Biomedical subjects

L N Manganas

Publications and source records attributed to L N Manganas.

4 recordsLinked to original sources

PubMed2001

Identification of a trafficking determinant localized to the Kv1 potassium channel pore.

The repertoire of Kv1 potassium channels expressed in presynaptic terminals of mammalian central neurons is shaped by intrinsic trafficking signals that determine surface-expression efficiencies of homomeric and heteromeric Kv1 channel complexes. Here, we show that a determinant controlling surface expression of Kv1 channels is localized to the highly conserved pore region. Point-mutation analysis revealed two residues as critical for channel trafficking, one in the extracellular "turret" domain and one in the region distal to the selectivity filter. Interestingly, these same residues also form the binding sites for polypeptide neurotoxins. Our findings demonstrate a previously uncharacterized function for the channel-pore domain as a regulator of channel trafficking.

Amino Acid Sequence↗

PubMed2001

Episodic ataxia type-1 mutations in the Kv1.1 potassium channel display distinct folding and intracellular trafficking properties.

Episodic ataxia type 1 (EA-1) is a neurological disorder arising from mutations in the Kv1.1 potassium channel alpha-subunit. EA-1 patients exhibit substantial phenotypic variability resulting from at least 14 distinct EA-1 point mutations. We found that EA-1 missense mutations generate mutant Kv1.1 subunits with folding and intracellular trafficking properties indistinguishable from wild-type Kv1.1. However, the single identified EA-1 nonsense mutation exhibits intracellular aggregation and detergent insolubility. This phenotype can be transferred to co-assembled Kv1 alpha- and Kv beta-subunits associated with Kv1.1 in neurons. These results suggest that as in many neurodegenerative disorders, intracellular aggregation of misfolded Kv1.1-containing channels may contribute to the pathophysiology of EA-1.

Animals↗

PubMed2000

Subunit composition determines Kv1 potassium channel surface expression.

Shaker-related or Kv1 voltage-gated K(+) channels play critical roles in regulating the excitability of mammalian neurons. Native Kv1 channel complexes are octamers of four integral membrane alpha subunits and four cytoplasmic beta subunits, such that a tremendous diversity of channel complexes can be assembled from the array of alpha and beta subunits expressed in the brain. However, biochemical and immunohistochemical studies have demonstrated that only certain complexes predominate in the mammalian brain, suggesting that regulatory mechanisms exist that ensure plasma membrane targeting of only physiologically appropriate channel complexes. Here we show that Kv1 channels assembled as homo- or heterotetrameric complexes had distinct surface expression characteristics in both transfected mammalian cells and hippocampal neurons. Homotetrameric Kv1.1 channels were localized to endoplasmic reticulum, Kv1.4 channels to the cell surface, and Kv1.2 channels to both endoplasmic reticulum and the cell surface. Heteromeric assembly with Kv1.4 resulted in dose-dependent increases in cell surface expression of coassembled Kv1.1 and Kv1.2, while coassembly with Kv1.1 had a dominant-negative effect on Kv1.2 and Kv1.4 surface expression. Coassembly with Kv beta subunits promoted cell surface expression of each Kv1 heteromeric complex. These data suggest that subunit composition and stoichiometry determine surface expression characteristics of Kv1 channels in excitable cells.

Animals↗

PubMed2000

PSD-95 and SAP97 exhibit distinct mechanisms for regulating K(+) channel surface expression and clustering.

Mechanisms of ion channel clustering by cytoplasmic membrane-associated guanylate kinases such as postsynaptic density 95 (PSD-95) and synapse-associated protein 97 (SAP97) are poorly understood. Here, we investigated the interaction of PSD-95 and SAP97 with voltage-gated or Kv K(+) channels. Using Kv channels with different surface expression properties, we found that clustering by PSD-95 depended on channel cell surface expression. Moreover, PSD-95-induced clusters of Kv1 K(+) channels were present on the cell surface. This was most dramatically demonstrated for Kv1.2 K(+) channels, where surface expression and clustering by PSD-95 were coincidentally promoted by coexpression with cytoplasmic Kvbeta subunits. Consistent with a mechanism of plasma membrane channel-PSD-95 binding, coexpression with PSD-95 did not affect the intrinsic surface expression characteristics of the different Kv channels. In contrast, the interaction of Kv1 channels with SAP97 was independent of Kv1 surface expression, occurred intracellularly, and prevented further biosynthetic trafficking of Kv1 channels. As such, SAP97 binding caused an intracellular accumulation of each Kv1 channel tested, through the accretion of SAP97 channel clusters in large (3-5 microm) ER-derived intracellular membrane vesicles. Together, these data show that ion channel clustering by PSD-95 and SAP97 occurs by distinct mechanisms, and suggests that these channel-clustering proteins may play diverse roles in regulating the abundance and distribution of channels at synapses and other neuronal membrane specializations.

Adaptor Proteins, Signal Transducing↗