3.A.28. The AAA-ATPase, Bcs1 (Bcs1) Family
The mitochondrial AAA-ATPase, Bcs1, mediates topogenesis of the Rieske protein, Rip1, a component of respiratory chains in bacteria, mitochondria, and chloroplasts (Wagener et al. 2011). The oligomeric AAA-ATPase, Bcs1, is involved in export of the folded Fe-S domain of Rip1 across the inner membrane and insertion of its transmembrane segment into an assembly intermediate of the cytochrome bc1 complex. Structural elements in Rip1 are required for recognition and export by as well as ATP-dependent lateral release from the AAA-ATPase. In bacteria and chloroplasts, Rip1 uses the Tat machinery for topogenesis; however, mitochondria have lost this machinery during evolution, and a member of the AAA-ATPase family has taken over its function (Wagener et al., 2011). Mutations in Bcs1 lead to different properties of the protein and different disease-related symptoms (Wagener and Neupert 2012). A conserved α-helix in Bcs1 is required for Respiratory Complex III maturation (Sawamura et al. 2014). Human BCS1 has been implicated in human mitochondrial disorders (e.g. Björnstad and Gracile syndromes) (Ostojić et al. 2014). The outer membrane AAA-ATPase of Arabidopsis thaliana, AtOM66, affects cell death and pathogen resistance (Zhang et al. 2014).