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Original

Membrane interactions of peptides representing the polybasic regions of three Rho GTPases are sensitive to the distribution of arginine and lysine residues

, , , &
Pages 14-22 | Received 24 Jan 2007, Published online: 09 Jul 2009
 

Abstract

Rho GTPases are a multifunctional family of proteins that are localized at cellular membranes via an isoprenyl group covalently linked to a C-terminal cysteine. Close to this primary site of membrane anchoring there is often found an additional polybasic region (PBR), which plays a secondary role in membrane binding and targeting of the complex. Here, peptides derived from the PBRs of the Rho family proteins Rac1 (K183KRKRK), TCL (K198KKKKR) and Cdc42 (P182KKSRR) were prepared with hexalysine (K6) and hexaarginine (R6) to study their interactions with multilamellar vesicles of phosphatidylglycerol (DOPG) and headgroup-deuterated dimyristoylphosphatidylcholine (DMPC-d4) using 2H and 31P NMR. The membranes retained their lamellar architecture after peptide binding, but the 2H NMR line shapes for DMPC-d4 indicated that the bound peptides altered the orientation of the choline headgroups, consistent with a change in membrane surface charge. Rac1 and TCL peptides appeared to affect the headgroup orientation similarly to K6, although the perturbations were weaker and unlike those induced by the Cdc42 peptide and R6. Magic-angle spinning 31P NMR spectra of the membranes showed significant and selective broadening of the peak for DMPC after addition of the peptides, with R6 and the Cdc42 peptide having the greatest effect. The selective broadening may be a consequence of the lipids separating into short-lived domains enriched in peptide-bound DOPG and peptide-free DMPC. These results illustrate that a complex relationship exists between the sequence of PBRs and their behaviour at membrane surfaces, which may have implications for the cellular functions and localization of Rho GTPases.

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