The kinase website displays the C lobe, N lobe and the activation loop. progression. Therefore, the development of FAK antagonists, as anti-cancer therapy, led to several small inhibitors of FAK kinase function that are currently undergoing clinical tests. Open in a separate window Number 1 The main structure domains of FAK. Important sites of tyrosine phosphorylation will also be indicated. Graphical network of FAK protein relationships recognized by BioGRID based on a compilation of publications referring to protein and genetic relationships. Circles with layers closest to the centre are more highly connected. However, besides its kinase function, FAK possess also scaffolding functions that are highly relevant in malignancy signalling [33]. Indeed, according to the Biological General Repository for Connection Datasets (BioGRID) [34,35], FAK is definitely involved in none of them less than 235 relationships. Nevertheless, some of these relationships are redundant because they were Dig2 characterized via different methods and by different laboratories. For example, Paxillin both interacts with the FAT website of FAK and is a substrate for its kinase activity. Therefore, the total quantity of unique FAK relationships identified until now is rather 125 (Number 1). The BioGRID data foundation considers as an connection any direct physical binding of two proteins, co-existence in a stable complex and genetic interaction. Therefore, the term interaction does not necessary involve a physical connection between two proteins as these relationships are recorded using various techniques including affinity capture-MS, affinity capture-Western, biochemical activity, co-fractionation, Novaluron co-purification, FRET or two-hybrid. For example, the affinity capture method identifies an interaction when a protein is definitely affinity captured from cell components by an antibody and the connected partner recognized either by mass spectroscopy or by European blot. Therefore, for FAK, some relationships were identified from the two-hybrid system while many others were characterized by the affinity capture-Western method and therefore may also be indirect as part of a signalling complex. Interactions recognized by high-throughput two-hybrid systems need to be further characterized in order to establish their biological effect on a defined system and thus will not be fully addressed with this study. With this review, we will rather focus on direct FAK relationships with a particular interest for those involved in tumor initiation and progression. These relationships and their effects on FAK activation and signalling will become described in details and we will examine how the knowledge of the structural motifs involved in these relationships could be the basis for development of PPI inhibitors. 3. FAK Structural Determinant for the Search of Potent FAK Inhibitors 3.1. Major Interactions in the FERM Website 3.1.1. FAK Connection with Growth Element Receptors and Mechanism of FAK Activation The best characterized mechanism that promotes FAK activation entails Integrin receptor clustering upon cell binding to the extracellular matrix which has been shown to involve binding of the Integrin cytoplasmic website to FAK [27,36,37]. Further analysis of Integrin-FAK relationships revealed the cytoplasmic tail of the 1 Integrin directly stimulates FAK activity in vitro, this activity becoming improved after Novaluron deletion of the FERM website of FAK suggesting a mechanism of FAK autoinhibition [38]. Recently, the 4 Integrin-FAK connection was mapped to 11-amino-acid region ahead of the FAK Tyr397 site [39]. FERM domains usually promote the coupling of cytoskeletal constructions to the plasma membrane. In the case of FAK, recent studies have shown that the rules of FAK activity entails an Novaluron intramolecular association of the FERM website with the kinase website, which then blocks the convenience of the Tyr397, the autophosphorylation site. Indeed, the crystal Novaluron structure of a FAK fragment comprising the FERM website and the kinase website in its auto-inhibited form reveals that this interaction requires the F2 lobe of the FERM website notably the residues Y180 and M183 and the c-lobe of the kinase website centred on F596 [40]. This mechanism of action implies that lipid-protein and/or protein-protein relationships in the FERM website are necessary to release the FERM-kinase connection (Number 2). Therefore, many components able to induce FERM-kinase website opening have been proposed which include Phosphatidylinositol-4,5-bisphosphate (PtdIns (4,5) P2 [41] the tetraspanin TM4SF5 [42] and growth element receptors. Among the second option both PDGFR, EGFR, IGF-1R, c-Met and RET were shown to form a complex with the FERM website of FAK [31,43,44,45], therefore.