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Tetanus toxin is internalized by a sequential clathrin-dependent mechanism initiated within lipid microdomains and independent of epsin1.

ABSTRACT: Ligand-receptor complexes are internalized by a variety of endocytic mechanisms. Some are initiated within clathrin-coated membranes, whereas others involve lipid microdomains of the plasma membrane. In neurons, where alternative targeting to short- or long-range trafficking routes underpins the differential processing of synaptic vesicle components and neurotrophin receptors, the mechanism giving access to the axonal retrograde pathway remains unknown. To investigate this sorting process, we examined the internalization of a tetanus neurotoxin fragment (TeNT HC), which shares axonal carriers with neurotrophins and their receptors. Previous studies have shown that the TeNT HC receptor, which comprises polysialogangliosides, resides in lipid microdomains. We demonstrate that TeNT HC internalization also relies on a specialized clathrin-mediated pathway, which is independent of synaptic vesicle recycling. Moreover, unlike transferrin uptake, this AP-2-dependent process is independent of epsin1. These findings identify a pathway for TeNT, beginning with the binding to a lipid raft component (GD1b) and followed by dissociation from GD1b as the toxin internalizes via a clathrin-mediated mechanism using a specific subset of adaptor proteins.

SUBMITTER: Deinhardt K

PROVIDER: S-EPMC2064241 | biostudies-literature | 2006 Jul

REPOSITORIES: biostudies-literature

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Tetanus toxin is internalized by a sequential clathrin-dependent mechanism initiated within lipid microdomains and independent of epsin1.

Deinhardt Katrin K Berninghausen Otto O Willison Hugh J HJ Hopkins Colin R CR Schiavo Giampietro G

The Journal of cell biology 20060701 3

Ligand-receptor complexes are internalized by a variety of endocytic mechanisms. Some are initiated within clathrin-coated membranes, whereas others involve lipid microdomains of the plasma membrane. In neurons, where alternative targeting to short- or long-range trafficking routes underpins the differential processing of synaptic vesicle components and neurotrophin receptors, the mechanism giving access to the axonal retrograde pathway remains unknown. To investigate this sorting process, we ex ...[more]

PMID: 16880274

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Project description:The clostridial neurotoxins (CNTs) comprise tetanus toxin (TT) and botulinum neurotoxin (BoNT [BT]) serotypes (A to G and X) and several recently identified CNT-like proteins, including BT/En and the mosquito BoNT-like toxin Pmp1. CNTs are produced as single proteins cleaved to a light chain (LC) and a heavy chain (HC) connected by an interchain disulfide bond. LC is a zinc metalloprotease (cleaving soluble N-ethylmaleimide-sensitive factor attachment protein receptors [SNAREs]), while HC contains an N-terminal translocation domain (HCN) and a C-terminal receptor binding domain (HCC). HCN-mediated LC translocation is the least understood function of CNT action. Here, ?-lactamase (?lac) was used as a reporter in discovery-based live-cell assays to characterize TT-mediated LC translocation. Directed mutagenesis identified a role for a charged loop (767DKE769) connecting ?15 and ?16 (cis-loop) within HCN in LC translocation; aliphatic substitution inhibited LC translocation but not other toxin functions such as cell binding, intracellular trafficking, or HCN-mediated pore formation. K768 was conserved among the CNTs. In molecular simulations of the HCN with a membrane, the cis-loop did not bind with the cell membrane. Taken together, the results of these studies implicate the cis-loop in LC translocation, independently of pore formation.IMPORTANCE How protein toxins translocate their catalytic domain across a cell membrane is the least understood step in toxin action. This study utilized a reporter, ?-lactamase, that was genetically fused to full-length, nontoxic tetanus toxin (?lac-TT) in discovery-based live-cell assays to study LC translocation. Directed mutagenesis identified a role for K768 in LC translocation. K768 was located between ?15 and ?16 (termed the cis-loop). Cellular assays showed that K768 did not interfere with other toxin functions, including cell binding, intracellular trafficking, and pore formation. The equivalent K768 is conserved among the clostridial neurotoxin family of proteins as a conserved structural motif. The cis-loop appears to contribute to LC translocation.

Dataset Information

Tetanus toxin is internalized by a sequential clathrin-dependent mechanism initiated within lipid microdomains and independent of epsin1.

Publications

Tetanus toxin is internalized by a sequential clathrin-dependent mechanism initiated within lipid microdomains and independent of epsin1.

Similar Datasets

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