Friedrich Lottspeich

A multiprotein complex mediates the ATP-dependent assembly of spliceosomal U snRNPs

The spliceosomal snRNPs U1, U2, U4 and U5 contain a common RNP structure termed the Sm core that is formed by the binding of Sm proteins onto the U snRNA. Although isolated Sm proteins assemble spontaneously onto U snRNAs in vitro, there is increasing evidence that SMN and its interactor Gemin2 are involved in this process in vivo. Here, we describe a cell-free assay system for the assembly of U snRNPs that closely reproduces in vivo conditions. Using this system, we show that assembly of U1 snRNP depends on ATP. Immunodepletion of SMN–Gemin2 from the extract abolished assembly even though the extract contained high levels of Sm proteins. An affinity-purified macromolecular SMN complex consisting of 16 components including all Sm proteins restored assembly in the immunodepleted extract. These data provide the first direct evidence that a complex containing SMN and Gemin2 mediates the active assembly of spliceosomal U snRNPs.

Cloning, molecular and functional characterization of Arabidopsis thaliana allene oxide synthase (cyp 74), the first enzyme of the octadecanoid pathway to jasmonates.

Allene oxide synthase, an enzyme of the octadecanoid pathway to jasmonates, was cloned from Arabidopsis thaliana as a full-length cDNA encoding a polypeptide of 517 amino acids with a calculated molecular mass of 58705 Da. From the sequence, an N-terminal transit peptide of 21 amino acids resembling chloroplast transit peptides was deduced. Three out of four invariant amino acid residues of cytochrome P450 heme-binding domains are conserved and properly positioned in the enzyme coding region, including the heme-accepting cysteine (Cys-470). Southern analysis indicated in A. thaliana only one allene oxide synthase gene to be present. While transcript levels were rapidly and transiently induced after wounding of the leaves, allene oxide synthase activity remained nearly constant at a low level of ca. 0.8 nkat per mg of protein. The cDNA encoding A. thaliana allene oxide synthase was highly expressed in bacteria giving rise to a polypeptide of the calculated molecular mass. The protein was enzymatically active, and verification of the reaction products by GC-MS showed that it was capable of utilizing not only 13-hydroperoxylinolenic acid (13-hydroperoxy-9(Z), 11(E), 15(Z)-octadecatrienoic acid), but also 13-hydroperoxylinoleic acid (13-hydroperoxy-9(Z), 11(E)-octadecadienoic acid) as substrate. The data suggest parallel pathways to jasmonates from linolenic acid or linoleic acid in A. thalina.

The ion channel of the nicotinic acetylcholine receptor is formed by the homologous helices M II of the receptor subunits.

A binding site for the channel‐blocking noncompetitive antagonist [3H]triphenylmethylphosphonium ([3H]TPMP+) was localized in the α‐, β‐ and δ‐chains of the nicotinic acetylcholine receptor (AChR) from Torpedo marmorata electric tissue. The photolabel was found in homologous positions of the highly conserved sequence helix II, α 248, β 254, and δ 262. The site of the photoreaction appears to not be affected by the functional state of the receptor. [3H]TPMP+ was found in position δ 262 independent of whether photolabeling was performed with the receptor in its resting, desensitized or antagonist state. A model of the AChR ion channel is proposed, according to which the channel is formed by the five helices II contributed by the five receptor subunits.

Isolation of an RNA-Directed RNA Polymerase–Specific cDNA Clone from Tomato

A 3600-bp RNA-directed RNA polymerase (RdRP)–specific cDNA comprising an open reading frame (ORF) of 1114 amino acids was isolated from tomato. The putative protein encoded by this ORF does not share homology with any characterized proteins. Antibodies that were raised against synthetic peptides whose sequences have been deduced from the ORF were shown to specifically detect the 127-kD tomato RdRP protein. The immunoresponse to the antibodies correlated with the enzymatic activity profile of the RdRP after chromatography on Q-, poly(A)–, and poly(U)–Sepharose, hydroxyapatite, and Sephadex G-200 columns. DNA gel blot analysis revealed a single copy of the RdRP gene in tomato. RdRP homologs from petunia, Arabidopsis, tobacco, and wheat were identified by using polymerase chain reaction. A sequence comparison indicated that sequences homologous to RdRP are also present in the yeast Schizosaccharomyces pombe and in the nematode Caenorhabditis elegans. The previously described induction of RdRP activity upon viroid infection is shown to be correlated with an increased steady state level of the corresponding mRNA. The possible involvement of this heretofore functionally elusive plant RNA polymerase in homology-dependent gene silencing is discussed.

Synaptic vesicles immunoisolated from rat cerebral cortex contain high levels of glutamate.

L-Glutamate is regarded as the major excitatory neurotransmitter in the mammalian CNS. However, whether the released transmitter originates from a cytosolic pool or is discharged from synaptic vesicles by exocytosis (vesicle hypothesis) remains controversial. A problem with the general acceptance of the vesicle hypothesis is that the enrichment of glutamate in synaptic vesicles has not been convincingly demonstrated. In the present study, we have analyzed the glutamate content of synaptic vesicles isolated from rat cerebral cortex by a novel immunobead procedure. A large amount of glutamate was present in these vesicles when a proton electrochemical gradient was maintained across the vesicle membrane during isolation. Compared with the starting fraction, glutamate was enriched more than 10-fold relative to other amino acids. Addition of N-ethylmaleimide prevented glutamate loss during isolation. Isotope exchange experiments revealed that exchange or re-uptake of glutamate after homogenization is negligible. We conclude that rat brain synaptic vesicles contain high levels of glutamate in situ.

The 'light' and 'medium' subunits of the photosynthetic reaction centre from Rhodopseudomonas viridis: isolation of the genes, nucleotide and amino acid sequence.

The ‘light’ (L) and the ‘medium’ (M) subunits of the photosynthetic reaction centre from Rhodopseudomonas viridis were isolated and their amino‐terminal sequences, as well as the sequences of several chymotryptic peptides, determined. Rps. viridis DNA was cloned in the Escherichia coli plasmid pBR322. Mixed oligonucleotide probes derived from the amino acid sequences were synthesised and utilised to isolate one clone which contained the genes for the L and M subunits of the reaction centre as well as the α and β subunits of the light‐harvesting complex and part of the gene for the reaction centre cytochrome. The nucleotide sequences of the L and M subunit genes and the derived amino acid sequences are presented. The L subunit consists of 273 amino acids and has a mol. wt of 30 571. The M subunit consists of 323 amino acids and has a mol. wt of 35 902. The primary structure is discussed in the light of the recently published secondary and tertiary structure which has shown that both subunits contain five membrane‐spanning helices.

COVALENT STRUCTURE OF FIBRINOGEN

It is well established that the fibrinogen molecule is made up of two identical halves, each containing three different peptide chains. The overall structure may therefore be described as (Aa, Bp, y ) 2. On thrombin-digestion the fibrinopeptides A and B are released and fibrin, with the structure (a, p, yl2, is formed. The complete primary structure of human fibrinogen is known.l-16 The sequence information may be used to study relationships between structure, function and evolution. In genetically determined abnormal fibrinogens the correlation between the structural error and the dysfunction of the molecule may reveal the functional importance of single amino acid residues.

Brain derived neurotrophic factor

ZusammenfassungDer „brain-derived neurotrophic factor“ (BDNF) gehört zur Familie der Neurotrophine und spielt eine wichtige Rolle beim axonalen und dendritischen Wachstum von Neuronen und der Gehirnplastizität. Die Proform von BDNF (pro-BDNF) wird in den synaptischen Spalt ausgeschüttet und dort durch die Protease Plasmin zum maturen BDNF abgebaut. BDNF fördert die synaptische Plastizität und eine Langzeitpotenzierung. Neuere Untersuchungsergebnisse deuten auf eine Beteiligung von BDNF und dessen genetischer funktioneller Polymorphismen bei der Pathogenese verschiedener psychischer Erkrankungen wie z. B. Depression, Manie, Schizophrenie, Essstörungen, Demenz und Huntington-Erkrankung hin. Die BDNF-Konzentration im Gehirn, aber auch im Serum wird durch verschiedene Faktoren beeinflusst. Sie ist z. B. durch Stress vermindert und wird durch Lernprozesse, verschiedene antidepressive Therapiemodalitäten, körperliche Aktivität und Diät erhöht. Die Bestimmung der BDNF-Serumspiegel könnte diagnostische Bedeutung erlangen. Daneben könnte die gezielte Beeinflussung der BDNF-Verfügbarkeit durch verschiedene Maßnahmen eine Relevanz zur Therapie und möglicherweise auch zur Prävention oben genannter psychischer Krankheitsbilder gewinnen.SummaryBrain-derived neurotrophic factor (BDNF) is a member of the neurotrophin family and plays an important role in neuronal survival and plasticity in the CNS. The proform of BDNF (pro-BDNF) is secreted and cleaved extracellularly by the serine protease plasmin to mature BDNF, which potentiates synaptic plasticity and long-term potentiation. Recent findings in animal models suggest an involvement of BDNF and its genetic functional single nucleotide polymorphism in the pathogenesis of different psychiatric diseases including depression, mania, schizophrenia, eating disorders, dementia, and Huntington’s disease. In the brain and serum, BDNF is modulated by different factors. It is downregulated by stress and upregulated by learning processes, several antidepressive treatments, physical activity, and dietary restriction. Measurement of BDNF serum concentrations may be of diagnostic value. Additionally, the influence of different strategies for BDNF allocation seems to be relevant for the treatment and prevention of the above psychiatric disorders.

Inhibition of HIV-1 replication in lymphocytes by mutants of the Rev cofactor eIF-5A.

Eukaryotic initiation factor 5A (eIF-5A) is a cellular cofactor required for the function of the human immunodeficiency virus type-1 (HIV-1) Rev trans-activator protein. The majority of a set of eIF-5A mutants did not support growth of yeast cells having an inactivated genomic copy of eIF-5A, indicating that the introduced mutation eliminated eIF-5A activity. Two nonfunctional mutants, eIF-5AM13 and eIF-5AM14, retained their binding capacity for the HIV-1 Rev response element: Rev complex. Both mutants were constitutively expressed in human T cells. When these T cells were infected with replication-competent HIV-1, virus replication was inhibited. The eIF-5AM13 and eIF-5AM14 proteins blocked Rev trans-activation and Rev-mediated nuclear export.

Matching of oligoclonal immunoglobulin transcriptomes and proteomes of cerebrospinal fluid in multiple sclerosis

We describe a method for correlating the immunoglobulin (Ig) proteomes with the B cell transcriptomes in human fluid and tissue samples, using multiple sclerosis as a paradigm. Oligoclonal Ig bands and elevated numbers of clonally expanded B cells in the cerebrospinal fluid (CSF) are diagnostic hallmarks of multiple sclerosis. Here we compared the Ig transcriptomes of B cells with the corresponding Ig proteomes in CSF samples from four subjects with multiple sclerosis. We created individual Ig transcriptome databases that contained the subject-specific mutations introduced by V(D)J recombination and somatic hypermutation and then searched the CSF for corresponding characteristic peptides by mass spectrometry. In each sample, the Ig transcriptomes and proteomes strongly overlapped, showing that CSF B cells indeed produce the oligoclonal Ig bands. This approach can be applied to other organ-specific diagnostic fluid or tissue samples to compare the Ig transcripts of local B cells with the corresponding antibody proteomes of individual subjects.