H-Ras protein

The central unit of these peptidomimetics imitates a /1-turn and brings the NH2-terminus of the cysteine analogue and the CO OH terminus of the methionine in spatial proximity these can then complex the Zn2+ ion which is essential for activity of the FTase [26]. The free acid 7 inhibits the enzyme with an IC50 value of 1 nmol/1, whilst in intact cells the methyl ester 8, despite its weaker in vitro activity, is significantly more potent because it can penetrate the plasma membrane better due to its lower polarity. This property can be used to convert the morphology of H-Ras-transformed cells back to the normal form and to inhibit growth of these cells, whereas the substance shows no effect on Src-transformed and untransformed rat fibroblasts. The inhibitor therefore acts selectively on transformed cells and does not influence growth of normal cells. This result is noteworthy because farnesylation of the wild type H-Ras protein... 

Lipid modified proteins are often attached to cell membranes. In many cases, they play crucial roles in the transduction of extracellular signals across the plasma membrane and into the nucleus. A particularly important example are the N-, K-, and H-Ras proteins. All Ras proteins terminate in a fame... 

For MIC ligations truncated H-Ras protein with a C-terminal cysteine at the position 181 was recombi-nantly expressed in E. coli. The removal of the last eight C-terminal amino acids (MSCKCVLS) had no effect on... 

Palmitoylation is, after myristoylation, the most common modification of the a-sub-rmit of the heterotrimeric G-proteins (see chapter 5). The a-subunit of G-proteins can be lipidated in a two-fold marmer, with a myristoic acid and a pahnitoic acid anchor at the N-terminus. It appears in this case that two lipid anchors are necessary to mediate a stable association of the protein with the membrane. The lipidation of cytoplasmic protein tyrosine kinase also includes both myristoylation and palmitoylation. H-Ras protein also requires, apart from C-terminal farnesylation (see below), a pahnitoyl modification in order to bind to the plasma membrane. In all mentioned examples the fatty acid anchors play an essential role in the signal transduction. 

Scheme 2. Thioether-forming ligation of the li popeptide 2 to the truncated H-Ras protein 1. 

We used this library to find receptors for the CaaX-box of the H-RAS protein. Because selecting molecular forceps from libraries for H-RAS binding does not ensure these forceps will recognize the carboxy terminus of H-RAS, however, we decided to take a two-pronged screening approach - in addition to screening the library with the protein, we sought to screen with the isolated carboxy-terminal peptide from H-RAS to select molecular forceps that bind this epitope specifically. 

The re-synthesized molecular forceps (MF1 through MF8, except MF5 which was not soluble) were tested for inhibition of farnesylation by yeast FTase [25], As expected, MF8, our negative selection, did not inhibit farnesylation of H-RAS protein. MF6 and MF7 from the protein screening also had no effect neither did MF1 that we had obtained from peptide screening. MF4 had a weak impact on the far-... 

Inhibition of protein geranylgeranylation in NIH3T3 cells was demonstrated by the appearance of unprenylated form of Rapl using an antibody specific for unprenylated Rapl. On the other hand, P61-A6 did not inhibit protein farnesylation as examined by the mobility shift of H-Ras protein on a SDS polyacrylamide gel. Similarly, P61-A6 did not inhibit geranylgeranylation of Rab5b catalyzed by RabGGTase. 

Zhang, J., and Matthews, C.R. (1998) The role of ligand binding in the kinetic folding mechanism of human p21(H-ras) protein. Biochemistry 37, 14891-9. 

Non-SELEX Aptamers for h-Ras protein were selected through... 

Figure 9.9 Non-SELEX selection of aptamers for h-Ras protein (A) procednre for selection and accompanying analyses of pools (B) results of NECEEM binding analyses of pools after each of the three steps of Non-SELEX.

H-ras proteins, the products of the ras onco- and protooncogenes, are guanine nucleotide binding proteins, which act as molecular switch. In the active state, liras proteins are bound to guanosine triphosphate (GTP), and in order to switch to the inactive state, the y-phosphate of the nucleotide has to be hydrolyzed. In the oncogenic mutation, this reaction is suppressed. Understanding this reaction is very important to overcome human cancer, because H-ras proteins frequently mutate to be activated in a variety of human cancer cells [1]. 

So far, NECEEM was used to study the interaction between several proteins and DNA such as an Escherichia coli single-stranded DNA-binding protein (SSB) and a fluorescently labeled oligonucleotide (ssDNA), Taq DNA polymerase and its aptamer, thrombin and its aptamer, Tau protein and single-stranded and double-stranded DNA, protein farnesyltransferase (PFTase) and its aptamer, MutS protein and its aptamer, h-Ras protein and its aptamer, and Mef2c protein and double-stranded DNA it naturally binds. It has also been used to study protein-peptide interactions. ... 

Because Ras proteins are farnesylated in the cytosol, then targeted to the endoplasmic reticulum for subsequent processing, and, if required, directed to the Golgi for palmitoylation before their ultimate signaling destination, the question arises how the specific distribution of these proteins is maintained. Traffic by vesicles or diffusion processes were proposed for N- and H-Ras proteins, and the involvement of transport proteins has been suggested for K-Ras. However, the factors regulating the transport or distribution of Ras proteins over the different cellular membranes are still poorly understood, mainly due to the lack of appropriate tools enabling this study. 

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