The Respiratory Terminal Oxidases of Cyanobacteria

ALL CYANOBACTERIA CONTAIN AN AEROBIC RESPIRATORY CHAIN

Key enzymes of respiration: Respiratory Terminal Oxidases (RTOs) O e H +  2 H 2 O

Cyanobacterial RTOs: 3 protein families 3) Cyanide-insensitive quinol oxidases, homologues of plastid oxidase Ptox 2)Quinol oxidases (Qox), homologues of cytochrome bd from E. coli 1)Heme-Cu oxidases and relatives

At least five different enzymes of group 1 exist in cyanobacteria: a) Mitochondrial-type cytochrome c oxidases. Electron donor: cytochrome c. invariably 3 subunits with genes always arranged in the order coxBAC encoding subunits II, I, and III, respectively (Cox) b) Cytochrome cbb 3. Rare in cyanobacteria. In Synechococcus sp. PCC7942 the enzyme is a genuine cytochrome c oxidase despite having only 2 of the 8 subunits known from purple bacteria c) Three different types of ARTO (Alternate Respiratory Terminal Oxidases)

Definition of ARTO: 1)Three subunits with marked sequence similarity to the corresponding three subunits of cyanobacterial cytochrome c oxidase. 2) In most cases (but not always: an exception exists in Synechocystis sp. strain PCC6803) the gene arrangement is BAC, as with genuine cytochrome c oxidases 3) At least one of the two following marker- sequences of genuine cytochrome c oxidase is NOT present:

Subunit I: Mg 2+ binding site essential for transmembrane translocation of H+ Cytochrome c oxidase (Cox) WAHHMF ARTO (mostly, but not universally) WVHHMF Subunit II: Cu 2+ binding site essential for transfer of electrons from cytochrome c Cytochrome c oxidase(Cox) CaElCgpyHgvM ARTO DsqfSGaYfatm

ARTO type1: Subunit I: ARTO sequence Subunit II: ARTO sequence ARTO type2: Subunit I: ARTO sequence Subunit II: Cox sequence ARTO type3: Subunit I: Cox sequence Subunit II: ARTO sequence Electron donors for ARTO are not known

STRAIN Cox cbb3 ARTOtype1 ARTOtype2 ARTOtype3 Qox Ptox Nostoc (Anabaena) sp. PCC Anabaena variabilis ATCC Nostoc punctiforme PCC Trichodesmium erythraeum IMS Synechococcus sp. PCC Synechococcus sp. PCC Synechococcus sp. CC Synechococcus sp. CC Synechococcus sp. CC Synechococcus sp.JA-3-3Ab Synechococcus sp.JA-2-3B’a(2-13) Synechococcus sp. WH Synechococcus sp. RCC Synechococcus sp. PCC Synechocystis sp. PCC Thermosynechococcus elongatus BP Microcystis aeruginosa NIES Crocosphaera watsonii WH Cyanothece sp. PCC (?) 0 Cyanothece sp. PCC Cyanothece sp. ATCC Acaryochloris marina MBIC Gloeobacter violaceus PCC Prochlorococcus marinus SS Prochlorococcus marinus MED Prochlorococcus marinus MIT Prochlorococcus marinus MIT Prochlorococcus marinus MIT Prochlorococcus marinus MIT Prochlorococcus marinus MIT Prochlorococcus marinus NATL1A Prochlorococcus marinus NATL2A Prochlorococcus marinus AS

1. All cyanobacteria contain at least 1 RTO 2. No RTO is present in all cyanobacteria 3. The set of RTOs present in a cyanbacterium varies widely from strain to strain, even among closely related strains

Postulate In every cyanobacterium that contains more than 1 RTO, each RTO must have a specific function

Example Synechocystis sp. PCC6803 ________________________________________________________________________________________________________________________________ 1. Cox: essential for heterotrophic growth 2. ARTO: energization of the CM 3. Quinol oxidase (bd-type): valve for dissipation of surplus electrons in Q-pool

Bioenergetic pathways in Synechocystis 6803 DBMIB

Bioenergetic electron transport is a complex regulon with one set of substances, the quinone pool being the sole common component of all pathways