Identification and isoprenylation of plant GTP-binding proteins

✍ Scribed by Brenda Biermann; Stephen K. Randall; Dring N. Crowell

• Publisher: Springer
• Year: 1996
• Tongue: English
• Weight: 822 KB
• Volume: 31
• Category: Article
• ISSN: 0167-4412
• DOI: 10.1007/bf00040720

✦ Synopsis

To identify isoprenylated plant GTP-binding proteins, Arabidopsis thaliana and Nicotiana tabacum cDNA expression libraries were screened for cDNA-encoded proteins capable of binding [32p]GTP in vitro. ATGB2, an Arabidopsis homologue of the GTP-binding protein Rab2, was found to bind GTP in vitro and to be a substrate for a geranylgeranyl:protein transferase (GGTase) present in plant extracts. The carboxyl terminus of this protein contains a -GCCG sequence, which has not previously been shown to be recognized by any prenyl:protein transferase (PTase), but which most closely resembles that isoprenylated by the type II GGTase (-XXCC, -XCXC, or -CCXX).

In vitro geranylgeranylation of an Arabidopsis Rabl protein containing a carboxyl-terminal -CCGQ sequence confirmed the presence of a type II GGTase-like activity in plant extracts. Several other proteins were also identified by in vitro GTP binding, including Arabidopsis and tobacco homologues of Rab I 1, ARF (ADP-ribosylation factor) and Sat proteins, as well as a novel 22 kDa Arabidopsis protein (ATG81 ). This 22 kDa protein had consensus GTPbinding motifs and bound GTP with high specificity, but its structure was not closely related to that of any known GTP-binding protein (it most resembled proteins within the ARF/Sar and G protein (~-subunit superfamilies).