1enr
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CO-CRYSTALS OF DEMETALLIZED CONCANAVALIN A WITH ZINC AND CALCIUM HAVING A ZINC ION BOUND IN THE S1 SITE AND A CALCIUM ION BOUND IN THE S2 SITE
OverviewOverview
The lectin concanavalin A (ConA) sequentially binds a transition metal ion, in the metal-binding site S1 and a calcium ion in the metal-binding site, S2 to form its saccharide-binding site. Metal-free ConA crystals soaked, with either Zn2+ (apoZn-ConA) or Co2+ (apoCo-ConA) display partial binding, of these ions in the proto-transition metal-binding site, but no further, conformational changes are observed. These structures can represent the, very first step in going from metal-free ConA toward the holoprotein. In, the co-crystals of metal-free ConA with Zn2+ (Zn-ConA), the zinc ion can, fully occupy the S1 site. The positions of the carboxylate ligands Asp10, and Asp19 that bridge the S1 and S2 sites are affected. The ligation to, Zn2+ orients Asp10 optimally for calcium ligation and stabilizes Asp19 by, a hydrogen bond to one of its water ligands. The neutralizing and, stabilizing effect of the binding of Zn2+ in S1 is necessary to allow for, subsequent Ca2+ binding in the S2 site. However, the S2 site of, monometallized ConA is still disrupted. The co-crystals of metal-free ConA, with both Zn2+ and Ca2+ contain the active holoprotein (ConA ZnCa). Ca2+, has induced large conformational changes to stabilize its, hepta-coordination in the S2 site, which comprise the trans to cis, isomerization of the Ala207-Asp208 peptide bond accompanied by the, formation of the saccharide-binding site. The Zn2+ ligation in ConA ZnCa, is similar to Mn2+, Cd2+, Co2+, or Ni2+ ligation in the S1 site, in, disagreement with earlier extended x-ray absorption fine structure results, that suggested a lower coordination number for Zn2+.
About this StructureAbout this Structure
1ENR is a Single protein structure of sequence from Canavalia ensiformis with CA and ZN as ligands. Full crystallographic information is available from OCA.
ReferenceReference
Sequential structural changes upon zinc and calcium binding to metal-free concanavalin A., Bouckaert J, Poortmans F, Wyns L, Loris R, J Biol Chem. 1996 Jul 5;271(27):16144-50. PMID:8663112
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