Title

The pertussis toxin S1 subunit is a thermally unstable protein susceptible to degradation by the 20S proteasome

Authors

Authors

A. H. Pande; D. Moe; M. Jamnadas; S. A. Tatulian;K. Teter

Comments

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Abbreviated Journal Title

Biochemistry

Keywords

RICIN-A-CHAIN; ENDOPLASMIC-RETICULUM; CHOLERA-TOXIN; ADP-RIBOSYLATION; EUKARYOTIC CELLS; INTRACELLULAR TRAFFICKING; SELECTIVE DEGRADATION; RETROGRADE TRANSPORT; ADENINE-NUCLEOTIDES; OXIDIZED CALMODULIN; Biochemistry & Molecular Biology

Abstract

Pertussis toxin ( PT) is an AB-type protein toxin that consists of a catalytic A subunit ( PT S1) and an oligomeric, cell-binding B subunit. It belongs to a subset of AB toxins that move from the cell surface to the endoplasmic reticulum ( ER) before the A chain passes into the cytosol. Toxin translocation is thought to involve A chain unfolding in the ER and the quality control mechanism of ER-associated degradation ( ERAD). The absence of lysine residues in PT S1 may allow the translocated toxin to avoid ubiquitin-dependent degradation by the 26S proteasome, which is the usual fate of exported ERAD substrates. As the conformation of PT S1 appears to play an important role in toxin translocation, we used biophysical and biochemical methods to examine the structural properties of PT S1. Our in vitro studies found that the isolated PT S1 subunit is a thermally unstable protein that can be degraded in a ubiquitin-independent fashion by the core 20S proteasome. The thermal denaturation of PT S1 was inhibited by its interaction with NAD, a donor molecule used by PT S1 for the ADP ribosylation of target G proteins. These observations support a model of intoxication in which toxin translocation, degradation, and activity are all influenced by the heat-labile nature of the isolated toxin A chain.

Journal Title

Biochemistry

Volume

45

Issue/Number

46

Publication Date

1-1-2006

Document Type

Article

Language

English

First Page

13734

Last Page

13740

WOS Identifier

WOS:000242021100006

ISSN

0006-2960

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