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Sequential structural changes upon zinc and calcium binding to metal-free concanavalin A
J Bouckaert1, F Poortmans, L Wyns
1Laboratorium voor Ultrastructuur, Vlaams Interuniversitair Instituut voor Biotechnologie, Vrije Universiteit Brussel and Vlaamse Instelling voor Technologisch Onderzoek, Boeretang 200, B-2400 Mol, Belgium.
The Journal of Biological Chemistry
|July 5, 1996
Summary
Concanavalin A (ConA) requires sequential metal ion binding for saccharide recognition. Zinc binding in site S1 is crucial for enabling subsequent calcium binding in site S2, forming the active holoprotein.
Area of Science:
- Biochemistry
- Structural Biology
- Protein Crystallography
Background:
- Concanavalin A (ConA) is a lectin that requires sequential binding of metal ions to form its functional saccharide-binding site.
- The process involves binding a transition metal ion in site S1 and a calcium ion in site S2.
Purpose of the Study:
- To elucidate the structural and sequential metal-binding mechanism of ConA.
- To understand the role of metal ions in ConA's conformational changes and saccharide-binding site formation.
Main Methods:
- X-ray crystallography of metal-free ConA co-crystallized with various metal ions (Zn2+, Co2+, Ca2+).
- Analysis of apo-ConA, monometallized ConA (apoZn-ConA, apoCo-ConA), and fully metallized ConA (ConA ZnCa).
Main Results:
- Metal-free ConA crystals soaked with Zn2+ or Co2+ showed partial metal binding without significant conformational changes.
- Zn2+ fully occupied the S1 site in Zn-ConA, influencing Asp10 and Asp19 positions, which is essential for subsequent Ca2+ binding.
- Ca2+ binding in the S2 site of ConA ZnCa induced large conformational changes, including peptide bond isomerization, forming the saccharide-binding site.
- Zn2+ ligation in ConA ZnCa was similar to other divalent metal ions (Mn2+, Cd2+, Co2+, Ni2+), contradicting previous EXAFS data.
Conclusions:
- The binding of Zn2+ in the S1 site is a prerequisite for Ca2+ binding in the S2 site, enabling the formation of the active ConA holoprotein.
- The sequential metal binding and associated conformational changes are critical for ConA's biological function in saccharide recognition.