Mechanistic Diversity in the RuBisCO Superfamily: A Novel Isomerization Reaction Catalyzed by the RuBisCO-like Protein from Rhodospirillum rubrum

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Abstract
Some homologues of d-ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) do not catalyze carboxylation and are designated RuBisCO-like proteins (RLPs). The RLP from Rhodospirillum rubrum (gi:83593333) catalyzes a novel isomerization reaction (overall 1,3-proton transfer reaction; likely, two 1,2-proton transfer reactions) that converts 5-methylthio-d-ribulose 1-phosphate to a 3:1 mixture of 1-methylthioxylulose 5-phosphate and 1-methylthioribulose 5-phosphate. Disruption of the gene encoding the RLP abolishes the ability of R. rubrum to utilize 5′-methylthioadenosine as a sole sulfur source, implicating a new, as-yet-uncharacterized, pathway for sulfur salvage.