1KTW

IOTA-CARRAGEENASE COMPLEXED TO IOTA-CARRAGEENAN FRAGMENTS

Summary for 1KTW

• Entry DOI: 10.2210/pdb1ktw/pdb
• Related: 1H80
• Descriptor: IOTA-CARRAGEENASE, 3,6-anhydro-2-O-sulfo-alpha-D-galactopyranose-(1-3)-4-O-sulfo-beta-D-galactopyranose, 3,6-anhydro-2-O-sulfo-alpha-D-galactopyranose-(1-3)-4-O-sulfo-beta-D-galactopyranose-(1-4)-3,6-anhydro-2-O-sulfo-alpha-D-galactopyranose-(1-3)-4-O-sulfo-beta-D-galactopyranose, ... (7 entities in total)
• Functional Keywords: hydrolase, iota-carrageenan double helix degradation
• Biological source: Alteromonas sp. ATCC 43554
• Total number of polymer chains: 2
• Total formula weight: 105871.02

Authors

Michel, G.,Kahn, R.,Dideberg, O. (deposition date: 2002-01-18, release date: 2003-06-10, Last modification date: 2024-11-20)

Primary citation

Michel, G.,Helbert, W.,Kahn, R.,Dideberg, O.,Kloareg, B.
The Structural Bases of the Processive Degradation of iota-Carrageenan, a Main Cell Wall Polysaccharide of Red Algae.
J.Mol.Biol., 334:421-433, 2003

PubMed Abstract: 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.

PubMed: 14623184
DOI: 10.1016/j.jmb.2003.09.056

Experimental method

X-RAY DIFFRACTION (2 Å)