Early evolution of photosynthesis: clues from nitrogenase and chlorophyll iron proteins.

Abstract

Chlorophyll (Chl) is often viewed as having preceded bacteriochlorophyll (BChl) as the primary photoreceptor pigment in early photosynthetic systems because synthesis of Chl requires one fewer enzymatic reduction than does synthesis of BChl. We have conducted statistical DNA sequence analyses of the two reductases involved in Chl and BChl synthesis, protochlorophyllide reductase and chlorin reductase. Both are three-subunit enzymes in which each subunit from one reductase shares significant amino acid identity with a subunit of the other, indicating that the two enzymes are derived from a common three-subunit ancestral reductase. The "chlorophyll iron protein" subunits, encoded by the bchL and bchX genes in the purple bacterium Rhodobacter capsulatus, also share amino acid sequence identity with the nitrogenase iron protein, encoded by niff. When nitrogenase iron proteins are used as outgroups, the chlorophyll iron protein tree is rooted on the chlorin reductase lineage. This rooting suggests that the last common ancestor of all extant photosynthetic eubacteria contained BChl, not Chl, in its reaction center, and implies that Chl-containing reaction centers were a late invention unique to the cyanobacteria/chloroplast lineage.

[FeFe]-hydrogenase in Yellowstone National Park: evidence for dispersal limitation and phylogenetic niche conservatism

“…The corresponding putative chlL/ bchL sequences were imported into MEGA4 (version 4.0.1), translated in frame, and the inferred aminoacid sequences were aligned using the ClustalW application (Gonnet substitution matrix, default parameters) within the MEGA4 program. Putative ChlL/BchL sequences were screened for the presence of conserved signature catalytic residues as defined previously (Burke et al, 1993). Sequences that lacked these domains were discarded without further consideration, resulting in 94 sequences for use in identifying consensus regions.…”

The cyanobacterial genome core and the origin of photosynthesis

“…The extremely small number of photosynthetic proteins that are shared between different photosynthetic bacteria (Table 1) forced the phylogenetic analyses to rely on surrogate protein sets, such as the enzymes involved in (bacterio)chlorophyll biosynthesis (14). These analyses contributed to the understanding of the evolution of (bacterio)chlorophyll (17) but did not purport to reflect evolution of photosynthesis in general.…”

Substrate Recognition of Nitrogenase-like Dark Operative Protochlorophyllide Oxidoreductase from Prochlorococcus marinus

“…DPOR consists of three protein subunits that are termed ChlN, ChlB, and ChlL in chlorophyll-synthesizing organisms (10 -12) and BchN, BchB, and BchL in bacteriochlorophyll-synthesizing organisms (13). They share significant amino acid sequence similarities with the NifD, NifK, and NifH subunits of nitrogenase, respectively (12,14).…”