Abstract
Flavodiiron proteins (FDPs, also called flavoproteins, Flvs) are modular enzymes widely present in Bacteria and Archaea. The evolution of cyanobacteria and oxygenic photosynthesis occurred in concert with the modulation of typical bacterial FDPs. Present cyanobacterial FDPs are composed of three domains, the β-lactamase-like, flavodoxin-like and flavin-reductase like domains. Cyanobacterial FDPs function as hetero- and homodimers and are involved in the regulation of photosynthetic electron transport. Whilst Flv2 and Flv4 proteins are limited to specific cyanobacterial species (β-cyanobacteria) and function in photoprotection of Photosystem II, Flv1 and Flv3 proteins, functioning in the “Mehler-like” reaction and safeguarding Photosystem I under fluctuating light conditions, occur in nearly all cyanobacteria and additionally in green algae, mosses and lycophytes. Filamentous cyanobacteria have additional FDPs in heterocyst cells, ensuring a microaerobic environment for the function of the nitrogenase enzyme under the light. Here, the evolution, occurrence and functional mechanisms of various FDPs in oxygenic photosynthetic organisms are discussed.
Highlights
Flavodiiron proteins (FDPs), previously called A-type flavoproteins (Flv) [1], are a large family of enzymes sharing sequence similarity
The filamentous heterocystous cyanobacteria are marked with a gray background; * FDP-encoding gene orthologs are present but lacking gene organization; ** The FDP-encoding gene is splited into two genes, coding for a Class A FDP and flavin reductase, and situated sequentially in one polycistron; *** possess a Class A FDP; # possess two absolutely identical extra copies;
PCC 7120 become arrested, resulting in cell death, in the most severe and long-term fluctuating light conditions. Such phenomenon is mainly caused by Photosystem I (PSI) malfunction and concomitant oxidative stress induced by reactive oxygen species (ROS) generated during abrupt short-term increases in light intensity, as evidenced by high carbonylation levels of proteins
Summary
Flavodiiron proteins (FDPs), previously called A-type flavoproteins (Flv) [1], are a large family of enzymes sharing sequence similarity. The functional form of FDPs in anaerobic prokaryotes and eukaryotic protozoa has been resolved as a homodimer or homotetramer arranged in a “head to tail” configuration so that the diiron center of one monomer and the FMN in the other monomer closely contact each other, which ensures fast electron transfer between the cofactors. In addition to the common sequence core, some FDPs have C-terminal extensions. The majority of FDPs belong to Class A, which is the simplest type with the shortest extension sequences, representing the minimal core structure. These can be found in Bacteria, Archaea and Protozoa. The additional flavin reductase-like domain in this specific class makes it possible for nicotinamide adenine dinucleotide (phosphate), reduced form (NAD(P)H) to be directly used as an electron donor. In organisms containing respiratory oxidases (Escherichia coli, Desulfovibrio gigas, Desulfovibrio vulgaris, Moorella), FDPs are known to have either strict NO-reductase function or dual function, cooperating with respiratory oxidases in protection against O2 toxicity
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