Binding of calcium in the EF-hand of Escherichia coli lytic transglycosylase Slt35 is important for stability

The Escherichia coli lytic transglycosylase Slt35 contains a single metal i on-binding site that resembles EF-hand calcium-binding sites. The Slt35 EF- hand is only the second observation of such a domain in a prokaryotic prote in. Two crystal structures at 2.1;Angstrom resolution show that both Ca2+ i ons and Na+ ions can bind to the EF-hand domain, but in subtly different co nfigurations. Heat-induced unfolding studies demonstrate that Ca2+ ions are preferentially bound, and that only Ca2+ ions significantly increase the m elting temperature of Slt35. This shows that the EF-hand calcium-binding do main is important for the stability of Slt35. (C) 1999 Federation of Europe an Biochemical Societies.