1oql

From Proteopedia

Revision as of 20:59, 20 November 2007

Mistletoe Lectin I from Viscum album complexed with galactose

Overview

The X-ray structure of mistletoe lectin I (MLI), a type-II, ribosome-inactivating protein (RIP), cocrystallized with galactose is, described. The model was refined at 3.0 A resolution to an R-factor of, 19.9% using 21 899 reflections, with Rfree 24.0%. MLI forms a homodimer, (A-B)2 in the crystal, as it does in solution at high concentration. The, dimer is formed through contacts between the N-terminal domains of two, B-chains involving weak polar and non-polar interactions. Consequently, the overall arrangement of sugar-binding sites in MLI differs from those, in monomeric type-II RIPs: two N-terminal sugar-binding sites are 15 A, apart on one side of the dimer, and two C-terminal sugar-binding sites are, 87 A apart on the other side. Galactose binding is achieved by common, hydrogen bonds for the two binding sites via hydroxy groups 3-OH and 4-OH, and hydrophobic contact by an aromatic ring. In addition, at the, N-terminal site 2-OH forms hydrogen bonds with Asp27 and Lys41, and at the, C-terminal site 3-OH and 6-OH undergo water-mediated interactions and C5, has a hydrophobic contact. MLI is a galactose-specific lectin and shows, little affinity for N-acetylgalactosamine. The reason for this is, discussed. Structural differences among the RIPs investigated in this, study (their quaternary structures, location of sugar-binding sites, and, fine sugar specificities of their B-chains, which could have diverged, through evolution from a two-domain protein) may affect the binding sites, and consequently the cellular transport processes and biological responses, of these toxins.

About this Structure

1OQL is a Protein complex structure of sequences from Viscum album with GAL and NAG as ligands. Active as rRNA N-glycosylase, with EC number 3.2.2.22 Full crystallographic information is available from OCA.

Reference

Crystal structure at 3 A of mistletoe lectin I, a dimeric type-II ribosome-inactivating protein, complexed with galactose., Niwa H, Tonevitsky AG, Agapov II, Saward S, Pfuller U, Palmer RA, Eur J Biochem. 2003 Jul;270(13):2739-49. PMID:12823544

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