1QX2: X-Ray Structure Of Calcium-Loaded Calbindomodulin (A Calbindin D9k Re- Engineered To Undergo A Conformational Opening) At 1.44 A Resolution

The extent of conformational change that calcium binding induces in EF-hand proteins is a key biochemical property specifying Ca(2+) sensor versus signal modulator function. To understand how differences in amino acid sequence lead to differences in the response to Ca(2+) binding, comparative analyses of sequence and structures, combined with model building, were used to develop hypotheses about which amino acid residues control Ca(2+)-induced conformational changes. These results were used to generate a first design of calbindomodulin (CBM-1), a calbindin D(9k) re-engineered with 15 mutations to respond to Ca(2+) binding with a conformational change similar to that of calmodulin. The gene for CBM-1 was synthesized, and the protein was expressed and purified. Remarkably, this protein did not exhibit any non-native-like molten globule properties despite the large number of mutations and the nonconservative nature of some of them. Ca(2+)-induced changes in CD intensity and in the binding of the hydrophobic probe, ANS, implied that CBM-1 does undergo Ca(2+) sensorlike conformational changes. The X-ray crystal structure of Ca(2+)-CBM-1 determined at 1.44 A resolution reveals the anticipated increase in hydrophobic surface area relative to the wild-type protein. A nascent calmodulin-like hydrophobic docking surface was also found, though it is occluded by the inter-EF-hand loop. The results from this first calbindomodulin design are discussed in terms of progress toward understanding the relationships between amino acid sequence, protein structure, and protein function for EF-hand CaBPs, as well as the additional mutations for the next CBM design.
PDB ID: 1QX2Download
MMDB ID: 27684
PDB Deposition Date: 2003/9/4
Updated in MMDB: 2012/12
Experimental Method:
x-ray diffraction
Resolution: 1.44  Å
Source Organism:
Similar Structures:
Biological Unit for 1QX2: monomeric; determined by author and by software (PQS)
Molecular Components in 1QX2
Label Count Molecule
Protein (1 molecule)
Vitamin D-dependent Calcium-binding Protein, Intestinal(Gene symbol: S100G)
Molecule annotation
Chemicals (3 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB