Zinc/calcium- and cadmium/cadmium-substituted concanavalin A: interplay of metal binding, pH and molecular packing.

TitleZinc/calcium- and cadmium/cadmium-substituted concanavalin A: interplay of metal binding, pH and molecular packing.
Publication TypeJournal Article
Year of Publication2000
AuthorsBouckaert, J., R. Loris, and L. Wyns
JournalActa Crystallogr D Biol Crystallogr
Volume56
IssuePt 12
Pagination1569-76
Date Published2000 Dec
ISSN0907-4449
KeywordsAspartic Acid, Binding Sites, Cadmium, Calcium, Concanavalin A, Fabaceae, Histamine, Hydrogen-Ion Concentration, Models, Molecular, Plant Lectins, Plants, Medicinal, Protein Conformation, X-Ray Diffraction, Zinc
Abstract

The crystal structures of cadmium/cadmium and zinc/calcium concanavalin A (con A) at pH 5.0 and pH 6.15, respectively, were determined. The structure of cadmium/cadmium con A confirms that the secondary Cd(2+)-binding site S3 is empty at pH 5. The metal-binding sites S1 and S2 are only very slightly affected by the substitution with cadmium. On the other hand, S1 and S2 and most of the protein surface of zinc/calcium con A at pH 6.15 differ from other fully metal-bound and carbohydrate-free structures. Most of these structural differences at the protein surface are a result of the interplay between metal binding, protonation and crystal packing. This interplay is expressed by relative rotations and translations of the con A units in alternative crystal packings and participation in space-group conversions inside crystals in situ. The particular crystal packing of zinc/calcium con A creates a novel zinc-binding site S4. The Zn(2+) ion in S4 ligates two aspartates from one tetramer and a histidine from a symmetry-related tetramer.

Alternate JournalActa Crystallogr. D Biol. Crystallogr.
PubMed ID11092923