A new class of type I protein geranylgeranyltransferase (GGTase I) inhibitor

Synthetic isoprenoid analogues for the study of prenylated proteins: Fluorescent imaging and proteomic applications

Protein prenylation is a posttranslational modification catalyzed by prenyltransferases involving the attachment of farnesyl or geranylgeranyl groups to residues near the C-termini of proteins. This irreversible covalent modification is important for membrane localization and proper signal transduction. Here, the use of isoprenoid analogues for studying prenylated proteins is reviewed. First, experiments with analogues containing small fluorophores that are alternative substrates for prenyltransferases are described. Those analogues have been useful for quantifying binding affinity and for the production of fluorescently labeled proteins. Next, the use of analogues that incorporate biotin, bioorthogonal groups or antigenic moieties is described. Such probes have been particularly useful for identifying proteins that are naturally prenylated within mammalian cells. Overall, the use of isoprenoid analogues has contributed significantly to the understanding of protein prenlation.

Rapid analysis of protein farnesyltransferase substrate specificity using peptide libraries and isoprenoid diphosphate analogues

Protein farnesytransferase (PFTase) catalyzes the farnesylation of proteins with a carboxy-terminal tetrapeptide sequence denoted as a Ca₁a₂X box. To explore the specificity of this enzyme, an important therapeutic target, solid-phase peptide synthesis in concert with a peptide inversion strategy was used to prepare two libraries, each containing 380 peptides. The libraries were screened using an alkyne-containing isoprenoid analogue followed by click chemistry with biotin azide and subsequent visualization with streptavidin-AP. Screening of the CVa₂X and CCa₂X libraries with Rattus norvegicus PFTase revealed reaction by many known recognition sequences as well as numerous unknown ones. Some of the latter occur in the genomes of bacteria and viruses and may be important for pathogenesis, suggesting new targets for therapeutic intervention. Screening of the CVa₂X library with alkyne-functionalized isoprenoid substrates showed that those prepared from C₁₀ or C₁₅ precursors gave similar results, whereas the analogue synthesized from a C₅ unit gave a different pattern of reactivity. Lastly, the substrate specificities of PFTases from three organisms (R. norvegicus, Saccharomyces cerevisiae, and Candida albicans) were compared using CVa₂X libraries. R. norvegicus PFTase was found to share more peptide substrates with S. cerevisiae PFTase than with C. albicans PFTase. In general, this method is a highly efficient strategy for rapidly probing the specificity of this important enzyme.

Structure of protein geranylgeranyltransferase-I from the human pathogen Candida albicans complexed with a lipid substrate

Protein geranylgeranyltransferase-I (GGTase-I) catalyzes the transfer of a 20-carbon isoprenoid lipid to the sulfur of a cysteine residue located near the C terminus of numerous cellular proteins, including members of the Rho superfamily of small GTPases and other essential signal transduction proteins. In humans, GGTase-I and the homologous protein farnesyltransferase (FTase) are targets of anticancer therapeutics because of the role small GTPases play in oncogenesis. Protein prenyltransferases are also essential for many fungal and protozoan pathogens that infect humans, and have therefore become important targets for treating infectious diseases. Candida albicans, a causative agent of systemic fungal infections in immunocompromised individuals, is one pathogen for which protein prenylation is essential for survival. Here we present the crystal structure of GGTase-I from C. albicans (CaGGTase-I) in complex with its cognate lipid substrate, geranylgeranylpyrophosphate. This structure provides a high-resolution picture of a non-mammalian protein prenyltransferase. There are significant variations between species in critical areas of the active site, including the isoprenoid-binding pocket, as well as the putative product exit groove. These differences indicate the regions where specific protein prenyltransferase inhibitors with antifungal activity can be designed.

Thematic review series: lipid posttranslational modifications. Structural biology of protein farnesyltransferase and geranylgeranyltransferase type I

More than 100 proteins necessary for eukaryotic cell growth, differentiation, and morphology require posttranslational modification by the covalent attachment of an isoprenoid lipid (prenylation). Prenylated proteins include members of the Ras, Rab, and Rho families, lamins, CENPE and CENPF, and the gamma subunit of many small heterotrimeric G proteins. This modification is catalyzed by the protein prenyltransferases: protein farnesyltransferase (FTase), protein geranylgeranyltransferase type I (GGTase-I), and GGTase-II (or RabGGTase). In this review, we examine the structural biology of FTase and GGTase-I (the CaaX prenyltransferases) to establish a framework for understanding the molecular basis of substrate specificity and mechanism. These enzymes have been identified in a number of species, including mammals, fungi, plants, and protists. Prenyltransferase structures include complexes that represent the major steps along the reaction path, as well as a number of complexes with clinically relevant inhibitors. Such complexes may assist in the design of inhibitors that could lead to treatments for cancer, viral infection, and a number of deadly parasitic diseases.

Massadine, a novel geranylgeranyltransferase type I inhibitor from the marine sponge Stylissa aff. massa

Massadine, a highly oxygenated alkaloid, was isolated from the marine sponge Stylissa aff. massa as an inhibitor of geranylgeranyltransferase type I (GGTase I). The structure of massadine has been deduced from spectral data. Massidine inhibited GGTase I from Candida albicans with an IC(50) value of 3.9 microM. [structure: see text]