ABSTRACT
Processing of Plant Proteins .............................................................. 254 10.3 Identification and Functional Characterization of Prenylated
Plant Proteins ..................................................................................... 259 10.4 ROPs .................................................................................................. 262 10.5 RABs .................................................................................................. 263 10.6 ANJ1 .................................................................................................. 263 10.7 V-SNARES ........................................................................................ 263 10.8 AIG1 .................................................................................................. 264 10.9 APETALA1 ....................................................................................... 265 10.10 NAP1 ................................................................................................. 267 10.11 MUBs ................................................................................................. 267 10.12 AUX2-11 ........................................................................................... 268 10.13 Other Biological Roles for Protein Prenylation in Plants .................. 269 Keywords ....................................................................................................... 270 References ...................................................................................................... 271
Protein prenylation is the posttranslational, covalent attachment of an isoprenoid lipid to a protein. Usually, prenylated proteins are modified by thioether linkage of a carboxyl-terminal cysteine residue to a fifteen carbon farnesyl or a twenty carbon geranylgeranyl group (Clarke, 1992; Zhang and Casey, 1996; Randall and Crowell, 1999; Rodríguez-Concepción et al., 1999; Crowell, 2000; Galichet and Gruissem, 2003). Three distinct protein prenyltransferases, with different substrate preferences, have been described in plants (e.g., Arabidopsis, tomato, tobacco, pea), animals, and yeast. Protein farnesyltransferase (PFT) is a heterodimeric enzyme consisting of a-and b-subunits. This enzyme catalyzes the transfer of a farnesyl moiety from farnesyl diphosphate (FPP) to the cysteine residue of a carboxyl-terminal CaaX motif, where “C” is cysteine, “a” is an aliphatic amino acid, and “X” is usually methionine, glutamine, alanine, cysteine or serine (Reid et al., 2004). PFT is a zinc metalloenzyme and requires magnesium for activity (Clarke, 1992; Zhang and Casey, 1996; Crowell, 2000). Protein geranylgeranyltransferase type I (PGGTI) is also a heterodimeric enzyme consisting of an a - subunit identical to that of PFT and a distinct b-subunit. This enzyme catalyzes the transfer of a geranylgeranyl moiety from geranylgeranyl diphosphate (GGPP) to the cysteine residue of a carboxyl-terminal CaaX motif, where “ X” is leucine or isoleucine (Reid et al., 2004). Like PFT, PGGTI is a zinc metalloenzyme, but does not require magnesium for activity (Clarke, 1992; Zhang and Casey, 1996; Crowell, 2000). Protein geranylgeranyltransferase type II (PGGTII), or Rab geranylgeranyltransferase, consists of distinct a - and bsubunits and catalyzes the transfer of a geranylgeranyl moiety from GGPP to one or two cysteine residues at the carboxyl terminus of a Rab GTPase that is associated with the Rab Escort Protein (REP). Rab GTPases typically have a CCXX, XCXC, XCCX, or XXCC motif at the carboxyl terminus, although some possess a carboxyl-terminal CaaX motif (Clarke, 1992; Zhang and Casey, 1996; Crowell, 2000; Leung et al., 2006; Leung et al., 2007).
