the caax specificities of arabidopsis protein prenyltransferases explain era1 and ggb phenotypes的caax拟南芥蛋白质的特异性prenyltransferases解释era1和ggb表型.pdf

Andrews et al. BMC Plant Biology 2010, 10:118 /1471-2229/10/118 R E S E A R C H A R T I C L E Open Access Research article The CaaX specificities of Arabidopsis protein prenyltransferases explain era1 and ggb phenotypes 1 2,3 1 Michelle Andrews , David H Huizinga and Dring N Crowell* Abstract Background: Protein prenylation is a common post-translational modification in metazoans, protozoans, fungi, and plants. This modification, which mediates protein-membrane and protein-protein interactions, is characterized by the covalent attachment of a fifteen-carbon farnesyl or twenty-carbon geranylgeranyl group to the cysteine residue of a carboxyl terminal CaaX motif. In Arabidopsis, era1 mutants lacking protein farnesyltransferase exhibit enlarged meristems, supernumerary floral organs, an enhanced response to abscisic acid (ABA), and drought tolerance. In contrast, ggb mutants lacking protein geranylgeranyltransferase type 1 exhibit subtle changes in ABA and auxin responsiveness, but develop normally. Results: We have expressed recombinant Arabidopsis protein farnesyltransferase (PFT) and protein geranylgeranyltransferase type 1 (PGGT1) in E. coli and characterized purified enzymes with respect to kinetic constants and substrate specificities. Our results indicate that, whereas PFT exhibits little specificity for the terminal amino acid of the CaaX motif, PGGT1 exclusively prenylates CaaX proteins with a leucine in the terminal position. Moreover, we found that different substrates exhibit similar Km but different kcat values in the presence of PFT and PGGT1, indicating that substrate specificities are determined primarily by reactivity rather than binding affinity. Conclusions: The data presented here potentially explain the relatively st