Metal-ion affinity and specificity in EF-hand proteins: coordination geometry and domain plasticity in parvalbumin

Structure. 1999 Oct 15;7(10):1269-78. doi: 10.1016/s0969-2126(00)80060-x.


Background: The EF-hand family is a large set of Ca(2+)-binding proteins that contain characteristic helix-loop-helix binding motifs that are highly conserved in sequence. Members of this family include parvalbumin and many prominent regulatory proteins such as calmodulin and troponin C. EF-hand proteins are involved in a variety of physiological processes including cell-cycle regulation, second messenger production, muscle contraction, microtubule organization and vision.

Results: We have determined the structures of parvalbumin mutants designed to explore the role of the last coordinating residue of the Ca(2+)-binding loop. An E101D substitution has been made in the parvalbumin EF site. The substitution decreases the Ca(2+)-binding affinity 100-fold and increases the Mg(2+)-binding affinity 10-fold. Both the Ca(2+)- and Mg(2+)-bound structures have been determined, and a structural basis has been proposed for the metal-ion-binding properties.

Conclusions: The E101D mutation does not affect the Mg(2+) coordination geometry of the binding loop, but it does pull the F helix 1.1 A towards the loop. The E101D-Ca(2+) structure reveals that this mutant cannot obtain the sevenfold coordination preferred by Ca(2+), presumably because of strain limits imposed by tertiary structure. Analysis of these results relative to previously reported structural information supports a model wherein the characteristics of the last coordinating residue and the plasticity of the Ca(2+)-binding loop delimit the allowable geometries for the coordinating sphere.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Binding Sites
  • Crystallography, X-Ray
  • EF Hand Motifs*
  • Humans
  • Models, Molecular
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Parvalbumins / chemistry*
  • Parvalbumins / genetics
  • Protein Conformation
  • Protein Structure, Tertiary


  • Parvalbumins

Associated data

  • PDB/1B8C
  • PDB/1B8L
  • PDB/1B8R
  • PDB/1B9A