5.B.5.1.3
Extracellular respiratory system with 3 cytochrome protein components, a periplasmic protein, MtrD, of 321 aas, a porin-type protein, MtrE, of 712 aas, and a surface decaheme cytochrome c component, MtrF, of 639 aas.  Each protein has a single N-terminal targeting TMS. They function together in the reduction of extracellular iron and manganese oxides (Barrozo et al. 2018) using a cytoplasmic electron donor. These 3 proteins are parologous to MtrABC (TC# 5.B.5.1.1) and function in parallel, except that in contrast to MtrABC, no increase in mtrDEF gene expression is observed under O₂‐limited conditions (Barchinger et al. 2016). This process is being exploited for the generation of renewable energy technologies incorporating microbial catalysts on electrode surfaces for fuel‐to‐electricity (microbial fuel cells) or electricity‐to‐fuel (microbial electrosynthesis) conversion (Rabaey and Rozendal 2010; Santoro et al. 2017).