Structure, expression and phylogeny of phycobiliproteins in the chlorophyll a and b -containing prokaryote Prochlorococcus marinus
Hess, W.R.
Humboldt-Universität, Inst. für Biologie, Chausseestr. 117, D-10115 Berlin, Germany
The free-living marine organism Prochlorococcus marinus is characterised by the unique combination of chlorophyll a/b-protein complexes as the major photosynthetic light harvesting system, chlorophyll c, and the simultanous presence of a specific form of phycoerythrin. Recent results have uncovered the nature of the chlorophyll a/b-binding proteins in P. marinus as well as in Prochloron and in Prochlorothrix hollandica, the only two other known prokaryotes that use chlorophyll b.
The molecular analysis of P. marinus revealed the presence of a gene cluster containing eight genes for phycobiliproteins or polypeptides that are involved in synthesis and attachment of chromophoric groups. The gene organization in general resembles the situation in marine cyanobacteria of the Synechococcus type, although some features indicate specific constraints, e.g. to maintain a unusual small and compact genome. The data suggest a closer phylogenetic relatedness between the Prochlorococcus phycobiliproteins and those of marine cyanobacteria than between the former and any other phycoerythrin, consistent with current scenarios of Prochlorococcus evolution. However, the lack of phycobilisomes and the relatively high degeneration of the alpha- in contrast to the beta-chain of phycoerythrin in this organism are striking parallels to cryptomonadic algae.
Hess, W. R. et al. (1996) PNAS93: 11126-11130
LaRoche, J. et al.(1996) PNAS93: 15244-15248