The Monoheme c Subunit of Respiratory Alternative Complex III Is Not Essential for Electron Transfer to Cytochrome aa ₃ in Flavobacterium johnsoniae

Abstract

Energy conversion is a fundamental process of all organisms, realized by specialized protein complexes, one of which is alternative complex III (ACIII). ACIII is a functional analogue of well-known mitochondrial complex III, but operates according to a different, still unknown mechanism.

A cytochrome c551 mediates the cyclic electron transport chain of the anoxygenic phototrophic bacterium Roseiflexus castenholzii

“…johnsoniae ACIII, which possesses six c -type hemes in the ActA subunit, both rc ACIII and R . marinus ACIII lacked the ActA N-terminal mobile domain that contains the sixth c -type heme ( Lorencik et al., 2021 ). As a result, the monoheme in the ActE subunit of rc ACIII (or R .…”

“…However, rc ACIII-mediated electron transfer back to the rc RC to form a cyclic ETC has not been experimentally verified. Moreover, although Ac is the only known downstream electron acceptor of FAP ACIIIs ( Gao et al., 2009 ; Majumder et al., 2013 ), respiratory ACIIIs often have alternative ultimate electron acceptors and branched electron transfer routes ( Refojo et al., 2010a ; Sousa et al., 2018 ; Sun et al., 2018 ; Lorencik et al., 2021 ). It is therefore difficult to exclude the existence of other periplasmic electron acceptors in cyclic ETC.…”