Prenylcysteine -Carboxyl Methyltransferase in Suspension-Cultured Tobacco Cells¹

Dring N. Crowell^*, Stephanie E. Sen, and Stephen K. Randall

Department of Biology, Indiana University-Purdue University at Indianapolis, 723 West Michigan Street, Indianapolis, Indiana 46202 (D.N.C., S.K.R.); and Department of Chemistry, Indiana University-Purdue University at Indianapolis, 402 North Blackford Street, Indianapolis, Indiana 46202 (S.E.S.)

Isoprenylation is a posttranslational modification that is believed to be necessary, but not sufficient, for the efficient association of numerous eukaryotic cell proteins with membranes. Additional modifications have been shown to be required for proper intracellular targeting and function of certain isoprenylated proteins in mammalian and yeast cells. Although protein isoprenylation has been demonstrated in plants, postisoprenylation processing of plant proteins has not been described. Here we demonstrate that cultured tobacco (Nicotiana tabacum cv Bright Yellow-2) cells contain farnesylcysteine and geranylgeranylcysteine -carboxyl methyltransferase activities with apparent Michaelis constants of 73 and 21 µM for N-acetyl-S-trans,trans-farnesyl-L-cysteine and N-acetyl-S-all-trans-geranylgeranyl-L-cysteine, respectively. Furthermore, competition analysis indicates that the same enzyme is responsible for both activities. These results suggest that -carboxyl methylation is a step in the maturation of isoprenylated proteins in plants.

Plant Physiol. (1998) 118: 115-123
Copyright Clearance Center:   0032-0889/98/118//09
© 1998 American Society of Plant Physiologists

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