Thermophilic P-loop transport ATPases: Enzyme function and energetics at high temperature

Primary transport ATPases are divided into several superfamilies; amongst others including ATPases of the ABC transporter superfamily, the F-ATPase superfamily or the motor ATPases of the General Secretory (Sec) pathway. Motor proteins from these superfamilies show a low sequence similarity, except for their nucleotide binding domains (NBDs) that are responsible for the binding of ATP molecule. The NBD domain of these ATPases contains many conserved amino acid sequence motifs, notably the most typical phosphate-loop (P-loop) sequence. Together with the other motifs, the P-loop participates in the formation of the catalytic site that allows hydrolysis of ATP. Therefore, these ATPases are often termed P-loop ATPases (1). Sequence homology and secondary structure analysis of these ATPases revealed the prototype of a typical NBD (2) termed the RecA or F1 fold. Proteins containing a RecA or F1 fold are often called RecA-like motor proteins. Here we will review RecA –like transport ATPases of extreme thermophilic bacteria and archaea in the aspect of their functional, structural and energetic characteristics. We are going to focus on the group of thermophilic RecA-like transport ATPases including ABC-type uptake systems, ion-translocating ATPases such as the F1F0 and A1A0 rotary motors, but also exporter systems like the SecA ATPase of the general protein secretion system (3-7).