Geranylgeranyltransferase I of Candida albicans: null mutants or enzyme inhibitors produce unexpected phenotypes

Geranylgeranyltransferase I (GGTase I) catalyzes the transfer of a prenyl group from geranylgeranyl diphosphate to the carboxy-terminal cysteine of proteins with a motif referred to as a CaaX box (C, cysteine; a, usually aliphatic amino acid; X, usually L). The alpha and beta subunits of GGTase I from Saccharomyces cerevisiae are encoded by RAM2 and CDC43, respectively, and each is essential for viability. We are evaluating GGTase I as a potential target for antimycotic therapy of the related yeast, Candida albicans, which is the major human pathogen for disseminated fungal infections. Recently we cloned CaCDC43, the C. albicans homolog of S. cerevisiae CDC43. To study its role in C. albicans, both alleles were sequentially disrupted in strain CAI4. Null Cacdc43 mutants were viable despite the lack of detectable GGTase I activity but were morphologically abnormal. The subcellular distribution of two GGTase I substrates, Rho1p and Cdc42p, was shifted from the membranous fraction to the cytosolic fraction in the cdc43 mutants, and levels of these two proteins were elevated compared to those in the parent strain. Two compounds that are potent GGTase I inhibitors in vitro but that have poor antifungal activity, J-109,390 and L-269,289, caused similar changes in the distribution and quantity of the substrate. The lethality of an S. cerevisiae cdc43 mutant can be suppressed by simultaneous overexpression of RHO1 and CDC42 on high-copy-number plasmids (Y. Ohya et al., Mol. Biol. Cell 4:1017, 1991; C. A. Trueblood, Y. Ohya, and J. Rine, Mol. Cell. Biol. 13:4260, 1993). Prenylation presumably occurs by farnesyltransferase (FTase). We hypothesize that Cdc42p and Rho1p of C. albicans can be prenylated by FTase when GGTase I is absent or limiting and that elevation of these two substrates enables them to compete with FTase substrates for prenylation and thus allows sustained growth.     

Expression and characterization of protein geranylgeranyltransferase type I from the pathogenic yeast Candida albicans and identification of yeast selective enzyme inhibitors

Protein geranylgeranyltransferase type I (GGTase I) is a heterodimeric zinc metalloenzyme catalyzing protein geranylgeranylation at cysteine residues present in C-terminal signature sequences referred to as CaaX (X=Leu) motifs. We have studied GGTase I as a potential antifungal target and recently reported its purification and cloning from the yeast Candida albicans (Ca GGTase I), an important human pathogen. Here, we report the high yield bacterial expression of Ca GGTase I by coexpression of maltose binding protein fusion proteins of both the alpha (Ram2p) and beta (Cdc43p) subunits. The cleaved and purified recombinant Ca GGTase I was demonstrated to be functional and structurally intact as judged by the presence of one equivalent of a tightly bound zinc atom and the near stoichiometric formation, isolation and catalytic turnover of a geranylgeranyl pyrophosphate-GGTase I complex. Kinetic analysis was performed with a native substrate protein, Candida Cdc42p, which exhibited significant pH dependent substrate inhibition, a feature not observed with other Ca GGTase I substrates. Prenyl acceptor substrate specificity was studied with a series of peptides in which both the CaaX motif, and the sequence preceding it, were varied. The prenyl acceptor K(M)s were found to vary nearly 100-fold, with biotinyl-TRERKKKKKCVIL, modeled after a presumably geranylgeranylated Candida protein, Crl1p (Rho4p), being the optimal substrate. A screen for inhibitors of Ca GGTase I identified compounds showing selectivity for the Candida versus human GGTase I. The most potent and selective compound, L-689230, had an IC(50) of 20 nM and >12,500-fold selectivity for Ca GGTase I. The lack of significant anti-Candida activity for any of these inhibitors is consistent with the recent finding that GGTase I is not required for C. albicans viability [R. Kelly et al., J. Bacteriol. 182 (2000) 704-713].     

Synthesis and evaluation of GGPP geometric isomers: divergent substrate specificities of FTase and GGTase I.

A stereocontrolled synthetic route has been used to prepare two of the geometric isomers of all-trans-GGPP. Neither of these isomers is effective substrates for mammalian GGTase I, but 3 is a potent inhibitor of this enzyme (IC(50)=100 nM). Surprisingly, both compounds are effective substrates for mammalian FTase.     

Prenyloxyphenylpropanoids as novel lead compounds for the selective inhibition of geranylgeranyl transferase I

In this study, we synthesized some natural and semisynthetic prenyloxyphenylpropanoids (e.g., coumarins and cinnamic acid derivatives) and we assessed their in vitro inhibitory activity against farnesyl transferase (FTase) and geranylgeranyl transferase I (GGTase I). No compound was an effective inhibitor of FTase, while farnesyloxycinnamic acids were shown to selectively inhibit GGTase I with IC(50) values ranging from 28 to 39 microM.     

Identification of a novel phosphonocarboxylate inhibitor of Rab geranylgeranyl transferase that specifically prevents Rab prenylation in osteoclasts and macrophages

Nitrogen-containing bisphosphonate drugs inhibit bone resorption by inhibiting FPP synthase and thereby preventing the synthesis of isoprenoid lipids required for protein prenylation in bone-resorbing osteoclasts. NE10790 is a phosphonocarboxylate analogue of the potent bisphosphonate risedronate and is a weak anti-resorptive agent. Although NE10790 was a poor inhibitor of FPP synthase, it did inhibit prenylation in J774 macrophages and osteoclasts, but only of proteins of molecular mass approximately 22-26 kDa, the prenylation of which was not affected by peptidomimetic inhibitors of either farnesyl transferase (FTI-277) or geranylgeranyl transferase I (GGTI-298). These 22-26-kDa proteins were shown to be geranylgeranylated by labelling J774 cells with [(3)H]geranylgeraniol. Furthermore, NE10790 inhibited incorporation of [(14)C]mevalonic acid into Rab6, but not into H-Ras or Rap1, proteins that are modified by FTase and GGTase I, respectively. These data demonstrate that NE10790 selectively prevents Rab prenylation in intact cells. In accord, NE10790 inhibited the activity of recombinant Rab GGTase in vitro, but did not affect the activity of recombinant FTase or GGTase I. NE10790 therefore appears to be the first specific inhibitor of Rab GGTase to be identified. In contrast to risedronate, NE10790 inhibited bone resorption in vitro without markedly affecting osteoclast number or the F-actin "ring" structure in polarized osteoclasts. However, NE10790 did alter osteoclast morphology, causing the formation of large intracellular vacuoles and protrusion of the basolateral membrane into large, "domed" structures that lacked microvilli. The anti-resorptive activity of NE10790 is thus likely due to disruption of Rab-dependent intracellular membrane trafficking in osteoclasts.     

Lysine beta311 of protein geranylgeranyltransferase type I partially replaces magnesium

Protein geranylgeranyltransferase type I (GGTase I) catalyzes the attachment of a geranylgeranyl lipid group near the carboxyl terminus of protein substrates. Unlike protein farnesyltransferase (FTase) and protein geranylgeranyltransferase type II, which require both Zn(II) and Mg(II) for maximal turnover, GGTase I turnover is dependent only on Zn(II). In FTase, the magnesium ion is coordinated by aspartate beta352 and the diphosphate of farnesyl diphosphate to stabilize the developing charge in the transition state (Pickett, J. S., Bowers, K. E., and Fierke, C. A. (2003) J. Biol. Chem. 278, 51243-51250). In GGTase I, lysine beta311 is substituted for this aspartate and is proposed to replace the catalytic function of Mg(II) (Taylor, J. S., Reid, T. S., Terry, K. L., Casey, P. J., and Beese, L. S. (2003) EMBO J. 22, 5963-5974). Here we demonstrate that the prenylation rate constant catalyzed by wild type GGTase I (k(chem) = 0.18 +/- 0.02 s(-1)) is not dependent on Mg(II), is approximately 20-fold slower than the maximal rate constant catalyzed by FTase, and has a single pKa of 6.4 +/- 0.1, likely reflecting deprotonation of the peptide thiol. Mutation of lysine beta311 in GGTase I to alanine (Kbeta311A) or aspartate (Kbeta311D) decreases the k(chem) in the absence of magnesium 9-41-fold without significantly affecting the binding affinity of either substrate. Furthermore, the geranylgeranylation rate constant is enhanced by the addition of Mg(II) for Kbeta311A and Kbeta311D GGTase I 2-5-fold compared with wild type GGTase I with K(Mg) of 140 +/- 10 mm and 6.4 +/- 0.8 mm, respectively. These results demonstrate that lysine beta311 of GGTase I partially replaces the catalytic function of Mg(II) observed in FTase.     

Potentiation of Rho-A-mediated lysophosphatidic acid activity by hyperinsulinemia

We have shown previously that insulin promotes phosphorylation and activation of farnesyltransferase and geranylgeranyltransferase (GGTase) II. We have now examined the effect of insulin on geranylgeranyltransferase I in MCF-7 breast cancer cells. Insulin increased GGTase I activity 3-fold and augmented the amounts of geranylgeranylated Rho-A by 18%. Both effects of the insulin were blocked by an inhibitor of GGTase I, GGTI-286. The insulin-induced increases in the amounts of geranylgeranylated Rho-A resulted in potentiation of the Rho-A-mediated effects of lysophosphatidic acid (LPA) on a serum response element-luciferase construct. Preincubation of cells with insulin augmented the LPA-stimulated serum response element-luciferase activation to 12-fold, compared with just 6-fold for LPA alone (p < 0.05). The potentiating effect of insulin was dose-dependent, inhibited by GGTI-286 and not mimicked by insulin-like growth factor-1. We conclude that insulin activates GGTase I, increases the amounts of geranylgeranylated Rho-A protein, and potentiates the Rho-A-dependent nuclear effects of LPA in MCF-7 breast cancer cells.     

Suppression of yeast geranylgeranyl transferase I defect by alternative prenylation of two target GTPases, Rho1p and Cdc42p.

Geranylgeranyl transferase I (GGTase I), which modifies proteins containing the sequence Cys-Ali-Ali-Leu (Ali: aliphatic) at their C-termini, is indispensable for growth in the budding yeast Saccharomyces cerevisiae. We report here that GGTase I is no longer essential when Rho1p and Cdc42p are simultaneously overproduced. The lethality of a GGTase I deletion is most efficiently suppressed by provision of both Rho1p and Cdc42p with altered C-terminal sequences (Cys-Ali-Ali-Met) corresponding to the C-termini of substrates of farnesyl transferase (FTase). Under these circumstances, the FTase, normally not essential for growth of yeast, becomes essential.     

Impaired geranylgeranyltransferase‐I regulation reduces membrane‐associated Rho protein levels in aged mouse brain

Synaptic impairment rather than neuronal loss may be the leading cause of cognitive dysfunction in brain aging. Certain small Rho‐GTPases are involved in synaptic plasticity, and their dysfunction is associated with brain aging and neurodegeneration. Rho‐GTPases undergo prenylation by attachment of geranylgeranylpyrophosphate (GGPP) catalyzed by GGTase‐I. We examined age‐related changes in the abundance of Rho and Rab proteins in membrane and cytosolic fractions as well as of GGTase‐I in brain tissue of 3‐ and 23‐month‐old C57BL/6 mice. We report a shift in the cellular localization of Rho‐GTPases toward reduced levels of membrane‐associated and enhanced cytosolic levels of those proteins in aged mouse brain as compared with younger mice. The age‐related reduction in membrane‐associated Rho proteins was associated with a reduction in GGTase‐Iβ levels that regulates binding of GGPP to Rho‐GTPases. Proteins prenylated by GGTase‐II were not reduced in aged brain indicating a specific targeting of GGTase‐I in the aged brain. Inhibition of GGTase‐I in vitro modeled the effects of aging we observed in vivo. We demonstrate for the first time a decrease in membrane‐associated Rho proteins in aged brain in association with down‐regulation of GGTase‐Iβ. This down‐regulation could be one of the mechanisms causing age‐related weakening of synaptic plasticity.

     

Upstream polybasic region in peptides enhances dual specificity for prenylation by both farnesyltransferase and geranylgeranyltransferase type I

Protein farnesyltransferase (FTase) and protein geranylgeranyltransferase type I (GGTase I) catalyze the attachment of a farnesyl or geranylgeranyl lipid, respectively, near the C-terminus of their protein substrates. FTase and GGTase I differ in both their substrate specificity and magnesium dependence, where the activity of FTase, but not GGTase I, is activated by magnesium. Many protein substrates of these enzymes contain an upstream polybasic region that is proposed to increase the affinity of the substrate and aid in plasma membrane association. Here, we demonstrate that the addition of an upstream polybasic region to a peptide substrate enhances the binding affinity of FTase approximately 4-fold for the peptide but diminishes the catalytic efficiency of the reaction, reflected by decreases in both the prenylation rate constant and kcat/KM. Specifically, the prenylation rate constant decreases 7-fold at 5 mM MgCl2 for the peptide KKKSKTKCVIM (C-terminal sequence of K-Ras4B) in comparison to TKCVIM. This decrease is accompanied by an alteration in the dependence on magnesium, as the K(Mg) increases from 2.2 +/- 0.1 mM for TKCVIM to 11.5 +/- 0.1 mM for KKKSKTKCVIM. The presence of an upstream polybasic region does not significantly affect GGTase I-catalyzed reactions, as only minimal changes are seen in Kd, kcat/KM, and k(chem) values. Thus, the presence of an upstream polybasic region enhances the dual prenylation of these substrates, by decreasing the catalytic efficiency of farnesylation catalyzed by FTase to a level comparable to that of geranylgeranylation catalyzed by GGTase I.     

Dominant negative alpha-subunit of FTase inhibits effects of insulin and IGF-I in MCF-7 cells

We recently designed a dominant negative (DN) farnesyltransferase (FTase)/geranyl-gerahyltransferase I (GGTase I) alpha-subunit that when expressed in vascular smooth muscle cells decreased insulin-stimulated phosphorylation of FTase, FTase activity, amounts of farnesylated p21Ras, DNA synthesis, and cell migration. Currently, we explored the inhibitory effects of DN FTase/GGTase I alpha-subunit in MCF-7 cells on IGF-1- and insulin-stimulated DNA synthesis and cell proliferation. Expression of the DN FTase/GGTase I alpha-subunit completely blocked IGF-1- and insulin-stimulated BrdU incorporation and cell count. DN FTase/GGTase I alpha-subunit inhibited insulin-stimulated phosphorylation of FTase/GGTase I alpha-subunit, FTase and GGTase I activity, and prenylation of p21Ras and RhoA. Expression of DN FTase/GGTase I alpha-subunit diminished IGF-1- and insulin-stimulated phosphorylation of ERK (extracellular signal-regulated kinase), but had no effect on IGF-1- and insulin-stimulated phosphorylation of Akt. Taken together, these data suggest that DN FTase/GGTase I alpha-subunit can assuage the mitogenic effects of IGF-1 and insulin on MCF-7 breast cancer cells.     

Synthesis and evaluation of hydroxyproline-derived isoprenyltransferase inhibitors.

A series of peptidomimetics based on a hydroxyproline scaffold was prepared and evaluated for inhibition of farnesyltransferase and geranylgeranyltransferase I in both enzymatic and cell-based assays. A number of analogs were potent and selective inhibitors of FTase, while one compound (22) was nonselective in the enzymatic assays but eight-fold selective for inhibition of GGTase in the cellular assay (IC50 = 0.39 microM).     

Novel and selective imidazole-containing biphenyl inhibitors of protein farnesyltransferase

A series of imidazole-containing biphenyls was prepared and evaluated in vitro for inhibition of FTase and cellular Ras processing. Several of these analogues, such as 21, are potent inhibitors of FTase (<1nM), FTase/GGTase selective (>300-fold) and cellularly active (相似文献   

Peptide specificity of protein prenyltransferases is determined mainly by reactivity rather than binding affinity

Protein farnesyltransferase (FTase) and protein geranylgeranyltransferase type I (GGTase I) catalyze the attachment of lipid groups from farnesyl diphosphate and geranylgeranyl diphosphate, respectively, to a cysteine near the C-terminus of protein substrates. FTase and GGTase I modify several important signaling and regulatory proteins with C-terminal CaaX sequences ("C" refers to the cysteine residue that becomes prenylated, "a" refers to any aliphatic amino acid, and "X" refers to any amino acid). In the CaaX paradigm, the C-terminal X-residue of the protein/peptide confers specificity for FTase or GGTase I. However, some proteins, such as K-Ras, RhoB, and TC21, are substrates for both FTase and GGTase I. Here we demonstrate that the C-terminal amino acid affects the binding affinity of K-Ras4B-derived hexapeptides (TKCVIX) to FTase and GGTase I modestly. In contrast, reactivity, as indicated by transient and steady-state kinetics, varies significantly and correlates with hydrophobicity, volume, and structure of the C-terminal amino acid. The reactivity of FTase decreases as the hydrophobicity of the C-terminal amino acid increases whereas the reactivity of GGTase I increases with the hydrophobicity of the X-group. Therefore, the hydrophobicity, as well as the structure of the X-group, determines whether peptides are specific for farnesylation, geranylgeranylation, or dual prenylation.     

Synthesis and evaluation of 3- and 7-substituted geranylgeranyl pyrophosphate analogs

Protein prenyl transferases have been a focus of anti-cancer drug discovery in recent years due to their roles in post-translational modification of small GTP binding proteins. Attention is now turning to the development of GGTase I inhibitors. Here, we present the synthesis and biological evaluation of four GGPP analogs versus mammalian GGTase I and the discovery that 7-allyl GGPP is a surprisingly efficient GGTase I substrate.     

Insulin signals to prenyltransferases via the Shc branch of intracellular signaling

We assessed the roles of insulin receptor substrate-1 (IRS-1) and Shc in insulin action on farnesyltransferase (FTase) and geranylgeranyltransferase I (GGTase I) using Chinese hamster ovary (CHO) cells that overexpress wild-type human insulin receptors (CHO-hIR-WT) or mutant insulin receptors lacking the NPEY domain (CHO-DeltaNPEY) or 3T3-L1 fibroblasts transfected with adenoviruses that express the PTB or SAIN domain of IRS-1 and Shc, the pleckstrin homology (PH) domain of IRS-1, or the Src homology 2 (SH2) domain of Shc. Insulin promoted phosphorylation of the alpha-subunit of FTase and GGTase I in CHO-hIR-WT cells, but was without effect in CHO-DeltaNPEY cells. Insulin increased FTase and GGTase I activities and the amounts of prenylated Ras and RhoA proteins in CHO-hIR-WT (but not CHO-DeltaNPEY) cells. Overexpression of the PTB or SAIN domain of IRS-1 (which blocked both IRS-1 and Shc signaling) prevented insulin-stimulated phosphorylation of the FTase and GGTase I alpha-subunit activation of FTase and GGTase I and subsequent increases in prenylated Ras and RhoA proteins. In contrast, overexpression of the IRS-1 PH domain, which impairs IRS-1 (but not Shc) signaling, did not alter insulin action on the prenyltransferases, but completely inhibited the insulin effect on the phosphorylation of IRS-1 and on the activation of phosphatidylinositol 3-kinase and Akt. Finally, overexpression of the Shc SH2 domain completely blocked the insulin effect on FTase and GGTase I activities without interfering with insulin signaling to MAPK. These data suggest that insulin signaling from its receptor to the prenyltransferases FTase and GGTase I is mediated by the Shc pathway, but not the IRS-1/phosphatidylinositol 3-kinase pathway. Shc-mediated insulin signaling to MAPK may be necessary (but not sufficient) for activation of prenyltransferase activity. An additional pathway involving the Shc SH2 domain may be necessary to mediate the insulin effect on FTase and GGTase I.     

Inhibition of Achromobacter protease I by lysinal derivatives.

Z-Val-, Z-Pro-, Z-Leu-Leu-, and Z-Leu-Pro-lysinals and BZ-DL-lysinal were chemically synthesized and tested as novel inhibitors for Achromobacter protease I (API), a lysine-specific serine protease. Among the lysinal derivatives tested, Z-Val-lysinal was the most potent competitive inhibitor, its Ki being estimated as 6.5 nM in an esterolytic assay with Tos-Lys-OMe. In an amidolytic assay, Z-Leu-Leu-lysinal was the most potent inhibitor and the apparent mode of inhibition was non-competitive. The Kis of the other lysinal derivatives in both esterolytic and amidolytic assays were more than 10(3) times lower than that of leupeptin. Z-Val-lysinol, lacking the aldehyde group, was a poor competitive inhibitor. These results suggest that acyl-, acylaminoacyl-, and acylpeptidyllysinals function as a transition-state inhibitor for Achromobacter protease I.     

Characterization of the geranylgeranyl transferase type I from Schizosaccharomyces pombe

The Schizosaccharomyces pombe cwg2⁺ gene encodes the β-subunit of geranylgeranyl transferase I (GGTase I), which participates in the post-translational C-terminal modification of several small GTPases, allowing their targeting to the membrane. Using the two-hybrid system, we have identified the cwp1⁺ gene that encodes the α-subunit of the GGTase I. cwp1p interaction with cwg2p was mapped to amino acids 1–244 or 137–294 but was not restricted to amino acids 137–244. The genomic cwp1⁺ was isolated and sequenced. It has two putative open reading frames of 677 and 218 bp, separated by a 51 bp intron. The predicted amino acid sequence shows significant similarity to GGTase I α-subunits from different species. However, complementation of Saccharomyces cerevisiae ram2-1 mutant by overexpressing the cwp1⁺ gene was not possible. Expression of both cwg2⁺ and cwp1⁺ in Escherichia coli allowed ‘in vitro’ reconstitution of the GGTase I activity. S. pombe cells expressing the mutant enzyme containing the cwg2-1 mutation do not grow at 37°C, but the growth defect can be suppressed by the addition of sorbitol. Actin immunostaining of the cwg2-1 mutant strain grown at 37°C showed an abnormal distribution of actin patches. The cwg2-1 mutation was identified as a guanine to adenine substitution at nucleotide 604 of the coding region, originating the change A202T in the cwg2p. Deletion of the cwg2 gene is lethal; Δcwg2 spores can divide two or three times before losing viability. Most cells have aberrant morphology and septation defects. Overexpression of the rho1G15VC199R double-mutant allele in S. pombe caused loss of polarity but was not lethal and did not render the (1–3)β-D -glucan synthase activity independent of GTP. Therefore, geranylgeranylation of rho1p is required for the appropriate function of this GTPase.     

Inhibition of GGTase‐I and FTase disrupts cytoskeletal organization of human PC‐3 prostate cancer cells

The mevalonate synthesis pathway produces intermediates for isoprenylation of small GTPases, which are involved in the regulation of actin cytoskeleton and cell motility. Here, we investigated the role of the prenylation transferases in the regulation of the cytoskeletal organization and motility of PC‐3 prostate cancer cells. This was done by using FTI‐277, GGTI‐298 or NE‐10790, the specific inhibitors of FTase (farnesyltransferase), GGTase (geranylgeranyltransferase)‐I and ‐II, respectively. Treatment of PC‐3 cells with GGTI‐298 and FTI‐277 inhibited migration and invasion in a time‐ and dose‐dependent manner. This was associated with disruption of F‐actin organization and decreased recovery of GFP–actin. Immunoblot analysis of various cytoskeleton‐associated proteins showed that the most striking change in GGTI‐298‐ and FTI‐277‐treated cells was a markedly decreased level of total and phosphorylated cofilin, whereas the level of cofilin mRNA was not decreased. The treatment of PC‐3 cells with GGTI‐298 also affected the dynamics of GFP–paxillin and decreased the levels of total and phosphorylated paxillin. The levels of phosphorylated FAK (focal adhesion kinase) and PAK (p‐21‐associated kinase)‐2 were also lowered by GGTI‐298, but levels of paxillin or FAK mRNAs were not affected. In addition, GGTI‐298 had a minor effect on the activity of MMP‐9. RNAi knockdown of GGTase‐Iβ inhibited invasion, disrupted F‐actin organization and decreased the level of cofilin in PC‐3 cells. NE‐10790 did not have any effect on PC‐3 prostate cancer cell motility or on the organization of the cytoskeleton. In conclusion, our results demonstrate the involvement of GGTase‐I‐ and FTase‐catalysed prenylation reactions in the regulation of cytoskeletal integrity and motility of prostate cancer cells and suggest them as interesting drug targets for development of inhibitors of prostate cancer metastasis.     

A Homology Based Model and Virtual Screening of Inhibitors for Human Geranylgeranyl Transferase 1 (GGTase1)

Protein prenylation is a post translational modification that is indispensable for Ras–Rho mediated tumorigenesis. In mammals, three enzymes namely protein farnesyltransferase (FTase), geranylgeranyl transferase1 (GGTase1), and geranylgeranyl transferase2 (GGTase2) were found to be involved in this process. Usually proteins of Ras family will be farnesylated by FTase, Rho family will be geranylgeranylated by GGTase1. GGTase2 is exclusive for geranylgeranylating Rab protein family. FTase inhibitors such as FTI- 277 are potent anti-cancer agents in vitro. In vivo, mutated Ras proteins can either improve their affinity for FTase active site or undergo geranylgeranylation which confers resistance and no activity of FTase inhibitors. This led to the development of GGTase1 inhibitors. A well-defined 3-D structure of human GGTase1 protein is lacking which impairs its in silico and rational designing of inhibitors. A 3-D structure of human GGTase1 was constructed based on primary sequence available and homology modeling to which pubchem molecules library was virtually screened through AutoDock Vina. Our studies show that natural compounds Camptothecin (-8.2 Kcal/mol), Curcumin (-7.3 Kcal/mol) have higher binding affinities to GGTase-1 than that of established peptidomimetic GGTase-1 inhibitors such as GGTI-297 (-7.5 Kcal/mol), GGTI-298 (-7.5 Kcal/mol), CHEMBL525185 (-7.2 Kcal/mol).