illustrated by the discovery of EF-hand-like domains in bacterial proteins. For example, a helix-loop-strand instead of the helix-loop-helix structure is in periplasmic galactose-binding protein ( Salmonella typhimurium , PDB 1gcg ) or alginate-binding protein ( Sphingomonas sp., 1kwh ); the entering helix is missing in protective antigen ( Bacillus anthracis , 1acc