1sdx

From Proteopedia

Revision as of 17:05, 2 February 2008

Crystal structure of the zinc saturated C-terminal half of bovine lactoferrin at 2.0 A resolution reveals two additional zinc binding sites

Overview

The crystal structure of the zinc-saturated C-terminal lobe of bovine, lactoferrin has been determined at 2.0 A resolution using crystals, stabilized at pH 3.8. This is the first metal-saturated structure of any, functional lactoferrin at such a low pH. Purified samples of, proteolytically generated zinc-saturated C-terminal lobe were crystallized, from 0.1 M MES buffer pH 6.5 containing 25%(v/v) polyethyleneglycol, monomethyl ether 550 and 0.1 M zinc sulfate heptahydrate. The crystals, were transferred to 25 mM ammonium acetate buffer containing 25%(v/v), polyethyleneglycol monomethyl ether 550 and the pH was gradually changed, from 6.5 to 3.8. The X-ray intensity data were collected with a 345 mm, imaging-plate scanner mounted on an RU-300 rotating-anode X-ray generator, using crystals soaked in the buffer at pH 3.8. The structure was, determined with the molecular-replacement method using the coordinates of, the monoferric C-terminal lobe of bovine lactoferrin as a search model and, was refined to an R factor of 0.192 for all data to 2.0 A resolution. The, final model comprises 2593 protein atoms (residues 342-676 and 681-685), 138 carbohydrate atoms (from 11 monosaccharide units in three glycan, chains), three Zn2+ ions, one CO3(2-) ion, one SO(4)2- ions and 227 water, molecules. The overall folding of the present structure is essentially, similar to that of the monoferric C-terminal lobe of bovine lactoferrin, although it contains Zn2+ in place of Fe3+ in the metal-binding cleft as, well as two additional Zn2+ ions on the surface of the C-terminal lobe., The Zn2+ ion in the cleft remains bound to the lobe with octahedral, coordination. The bidentate carbonate ion is stabilized by a network of, hydrogen bonds to Ala465, Gly466, Thr459 and Arg463. The other two zinc, ions also form sixfold coordinations involving symmetry-related protein, and water molecules. The number of monosaccharide residues from the three, glycan chains of the C-terminal lobe was 11, which is the largest number, observed to date. The structure shows that the C-terminal lobe of, lactoferrin is capable of sequestering a Zn2+ ion at a pH of 3.8. This, implies that the zinc ions can be sequestered over a wide pH range. The, glycan chain attached to Asn545 may also have some influence on iron, release from the C-terminal lobe.

About this Structure

1SDX is a Protein complex structure of sequences from Bos taurus with , and as ligands. Full crystallographic information is available from OCA.

Reference

Structure of the zinc-saturated C-terminal lobe of bovine lactoferrin at 2.0 A resolution., Jabeen T, Sharma S, Singh N, Bhushan A, Singh TP, Acta Crystallogr D Biol Crystallogr. 2005 Aug;61(Pt 8):1107-15. Epub 2005, Jul 20. PMID:16041076

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