions at the membrane bound receptor. Previous work has shown that the LAV peptide folds into a β-pleated structure in more polar buffer/TFE mixtures, while a concerted structural change can be observed at a concentration of 60% TFE (v/v). This abrupt, cooperative refolding from a regular β-sheet to a helical secondary structure is known as “switch” behavior. Former CD experiments with LAV sequence variants have supported the assumption that four amino acids at the N-terminus (LPCR) are indispensable for the “switch.” The tetrad has a strong β-turn forming potential. The suggestion has been formulated that the tetrad can act as a nucleation site governing the refolding. The present NMR study of the LAV peptide in TFE gives evidence for a 3₁₀-helix suggesting that the tetrad adopts a type III β-turn and promotes the formation of a similar bend in the next overlapping tetrad until the sequence is restructured into a 3₁₀-helix at a critical polarity favoring intrachain hydrogen bonds. © 1995 Wiley-Liss, Inc.     

Protein kinase activity and substrates at the surface of intact HeLa cells

Evidence is presented for the location at the surface of HeLa cells of a protein kinase capable of phosphorylating surface as well as extracellular (foreign) proteins. The reaction products have been found to be proteins containing phosphoryl groups as monoesters of seryl and threonyl residues (but not of tyrosine). The enzyme is of the cyclic AMP-independent type, since neither cyclic AMP nor the heat- and acid-stable inhibitor protein (specific for cyclic AMP-dependent protein kinases) influenced its activity. Further, co-substrate ATP could in part be substituted by GTP, and the spectrum of proteins phosphorylated by the ecto-enzyme differed from that phosphorylated by cyclic AMP-dependent protein kinases. Evidence for the ecto-enzymic nature of this protein kinase includes (a) utilization of co-substrate and location of products at the surface of cells carefully controlled as being in an intact state and (b) phosphorylation of exogenous protein (phosvitin; specific serum proteins) by intact cells. Conclusive proof was gained by qualitative and quantitative comparative studies of phosphorylation in cultures with varying degrees of damaged cells either as a whole or after separation into groups of intact and damaged cells by electronic cell sorting. The results of experiments with cell sonicates excluded the possibility that either enzyme or substrates released from damaged cells were simply adsorbing to the cell surface.     

Referate

Ohne Zusammenfassung     

A Hypomorphic Lsd1 Allele Results in Heart Development Defects in Mice

Lysine-specific demethylase 1 (Lsd1/Aof2/Kdm1a), the first enzyme with specific lysine demethylase activity to be described, demethylates histone and non-histone proteins and is essential for mouse embryogenesis. Lsd1 interacts with numerous proteins through several different domains, most notably the tower domain, an extended helical structure that protrudes from the core of the protein. While there is evidence that Lsd1-interacting proteins regulate the activity and specificity of Lsd1, the significance and roles of such interactions in developmental processes remain largely unknown. Here we describe a hypomorphic Lsd1 allele that contains two point mutations in the tower domain, resulting in a protein with reduced interaction with known binding partners and decreased enzymatic activity. Mice homozygous for this allele die perinatally due to heart defects, with the majority of animals suffering from ventricular septal defects. Molecular analyses revealed hyperphosphorylation of E-cadherin in the hearts of mutant animals. These results identify a previously unknown role for Lsd1 in heart development, perhaps partly through the control of E-cadherin phosphorylation.