This combination of structural and thermodynamic information could be used to assist rational drug design of therapeutics directed towards disrupting the RalB-RLIP76 complex

This combination of structural and thermodynamic information could be used to assist rational drug design of therapeutics directed towards disrupting the RalB-RLIP76 complex. == Results and Discussion == == Structure of the RLIP76 GBD == The quality of the NMR data of wild-type RLIP76 GBD protein, comprising residues 393-446, suggested that the domain was partially dimerized in solution and this was confirmed by analytical gel filtration experiments. RLIP76 bind Ral proteins competitively and with similar affinitiesin vitro. == Introduction == Cell migration is a normal, essential process but in cancer progression it is the LAMP1 antibody basis for the ability of tumour cells to metastasize to new areas of the body, a process that leads to 90% of cancer deaths (Sporn, 1996). Approximately 50% of metastatic tumours contain mutations in the small G protein Ras and one of the three main effector pathways downstream of Ras is controlled by RalGEFs, which are exchange factors (and therefore activators) for another pair of small G proteins, RalA and RalB. Cells transformed with either an activated Ras variant (12V, 37G) that only interacts with the RalGEFs or with constitutively Flecainide acetate active RalGEF produced aggressive, infiltrative metastases when injected into mice. These were inhibited by dominant negative RalB (Ward et al., 2001), demonstrating that the RalGEF pathway alone is sufficient to induce a metastatic phenotype. In bladder cancer lines, EGF stimulation activates Ral and elevated levels of activated Ral are confined to metastatic cells (Gildea et al., 2002). It is therefore clear that the Ral pathway represents a potential target for the treatment of human metastatic cancers. The Ral signalling pathway(s) responsible for conferring metastatic potential on cancer cells is less well defined. The effectors for the Ral GTPases regulate a wide variety of cellular functions and include phospholipase D (Jiang et al., 1995), the actin filament crosslinking protein filamin A (Ohta et al., 1999), the Y-box transcription factor ZONAB (ZO-1 associated nucleic acid binding protein) (Frankel et al., 2005), phospholipase C 1 (Sidhu et al., 2005), two components of the exocyst complex, Sec5 and Exo84, (Moskalenko et al., 2002), (Sugihara et al., Flecainide acetate 2002), (Moskalenko et al., 2003) and RLIP76 (RalBP1/RIP1) (Jullien-Flores et al., 1995), (Cantor et al., 1995), (Park and Weinberg, 1995). RLIP76 is a multifunctional protein, containing a variety of domains and motifs (Figure 1A). Its RhoGAP domain acts on Rac1 and Cdc42, linking Ral with Rho family signalling (Jullien-Flores et al., 1995), (Cantor et al., 1995), (Park and Weinberg, 1995) and therefore control of the actin cytoskeleton and cell motility. RLIP76 is also involved in endocytosis and tyrosine kinase receptor signalling via its ability to bind to AP2 and POB1 through its N-terminal and C-terminal regions respectively (Yamaguchi et al., 1997), (Jullien-Flores et al., 2000). == Figure 1. Structures of RLIP76 GBD alone and in complex with RalB. == A. Domain structure of RLIP76. The approximate positions of the RhoGAP domain, the Ral binding domain (GBD) and coiled-coil region are represented as coloured boxes, the regions found to interact with AP2 and POB1 are indicated and the locations of the putative ATP binding sites are marked with red arrows (Awasthi et al., 2001). B. Structure of free RLIP76 GBD. On the left is the backbone trace Flecainide acetate of the family of structures consistent with the NMR restraints, on the right is the closest structure to the mean. All structure figures were produced using Molscript (Kraulis, 1991) and rendered with Raster3D (Merritt and Bacon, 1997). C. Structure of the RLIP76 GBD-RalB complex. Ral is shown in blue and RLIP76 is lilac. On the left is the backbone trace of the lowest energy structures, on the right is the closest structure to the mean. Although RLIP76 is thought to be primarily cytosolic it translocates to the membrane upon binding by Ral. RLIP76 contains two ATP binding sites (Awasthi et al., 2001), which allow it to function as.