FAK dimerization controls its kinase-dependent functions at focal adhesions.

Focal adhesion kinase (FAK) controls adhesion-dependent cell motility, survival, and proliferation. FAK has kinase-dependent and kinase-independent functions, both of which play major roles in embryogenesis and tumor invasiveness. The precise mechanisms of FAK activation are not known. Using x-ray crystallography, small angle x-ray scattering, and biochemical and functional analyses, we show that the key step for activation of FAK's kinase-dependent functions--autophosphorylation of tyrosine-397--requires site-specific dimerization of FAK. The dimers form via the association of the N-terminal FERM domain of FAK and are stabilized by an interaction between FERM and the C-terminal FAT domain. FAT binds to a basic motif on FERM that regulates co-activation and nuclear localization. FAK dimerization requires local enrichment, which occurs specifically at focal adhesions. Paxillin plays a dual role, by recruiting FAK to focal adhesions and by reinforcing the FAT:FERM interaction. Our results provide a structural and mechanistic framework to explain how FAK combines multiple stimuli into a site-specific function. The dimer interfaces we describe are promising targets for blocking FAK activation.

The emergence of the Responsible Conduct of Research (RCR) in PHS policy and practice.

The Responsible Conduct of Research (RCR) is now an established academic field taught at virtually every major American research university and generates a growing volume of research and pedagogical literature. Paradoxically, it is a field without a consensually agreed upon definition, goals, foundational theories, research agenda, and pedagogical methodology. It has been suggested that RCR as currently being taught is ineffective in preventing misconduct and improving the quality of research. The following short history of RCR, focused mainly on Federal policy and practice, explains how this curious state of affairs developed and persists and concludes with some suggestions for the future of RCR instruction.

Crystal structures of mutant forms of the yeast F1 ATPase reveal two modes of uncoupling.

The mitochondrial ATP synthase couples the flow of protons with the phosphorylation of ADP. A class of mutations, the mitochondrial genome integrity (mgi) mutations, has been shown to uncouple this process in the yeast mitochondrial ATP synthase. Four mutant forms of the yeast F(1) ATPase with mgi mutations were crystallized; the structures were solved and analyzed. The analysis identifies two mechanisms of structural uncoupling: one in which the empty catalytic site is altered and in doing so, apparently disrupts substrate (phosphate) binding, and a second where the steric hindrance predicted between γLeu83 and ß(DP) residues, Leu-391 and Glu-395, located in Catch 2 region, is reduced allowing rotation of the γ-subunit with less impedance. Overall, the structures provide key insights into the critical interactions in the yeast ATP synthase involved in the coupling process.

Structural insights into the association between BCAR3 and Cas family members, an atypical complex implicated in anti-oestrogen resistance.

The association between novel Src homology 2-containing protein (NSP) and Crk-associated substrate (Cas) family members contributes to integrin and receptor tyrosine kinase signalling and is involved in conferring anti-oestrogen resistance to human breast carcinomas. The precise role of this association in tumorigenesis remains controversial, and the molecular basis for the complex NSP and Cas protein form is unknown. Here we present a pluridisciplinary approach, including small-angle X-ray scattering, that provides first insights into the structure of the complex formed between breast cancer anti-oestrogen resistance 3 (BCAR3, an NSP family member) and human enhancer of filamentation 1 (HEF1, also named NEDD9 or Cas-L, a Cas family protein). Our analysis corroborates a four-helix bundle structure for the NSP-binding domain of HEF1 and a Cdc25-like guanine nucleotide exchange factor (GEF) fold for the Cas-binding domain of BCAR3. Using residues located on helix 2 of the four-helix bundle, HEF1 binds very tightly to a site on BCAR3 that is remote from the putative guanosine triphosphatase binding site of the GEF domain, but similar to a site implicated in allosteric regulation of the homologous SOS (Son of Sevenless) GEF domain. Thus, the association between NSP and Cas proteins might not only create a very stable link between these molecules, co-localising their cellular functions, but also modulate the function of the NSP GEF domains. Such modulation may explain, at least in part, the controversial results published for NSP GEF function.

Crystal structure of phosphoglucose isomerase from Trypanosoma brucei complexed with glucose-6-phosphate at 1.6 A resolution.

Enzymes of glycolysis in Trypanosoma brucei have been identified as potential drug targets for African sleeping sickness because glycolysis is the only source of ATP for the bloodstream form of this parasite. Several inhibitors were previously reported to bind preferentially to trypanosomal phosphoglucose isomerase (PGI, the second enzyme in glycolysis) than to mammalian PGIs, which suggests that PGI might make a good target for species-specific drug design. Herein, we report recombinant expression, purification, crystallization and X-ray crystal structure determination of T. brucei PGI. One structure solved at 1.6 A resolution contains a substrate, D-glucose-6-phosphate, in an extended conformation in the active site. A second structure solved at 1.9 A resolution contains a citrate molecule in the active site. The structures are compared with the crystal structures of PGI from humans and from Leishmania mexicana. The availability of recombinant tPGI and its first high-resolution crystal structures are initial steps in considering this enzyme as a potential drug target.

Conformational changes in phosphoglucose isomerase induced by ligand binding.

Phosphoglucose isomerase (PGI; EC 5.3.1.9) is the second enzyme in glycolysis, where it catalyzes the isomerization of D-glucose-6-phosphate to D-fructose-6-phosphate. It is the same protein as autocrine motility factor, differentiation and maturation mediator, and neuroleukin. Here, we report a new X-ray crystal structure of rabbit PGI (rPGI) without ligands bound in its active site. The structure was solved at 1.8A resolution by isomorphous phasing with a previously solved X-ray crystal structure of the rPGI dimer containing 6-phosphogluconate in its active site. Comparison of the new structure to previously reported structures enables identification of conformational changes that occur during binding of substrate or inhibitor molecules. Ligand binding causes an induced fit of regions containing amino acid residues 209-215, 245-259 and 385-389. This conformational change differs from the change previously reported to occur between the ring-opening and isomerization steps, in which the helix containing residues 513-521 moves toward the bound substrate. Differences between the liganded and unliganded structures are limited to the region within and close to the active-site pocket.

The crystal structure of rabbit phosphoglucose isomerase complexed with 5-phospho-D-arabinonohydroxamic acid.

Phosphoglucose isomerase (EC ) catalyzes the second step in glycolysis, the reversible isomerization of D-glucose 6-phosphate to D-fructose 6-phosphate. The reaction mechanism involves acid-base catalysis with proton transfer and proceeds through a cis-enediol(ate) intermediate. 5-Phospho-D-arabinonohydroxamic acid (5PAH) is a synthetic small molecule that resembles the reaction intermediate, differing only in that it has a nitrogen atom in place of C1. Hence, 5PAH is the best inhibitor of the isomerization reaction reported to date with a K(i) of 2 x 10(-7) M. Here we report the crystal structure of rabbit phosphoglucose isomerase complexed with 5PAH at 1.9 A resolution. The interaction of 5PAH with amino acid residues in the enzyme active site supports a model of the catalytic mechanism in which Glu-357 transfers a proton between C1 and C2 and Arg-272 helps stabilize the intermediate. It also suggests a mechanism for proton transfer between O1 and O2.