Predicting the substrates of cloned plant O-methyltransferases.

Plant O-methyltransferases (OMTs) have important roles in secondary metabolite biosynthesis. Sequencing projects and homology-based cloning strategies yield sequences for proteins with similarities to known OMTs, but the identification of the physiological substrates is not trivial. We investigated with a cDNA cloned from Catharanthus roseus the possibilities for predicting the substrates of OMTs, using the information from previous work and two newly identified motifs that were based on information from the crystal structures of two plant OMTs. The results, confirmed by functional analysis of the recombinant protein, indicated that a careful analysis of the deduced protein sequence can provide clues for predicting the substrates of cloned OMTs.