The second Ca 2+ -binding domain of the Na + –Ca 2+ exchanger is essential for regulation: Crystal structures and mutational analysis

• DOI: 10.1073/pnas.0707417104
• Publication Date: 2007-10-25T23:36:11Z
• Authors: Gabriel Mercado B...; Michela Ottolia; Debora A. Nicoll; Vincent Chaptal; Duilio Cascio; Kenneth D. Philipson; Jeff Abramson
• Keywords: Crystal (programming language)

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