P1B-ATPases -: an ancient family of transition metal pumps with diverse functions in plants

P-1B-ATPases form a distinct evolutionary sub-family of P-type ATPases, transporting transition metals such as Cu, Zn, Cd, Pb and Co across membranes in a wide range of organisms, including plants. Structurally they are distinct from other P-types, possessing eight transmembrane helices, a CPx/SPC motif in transmembrane domain six, and putative transition metal-binding domains at the N- and/or C-termini. Arabidopsis has eight P-1B-ATPases (AtHMA1-AtHMA8), which differ in their structure, function and regulation. They perform a variety of important physiological tasks relating to transition metal transport and homeostasis. The crucial roles of plant P-1B-ATPases in micronutrient nutrition, delivery of essential metals to target proteins, and toxic metal detoxification are discussed.