2cb6
From Proteopedia
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CRYSTAL STRUCTURE OF THE CATALYTIC DOMAIN OF THE MOSQUITOCIDAL TOXIN FROM BACILLUS SPHAERICUS, MUTANT E195Q
Overview
The catalytic domain of a mosquitocidal toxin prolonged by a C-terminal 44, residue linker connecting to four ricin B-like domains was crystallized., Three crystal structures were established at resolutions between 2.5A and, 3.0A using multi-wavelength and single-wavelength anomalous X-ray, diffraction as well as molecular replacement phasing techniques. The, chainfold of the toxin fragment corresponds to those of ADP-ribosylating, enzymes. At pH 4.3 the fragment is associated in a C(7)-symmetric heptamer, in agreement with an aggregate of similar size observed by size-exclusion, chromatography. In two distinct crystal forms, the heptamers formed nearly, spherical, D(7)-symmetric tetradecamers. Another crystal form obtained at, pH 6.3 contained a recurring C(2)-symmetric tetramer, which, however, was, not stable in solution. On the basis of the common chainfold and, NAD(+)-binding site of all ADP-ribosyl transferases, the NAD(+)-binding, site of the toxin was assigned at a high confidence level. In all three, crystal forms the NAD(+) site was occupied by part of the 44 residue, linker, explaining the known inhibitory effect of this polypeptide region., The structure showed that the cleavage site for toxin activation is in a, highly mobile loop that is exposed in the monomer. Since it contains the, inhibitory linker as a crucial part of the association contact, the, observed heptamer is inactive. Moreover, the heptamer cannot be activated, by proteolysis because the activation loop is at the ring center and not, accessible for proteases. Therefore the heptamer, or possibly the, tetradecamer, seems to represent an inactive storage form of the toxin.
About this Structure
2CB6 is a Single protein structure of sequence from Lysinibacillus sphaericus. Full crystallographic information is available from OCA.
Reference
Structure of the mosquitocidal toxin from Bacillus sphaericus., Reinert DJ, Carpusca I, Aktories K, Schulz GE, J Mol Biol. 2006 Apr 7;357(4):1226-36. Epub 2006 Jan 27. PMID:16483607
Page seeded by OCA on Tue Jan 29 18:39:53 2008
