1tii
From Proteopedia
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ESCHERICHIA COLI HEAT LABILE ENTEROTOXIN TYPE IIB
Overview
BACKGROUND: Cholera toxin from Vibrio cholerae and the type I heat-labile, enterotoxins (LT-Is) from Escherichia coli are oligomeric proteins with, AB5 structures. The type II heat-labile enterotoxins (LT-IIs) from E. coli, are structurally similar to, but antigenically distinct from, the type I, enterotoxins. The A subunits of type I and type II enterotoxins are, homologous and activate adenylate cyclase by ADP-ribosylation of a G, protein subunit, G8 alpha. However, the B subunits of type I and type II, enterotoxins differ dramatically in amino acid sequence and, ganglioside-binding specificity. The structure of LT-IIb was determined, both as a prototype for other LT-IIs and to provide additional insights, into structure/function relationships among members of the heat-labile, enterotoxin family and the superfamily of ADP-ribosylating protein toxins., RESULTS: The 2.25 A crystal structure of the LT-IIb holotoxin has been, determined. The structure reveals striking similarities with LT-I in both, the catalytic A subunit and the ganglioside-binding B subunits. The latter, form a pentamer which has a central pore with a diameter of 10-18 A., Despite their similarities, the relative orientation between the A, polypeptide and the B pentamer differs by 24 degrees in LT-I and LT-IIb. A, common hydrophobic ring was observed at the A-B5 interface which may be, important in the cholera toxin family for assembly of the AB5, heterohexamer. A cluster of arginine residues at the surface of the A, subunit of LT-I and cholera toxin, possibly involved in assembly, is also, present in LT-IIb. The ganglioside receptor binding sites are localized, as suggested by mutagenesis, and are in a position roughly similar to the, sites where LT-I binds its receptor. CONCLUSIONS: The structure of LT-IIb, provides insight into the sequence diversity and structural similarity of, the AB5 toxin family. New knowledge has been gained regarding the assembly, of AB5 toxins and their active-site architecture.
About this Structure
1TII is a Protein complex structure of sequences from Escherichia coli. Full crystallographic information is available from OCA.
Reference
Crystal structure of a new heat-labile enterotoxin, LT-IIb., van den Akker F, Sarfaty S, Twiddy EM, Connell TD, Holmes RK, Hol WG, Structure. 1996 Jun 15;4(6):665-78. PMID:8805549
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