2QVK

The second Ca2+-binding domain of the Na+-Ca2+ exchanger is essential for regulation: crystal structures and mutational analysis

Summary for 2QVK

• Entry DOI: 10.2210/pdb2qvk/pdb
• Related: 2DPK 2FWU 2QVM
• Descriptor: Sodium/calcium exchanger 1 (2 entities in total)
• Functional Keywords: cbd2, calcium binding domain, sodium calcium exchanger, metal binding protein
• Biological source: Canis lupus familiaris (dog)
• Cellular location: Cell membrane; Multi-pass membrane protein: P23685
• Total number of polymer chains: 1
• Total formula weight: 21648.38

Authors

Chaptal, V.,Mercado Besserer, G.,Abramson, J.,Cascio, D. (deposition date: 2007-08-08, release date: 2007-11-13, Last modification date: 2024-02-21)

Primary citation

Mercado Besserer, G.,Ottolia, M.,Nicoll, D.A.,Chaptal, V.,Cascio, D.,Philipson, K.D.,Abramson, J.
The second Ca2+-binding domain of the Na+ Ca2+ exchanger is essential for regulation: crystal structures and mutational analysis
Proc.Natl.Acad.Sci.Usa, 104:18467-18472, 2007

PubMed Abstract: The Na(+)-Ca(2+) exchanger plays a central role in cardiac contractility by maintaining Ca(2+) homeostasis. Two Ca(2+)-binding domains, CBD1 and CBD2, located in a large intracellular loop, regulate activity of the exchanger. Ca(2+) binding to these regulatory domains activates the transport of Ca(2+) across the plasma membrane. Previously, we solved the structure of CBD1, revealing four Ca(2+) ions arranged in a tight planar cluster. Here, we present structures of CBD2 in the Ca(2+)-bound (1.7-A resolution) and -free (1.4-A resolution) conformations. Like CBD1, CBD2 has a classical Ig fold but coordinates only two Ca(2+) ions in primary and secondary Ca(2+) sites. In the absence of Ca(2+), Lys(585) stabilizes the structure by coordinating two acidic residues (Asp(552) and Glu(648)), one from each of the Ca(2+)-binding sites, and prevents a substantial protein unfolding. We have mutated all of the acidic residues that coordinate the Ca(2+) ions and have examined the effects of these mutations on regulation of exchange activity. Three mutations (E516L, D578V, and E648L) at the primary Ca(2+) site completely remove Ca(2+) regulation, placing the exchanger into a constitutively active state. These are the first data defining the role of CBD2 as a regulatory domain in the Na(+)-Ca(2+) exchanger.

PubMed: 17962412
DOI: 10.1073/pnas.0707417104

Experimental method

X-RAY DIFFRACTION (1.451 Å)