Biological metal-tetrapyrrole complexes, such as heme, cobalamin, and cofactor F430, play critical roles in life. These metal complexes are built up in the corresponding biosynthetic machineries consisting in various types of enzymes. In the machineries, chelatases are responsible for insertion of a divalent metal ion to a macrocyclic tetrapyrrole. The chelatases are categorized into three distinct classes (class I, II and III), based on their structural and functional features. Among them, the class II chelatase family has long been studied for understanding the metal-insertion mechanism. Recently, class II nickel-chelatase CfbA derived from cofactor F430-utilizing archaea has been characterized to have unique features as an "ancestral" class II chelatase distinct from typical class II cobalt- and ferro-chelatases. Toward an understanding of diversity and molecular evolution of class II chelatases, we have performed structural and functional analyses of CfbA and its variants or homologues[1-3].