Nonidentical subunits of p21H-ras farnesyltransferase. Peptide binding and farnesyl pyrophosphate carrier functions |
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Authors: | Y Reiss M C Seabra S A Armstrong C A Slaughter J L Goldstein M S Brown |
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Institution: | Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas 75235. |
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Abstract: | The protein farnesyltransferase purified from rat brain contains two nonidentical subunits, alpha and beta. The holoenzyme forms a stable complex with 3H]farnesyl pyrophosphate (FPP) that can be isolated by gel filtration. The 3H]FPP is not covalently bound to the enzyme; it is released unaltered when the enzyme is denatured. When incubated with an acceptor such as p21H-ras, the complex transfers 3H]farnesyl from the bound 3H]FPP to the ras protein. This transfer is not sensitive to dilution by unbound FPP, suggesting that the 3H]FPP is bound at a site that leads to direct transfer to the p21H-ras acceptor. Cross-linking studies show that the p21H-ras binds to the lower molecular weight subunit (beta-subunit), raising the possibility that the 3H]FPP binds to the alpha-subunit. If this suggestion can be confirmed, it would invoke a reaction mechanism in which the alpha-subunit acts as a prenyl pyrophosphate carrier that delivers FPP to p21H-ras which is bound to the beta-subunit. |
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