Mechanistic diversity in the RuBisCO superfamily: a novel isomerization reaction catalyzed by the RuBisCO-like protein from Rhodospirillum rubrum

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.

Figure 1

Reactions catalyzed by members of the RuBisCO superfamily. A) RuBisCO carboxylation and oxygenation. B) DK-MTP tautomerase. C) RLP from R. rubrum.

Figure 2

¹H NMR spectra of the substrate and product. A) 5-Methylthio-D-ribulose 1-phosphate in D₂O. B) Reaction in D₂O and NMR in D₂O. C) Reactio4n in H₂O and NMR in D₂O. D) Reaction in H₂O and NMR in H₂O.

Figure 3

¹³C NMR spectrum of the product from reaction in H₂O and NMR in H₂O (1H NMR spectrum in Figure 2D).