Abstract
Phylogenetic analysis of translated rbcL sequences divides ribulose-1,5-bisphasphate carboxylase/oxygenase (RuBisCO) into four clades. Forms I through III include the amino acid residues that are required for catalytic activity of RuBisCO and are capable of catalyzing both the carboxylation and oxygenation of ribulose-1,5-bisphasphate. Form IV lacks the residues involved in binding of the phosphate group on C5 and the functional loop 6 conserved in photosynthetic RuBisCO, and has no carboxylation and oxygenation activity. Form IV is thereby referred to as the RuBisCO-like protein (RLP). We found that RLP from Bacillus subtilis catalyzed the 2,3-diketo-5-methylthiopentyl-1-phosphate enolase reaction in the methionine salvage pathway. We created several mutated RLPs where a few lysine residues essential for RuBisCO and some residues were changed to other amino acid residues. Some mutated RLPs lost the enolase activity. Thus well conserved, catalytic lysines of RuBisCO also play key roles in RLP.
