Structural studies of metal-binding proteins revealing dynamic behaviour

Research output: ThesisDoctoral Thesis (compilation)

Abstract

The Mg<sup>2+</sup> and Mn<sup>2+</sup> structures of calbindin D<sub>9k</sub> have been determined and they reveal a conformational change compared to the structures of apo and (Ca<sup>2+</sup>)2-calbindin D<sub>9k</sub>. These findings are unique, since normally calcium and not magnesium is known to induce conformational changes of EF-hand proteins. It has also been shown that calbindin D<sub>9k</sub> binds one Mg<sup>2+</sup> (K<sub>d</sub>=1mM) in the regular C-terminal EF-hand close to physiological conditions. The binding of Mg<sup>2+</sup> decreases the affinity for Ca<sup>2+</sup>, 5-fold and vice versa.

Two apo staphylococcal enterotoxin H (SEH) structures and one ZnSEH structure have been determined. The structures reveal that SEH lacks the SEB-like binding to MHC class II. Based upon structural differences for the same protein a novel mechanism for SEH recognition of different TcR Vbeta is suggested. The ZnSEH structure together with the homodimers of SEH formed by the crystal packing in two crystal forms imply the approximate area used for Zn<sup>2+</sup>-dependent binding to MHC class II.

A dimeric form of calbindin D<sub>9k</sub> has been found. The C-terminal EF-hand of one monomer packs towards the N-terminal EF-hand of the other monomer and vice versa. The dimerisation is primarily caused by the P43M substitution in the linker region between the EF-hands and low pH (= 5.0). The P43M substitution may facilitate 3D domain swapping in two ways; by inducing an extended hydrophobic core in the dimeric form of calbindin D<sub>9k</sub> and by stabilizing a partially unfolded form of calbindin D<sub>9k</sub> .

The structure of staphylococcal enterotoxin A (SEA) with the substitution H187A (SEA<sub>H187A</sub>) has been determined. SEA<sub>H187A</sub> has previously been shown to give rise to reduced affinity for Zn<sup>2+</sup> and a 10-fold decrease in Zn<sup>2+</sup>-dependent binding to MHC class II. The structure and aggregation analyses reveal the importance of additional ligands for SEA<sub>H187A</sub> to bind Zn<sup>2+</sup> at low physiological Zn<sup>2+</sup> concentrations.

Details

Authors
  • Maria Håkansson
Organisations
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Biological Sciences

Keywords

  • Kemi, Chemistry, Molekylär biofysik, Molecular biophysics, zinc, magnesium, superantigen, calbindin D9k, X-ray crystallography, staphylococcal enterotoxin, structure, Chemical technology and engineering, Kemiteknik och kemisk teknologi
Original languageEnglish
QualificationDoctor
Awarding Institution
Supervisors/Assistant supervisor
  • [unknown], [unknown], Supervisor, External person
Award date2001 May 4
Publisher
  • Molecular Biophysics, Lund University
Publication statusPublished - 2001
Publication categoryResearch

Bibliographic note

Defence details Date: 2001-05-04 Time: 14:00 Place: K:A at the Center of Chemistry and Chemical Engineering External reviewer(s) Name: Jones, E Yvonne Title: [unknown] Affiliation: Cambridge ---