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K Kannenberg

Publications and source records attributed to K Kannenberg.

7 recordsLinked to original sources
PubMed2001

Interaction between GABA(A) receptor beta subunits and the multifunctional protein gC1q-R.

gamma-Aminobutyric acid type A (GABA(A)) receptors were immunopurified from bovine brain using a monoclonal antibody directed against the alpha1 subunit. Of the several proteins that copurified, a 34-kDa protein was analyzed further. After enrichment and tryptic proteolysis, the resulting fragments were sequenced, and the protein was identified as gC1q-R. Using anti-gC1q-R and anti-GABA(A) receptor antibodies, mutual coimmunoprecipitation could be demonstrated from solubilized rat brain membranes. The stability of this interaction was estimated to be very high. Using the yeast two-hybrid system, various GABA(A) receptor subunit intracellular loop constructs were tested for an interaction with gC1q-R. All beta subunits, but not alpha 1 and gamma 2 subunits, were found to bind to gC1q-R. NH(2)- and COOH-terminally truncated beta 2 subunit loops were used to find the region responsible for the interaction with gC1q-R. A stretch of 15 amino acids containing 7 positively charged residues was identified (amino acids 399--413). This region contains residue Ser-410, which is a protein kinase substrate, and it is known that phosphorylation of this residue leads to an alteration in receptor activity. Localization studies suggested a predominantly intracellular localization. Our observations therefore suggest a tight interaction between gC1q-R and the GABA(A) receptor which might be involved in receptor biosynthesis or modulation of the mature function.

Animals↗
PubMed1999

A novel serine kinase with specificity for beta3-subunits is tightly associated with GABA(A) receptors.

Tuning of gamma-aminobutyric acid type A (GABA(A)) receptor function via phosphorylation of the receptor potentially allows neurons to modulate their inhibitory input. Several kinases, both of the serine-threonine kinase and the tyrosine kinase families, have been proposed as candidates for such a modulatory role in vivo. However, no GABA(A) receptor-phosphorylating kinase physically associated with the receptor has been identified so far on a molecular level. In this study, we demonstrate a GABA(A) receptor-associated protein serine kinase phosphorylating specifically beta3-subunits of native GABA(A) receptors. The characteristics of this novel kinase clearly distinguish it from enzymatic activities that have been shown so far to phosphorylate the GABA(A) receptor. We putatively identify this protein kinase as the previously described GTAP34 (GABA(A) receptor-tubulin complex-associated protein of molecular mass 34 kDa). Using expressed recombinant fusion proteins, we identify serine 408 as a major target of the phosphorylation reaction, whereas serine 407 is not phosphorylated. This demonstrates the high specificity of the kinase. Phosphorylation of serine 408 is known to result in a decreased receptor function. The direct association of this kinase with the receptor indicates an important physiological role.

Animals↗
PubMed1999

Clusters of GABAA receptors on cultured hippocampal cells correlate only partially with functional synapses.

We describe a method to label gamma-aminobutyric acid (GABA)A receptors on the surface of living hippocampal neurons in primary culture, and we compare the distribution of receptors with that of active synapses. To visualize GABAA receptors, the affinity-purified antibody beta3(1-13), recognizing the extracellular N-termini of the GABAA receptor beta2- and beta3-subunits, was used in combination with fluorescent secondary antibodies. The beta2- and beta3-subunits belong to the predominant GABAA receptor subunits in the hippocampus. As expected for aggregates of GABAA receptors in the somato-dendritic plasma membrane, a patchy staining pattern similar to that seen by labelling neurons after fixation was obtained. An antiserum recognizing an intracellular epitope of GABAA receptor beta3-subunits did not label the receptors in living neurons. Whole-cell recordings of GABA-evoked Cl - currents were not affected after decorating GABAA receptors with antibody beta3(1-13). Combining the staining of GABAA receptors with the labelling of active presynaptic terminals with the fluorescent dyes FM1-43 or FM4-64, consistently resulted in the detection of GABAA receptor clusters that were not located at active synapses. These amounted to approximately 50% of all labelled GABAA receptor clusters. GABAA receptor clusters that were not associated with active presynaptic terminals partially colocalized with the synaptic vesicle marker protein sv2, while another fraction had no presynaptic counterpart at all. These findings suggest the presence of presynaptically silent GABAergic synapses in cultured hippocampal neurons. They also indicate that for the maintenance of GABAA receptor aggregates, the release of GABA from an opposing active terminal is not essential.

Animals↗
PubMed1997

Proteins associated with alpha 1-subunit-containing GABAA receptors from bovine brain.

In contrast to some other ion channels, there are at present no proteins known that bind specifically to mature GABAA receptor channels. Such proteins may be important for the structural organization and cytoskeletal anchoring of GABAA receptors and could also be expected to have channel modulatory effects. To identify proteins that are associated with naturally occurring GABAA receptors we immunoprecipitated these receptors from detergent-solubilized bovine brain membranes by an antibody directed against the alpha 1-subunit. Tubulin and actin were observed to coprecipitate specifically with the receptors. Nine additional proteins were detected, hinting at a complex protein network associated with alpha 1-subunit-containing GABAA receptors. Results of a biochemical characterization of these GABAA receptor-tubulin complex-associated proteins (GTAPs) are presented here. Peptide mass fingerprinting analysis and microsequencing of tryptic peptides indicated that at least three GTAPs have not been described until the present.

Actins↗
PubMed1995

Cellular prion protein and GABAA receptors: no physical association?

The so-called prion diseases are probably caused by the conformational conversion of the cellular prion protein (PrPc) into an abnormal, pathological form (PrPsc). PrPc is widely expressed in neuronal tissues, but its function is not known. From electrophysiological measurements in prion-less mice it was proposed that PrPc may contribute to the structural integrity of central synapses containing gamma-aminobutyric acid type A (GABAA) receptors. We tried to substantiate this hypothesis by obtaining evidence for a structural link between the GABAA receptor and PrPc. Preparations of PrPc and GABAA receptors, respectively, from cow brain were analysed for PrPc-GABAA receptor complexes. No evidence for such complexes could be obtained in our experiments, although the protein purification schemes used should favour the preservation of intermolecular linkages. We conclude that further data concerning interactions of PrPc with other proteins are needed to obtain insight into its normal functional role.

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