1ktw
From Proteopedia
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IOTA-CARRAGEENASE COMPLEXED TO IOTA-CARRAGEENAN FRAGMENTS
Overview
iota-Carrageenans are sulfated 1,3-alpha-1,4-beta-galactans from the cell, walls of red algae, which auto-associate into crystalline fibers made of, aggregates of double-stranded helices. iota-Carrageenases, which, constitute family 82 of glycoside hydrolases, fold into a right-handed, beta-helix. Here, the structure of Alteromonas fortis iota-carrageenase, bound to iota-carrageenan fragments was solved at 2.0A resolution (PDB, 1KTW). The enzyme holds a iota-carrageenan tetrasaccharide (subsites +1 to, +4) and a disaccharide (subsites -3, -4), thus providing the first direct, determination of a 3D structure of iota-carrageenan. Electrostatic, interactions between basic protein residues and the sulfate substituents, of the polysaccharide chain dominate iota-carrageenan recognition. Glu245, and Asp247 are the proton donor and the base catalyst, respectively., C-terminal domain A, which was highly flexible in the native enzyme, structure, adopts a alpha/beta-fold, also found in DNA/RNA-binding, domains. In the substrate-enzyme complex, this polyanion-binding module, shifts toward the beta-helix groove, forming a tunnel. Thus, from an open, conformation which allows for the initial endo-attack of iota-carrageenan, chains, the enzyme switches to a closed-tunnel form, consistent with its, highly processive character, as seen from the electron-microscopy analysis, of the degradation of iota-carrageenan fibers.
About this Structure
1KTW is a Single protein structure of sequence from Alteromonas sp. atcc 43554 with CA, NA and CL as ligands. Active as Iota-carrageenase, with EC number 3.2.1.157 Full crystallographic information is available from OCA.
Reference
The structural bases of the processive degradation of iota-carrageenan, a main cell wall polysaccharide of red algae., Michel G, Helbert W, Kahn R, Dideberg O, Kloareg B, J Mol Biol. 2003 Nov 28;334(3):421-33. PMID:14623184
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