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Structure–Function Relationships of the Repeat Domains of RTX Toxins

Institute of Biochemistry, University of Cologne, Zülpicherstrasse 47, D-50674 Cologne, Germany
Toxins 2019, 11(11), 657; https://doi.org/10.3390/toxins11110657
Received: 21 October 2019 / Revised: 7 November 2019 / Accepted: 9 November 2019 / Published: 12 November 2019
(This article belongs to the Special Issue RTX Toxins)
RTX proteins are a large family of polypeptides of mainly Gram-negative origin that are secreted into the extracellular medium by a type I secretion system featuring a non-cleavable C-terminal secretion signal, which is preceded by a variable number of nine-residue tandem repeats. The three-dimensional structure forms a parallel β-roll, where β-strands of two parallel sheets are connected by calcium-binding linkers in such a way that a right-handed spiral is built. The Ca2+ ions are an integral part of the structure, which cannot form without them. The structural determinants of this unique architecture will be reviewed with its conservations and variations together with the implication for secretion and folding of these proteins. The general purpose of the RTX domains appears to act as an internal chaperone that keeps the polypeptide unfolded in the calcium-deprived cytosol and triggers folding in the calcium-rich extracellular medium. A rather recent addition to the structural biology of the RTX toxin is a variant occurring in a large RTX adhesin, where this non-canonical β-roll binds to ice and diatoms. View Full-Text
Keywords: RTX toxin; type I secretion; calcium; internal chaperone; protein folding; tertiary structure RTX toxin; type I secretion; calcium; internal chaperone; protein folding; tertiary structure
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Baumann, U. Structure–Function Relationships of the Repeat Domains of RTX Toxins. Toxins 2019, 11, 657.

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