Topology of mammalian isoprenylcysteine carboxyl methyltransferase determined in live cells with a fluorescent probe.

Journal Article (Journal Article)

Isoprenylcysteine carboxyl methyltransferase (Icmt) is a highly conserved enzyme that methyl esterifies the alpha carboxyl group of prenylated proteins including Ras and related GTPases. Methyl esterification neutralizes the negative charge of the prenylcysteine and thereby increases membrane affinity. Icmt is an integral membrane protein restricted to the endoplasmic reticulum (ER). The Saccharomyces cerevisiae ortholog, Ste14p, traverses the ER membrane six times. We used a novel fluorescent reporter to map the topology of human Icmt in living cells. Our results indicate that Icmt traverses the ER membrane eight times, with both N and C termini disposed toward the cytosol and with a helix-turn-helix structure comprising transmembrane (TM) segments 7 and 8. Several conserved amino acids that map to cytoplasmic portions of the enzyme are critical for full enzymatic activity. Mammalian Icmt has an N-terminal extension consisting of two TM segments not found in Ste14p and therefore likely to be regulatory. Icmt is a target for anticancer drug discovery, and these data may facilitate efforts to develop small-molecule inhibitors.

Full Text

Duke Authors

Cited Authors

  • Wright, LP; Court, H; Mor, A; Ahearn, IM; Casey, PJ; Philips, MR

Published Date

  • April 2009

Published In

Volume / Issue

  • 29 / 7

Start / End Page

  • 1826 - 1833

PubMed ID

  • 19158273

Pubmed Central ID

  • PMC2655619

Electronic International Standard Serial Number (EISSN)

  • 1098-5549

Digital Object Identifier (DOI)

  • 10.1128/MCB.01719-08


  • eng

Conference Location

  • United States