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Molecular docking programs successfully predict the binding of a beta-lactamase inhibitory protein to TEM-1 beta-lactamase.

Crystallization of the 1:1 molecular complex between the beta-lactamase TEM-1 and the beta-lactamase inhibitory protein BLIP has provided an opportunity to put a stringent test on current protein-docking algorithms. Prior to the successful determination of the structure of the complex, nine laboratory groups were given the refined atomic coordinates of each of the native molecules. Other than the fact that BLIP is an effective inhibitor of a number of beta-lactamase enzymes (KI for TEM-1 approximately 100 pM) no other biochemical or structural data were available to assist the practitioners in their molecular docking. In addition, it was not known whether the molecules underwent conformational changes upon association or whether the inhibition was competitive or non-competitive. All six of the groups that accepted the challenge correctly predicted the general mode of association of BLIP and TEM-1.

Amino Acid Sequence↗

Gab1 coupling to the HGF/Met receptor multifunctional docking site requires binding of Grb2 and correlates with the transforming potential.

Activation of the HGF receptor, encoded by the c-MET protooncogene (Met receptor), triggers motility, matrix-invasion and branching morphogenesis in epithelial cells. It has recently been shown that the Met receptor interacts with Gab-1, an IRS-like adaptor protein, via the docking site (Y1349VHVNATY1356VNV) known to bind Grb2 and multiple SH2-containing signal transducers. Here we show that Gab1 is the major phosphorylation-substrate of the Met receptor and of its oncogenic variant Tpr-Met. A series of point mutations in the docking site established a direct correlation between the ability to recruit and phosphorylate Gab1 and the transforming potential. Interestingly, the mutations of either Y1356 or N1358 abolished the binding of both Grb2 and Gab1 in intact cells. Furthermore, peptides designed to block either the SH2 or the SH3 domains of Grb2 interfered with the receptor-Gab1 interaction. These data indicate that Gab1 coupling to the Met receptor requires binding of Grb2 and correlates with the transforming potential of Tpr-Met.

Adaptor Proteins, Signal Transducing↗

The Ron oncogenic activity induced by the MEN2B-like substitution overcomes the requirement for the multifunctional docking site.

Oncogenic activation of the Ron tyrosine kinase (Macrophage Stimulating Protein receptor) relies on substitutions of two highly conserved residues in the catalytic domain (D1232V and M1254T), which result in ligand-independent activation of the receptor, in vivo tumorigenesis and metastasis. We show here that the Y/F conversion of the Y1317 residue in the kinase domain impairs tumorigenic and metastatic properties of Ron activated by the MEN2B-like mutation (RonM1254T), but not by other two oncogenic substitutions. Furthermore, RonM1254T lacking the multifunctional docking site retains transforming and metastatic activity. These data reveal that the transforming activity of RonM1254T mutant is dependent on Y1317 phosphorylation, suggesting a shift in intramolecular substrate specificity. Consistently, a shift of RonM1254T kinase substrate specificity was observed by in vitro peptide phosphorylation assays and in vivo receptor auto-phosphorylation. The Y1317 phosphorylation elicits by itself activation of PI-3K/Akt and MAPK signalling pathways. Our data indicate that the accomplishment of the full oncogenic phenotype of RonM1254T requires the phosphorylation both of the canonical C-terminal docking site and of the unique Y1317 residue in the tyrosine kinase domain.

Cell Transformation, Neoplastic↗

The docking protein Gab2 is overexpressed and estrogen regulated in human breast cancer.

Grb2-associated binder 2 (Gab2) is a recently identified member of the Gab/Daughter of sevenless family of docking proteins, which localize, amplify and integrate signaling pathways activated by various receptors including receptor tyrosine kinases (RTKs). To date, Gab2 signaling has been primarily investigated in hematopoietic cells. Here we report marked overexpression of Gab2 in a subset of breast cancer cell lines relative to normal breast epithelial strains and a trend for increased Gab2 expression in estrogen receptor (ER)-positive lines. Overexpression relative to normal ductal epithelium was also observed in some primary breast cancers. In MCF-7 breast cancer cells Gab2 was markedly tyrosine phosphorylated in response to heregulin and also following EGF, insulin or bFGF administration, indicating that a variety of RTKs implicated in breast cancer development or progression couple to this docking protein. In hormone-responsive breast cancer cells, GAB2 mRNA and protein expression were induced by estradiol in a manner sensitive to the pure anti-estrogen ICI 182780, indicating that this regulation is mediated via the ER. Gab2 therefore represents a novel link between steroid and growth factor signaling in breast cancer, and when overexpressed, may modulate the sensitivity of breast cancer cells to these important growth regulators.

Adaptor Proteins, Signal Transducing↗

On the rational design of substrate mimetics: The function of docking approaches for the prediction of protease specificities.

The behaviour of substrate mimetics in mediating the acceptance of nonspecific acyl moieties by proteases has been investigated as a direct function of their site-specific ester leaving groups. In this contribution we report on a computational approach to rationalise this interplay and to predict the power of a potential ester moiety to act as a suitable substrate mimetic for a given enzyme by means of an automated docking procedure. Investigations with seven distinct substrate mimetics and two proteases, subtilisin and chymotrypsin, show a clear correlation between the theoretically calculated binding energies DeltaE and the specificity constants k(cat)KM(-1) obtained from parallel hydrolysis kinetic studies. These results prove the general function of the docking approach as a rational model not only in predicting the general acceptance of a substrate mimetic in a qualitative manner, but also to provide reliable information on its individual specificity towards proteases.

Alanine↗

Cobatoxin 1 from Centruroides noxius scorpion venom: chemical synthesis, three-dimensional structure in solution, pharmacology and docking on K+ channels.

CoTX1 (cobatoxin 1) is a 32-residue toxin with three disulphide bridges that has been isolated from the venom of the Mexican scorpion Centruroides noxius Hoffmann. Here we report the chemical synthesis, disulphide bridge organization, 3-D (three-dimensional) solution structure determination, pharmacology on K+ channel subtypes (voltage-gated and Ca2+-activated) and docking-simulation experiments. An enzyme-based cleavage of the synthetic folded/oxidized CoTX1 indicated half-cystine pairs between Cys3-Cys22, Cys8-Cys27 and Cys12-Cys29. The 3-D structure of CoTX1 (solved by 1H-NMR) showed that it folds according to the common alpha/beta scaffold of scorpion toxins. In vivo, CoTX1 was lethal after intracerebroventricular injection to mice (LD50 value of 0.5 microg/mouse). In vitro, CoTX1 tested on cells expressing various voltage-gated or Ca2+-activated (IKCa1) K+ channels showed potent inhibition of currents from rat K(v)1.2 ( K(d) value of 27 nM). CoTX1 also weakly competed with 125I-labelled apamin for binding to SKCa channels (small-conductance Ca2+-activated K+ channels) on rat brain synaptosomes (IC50 value of 7.2 microM). The 3-D structure of CoTX1 was used in docking experiments which suggests a key role of Arg6 or Lys10, Arg14, Arg18, Lys21 (dyad), Ile23, Asn24, Lys28 and Tyr30 (dyad) residues of CoTX1 in its interaction with the rat K(v)1.2 channel. In addition, a [Pro7,Gln9]-CoTX1 analogue (ACoTX1) was synthesized. The two residue replacements were selected aiming to restore the RPCQ motif in order to increase peptide affinity towards SKCa channels, and to alter the CoTX1 dipole moment such that it is expected to decrease peptide activity on K(v) channels. Unexpectedly, ACoTX1 exhibited an activity similar to that of CoTX1 towards SKCa channels, while it was markedly more potent on IKCa1 and several voltage-gated K+ channels.

Amino Acid Sequence↗

Insulin stimulates the tyrosine dephosphorylation of docking protein p130cas (Crk-associated substrate), promoting the switch of the adaptor protein crk from p130cas to newly phosphorylated insulin receptor substrate-1.

The docking protein p130(cas) (Crk-associated substrate) forms a stable complex with the adaptor protein CrkII in a tyrosine-phosphorylation-dependent manner. Insulin-induced tyrosine phosphorylation of insulin receptor substrates results in the redistribution of CrkII between p130(cas) and insulin receptor substrate-1. A decrease in the association between CrkII and p130(cas) in response to insulin stimulation was detected in CHO cells stably expressing insulin receptor or insulin receptor substrate-1, and in L6 rat myoblasts. Along with the decrease in the association of CrkII with p130(cas), the amount of tyrosine-phosphorylated insulin receptor substrate-1 co-precipitated with CrkII increased in all cell types studied. The insulin-induced decrease in the CrkII-p130(cas) association was further confirmed by Far Western Blot analysis with the Src homology 2 (SH2) domain of CrkII. Insulin regulates the association of CrkII with p130(cas) by tyrosine dephosphorylation of p130(cas) and co-ordinated tyrosine phosphorylation of insulin receptor substrate-1. Tyrosine-phosphorylated insulin receptor substrate-1 serves as a docking protein for multiple adaptor proteins and competes with p130(cas) for CrkII.

Animals↗

Rab27 and its effectors in secretory granule exocytosis: a novel docking machinery composed of a Rab27.effector complex.

A small GTPase Rab27 is present on secretory granules in a wide variety of secretory cells and on melanosomes in melanocytes, and it is involved in controlling the trafficking of these organelles through interaction with a cell-type- or tissue-specific Rab27 effector(s). Slps (synaptotagmin-like proteins) and rabphilin contain an N-terminal Rab27-binding domain and C-terminal tandem C2 domains, and some of the Rab27-binding proteins have recently been shown to promote docking of Rab27-bound organelles to the plasma membrane. This mini-review presents a model for how the Rab27.effector complex controls the docking step in the trafficking of Rab27-bound organelles. Our results indicate that Slp2-a, Slp4-a/granuphilin-a and rabphilin are capable of interacting with the plasma membrane directly or indirectly, and thus that these Rab27 effectors form a bridge between Rab27-bound organelles and the plasma membrane.

Animals↗

Effects of acute pain reduction methods on the chronic inflammatory lesions and behaviour of lambs castrated and tail docked with rubber rings at less than two days of age.

Lesions were produced by castration and tail docking of two-day-old Dorset-cross lambs with elastrator rings with (RRla) and without (RR) local anaesthetic or after destruction of the innervation by crushing close to the ring (Brr). The lesions were monitored twice weekly for six weeks and the behaviour of handled controls (H), RR and RRla lambs was recorded for two 3 h periods 10, 20, 31 and 41 days after treatment. There was no significant effect of castration and tail docking, with or without pain reduction methods, on daily liveweight gain. In the Brr lambs, the dead tails were cast 10 days earlier than from RR and RRla lambs. The time taken for the scrotal lesion to reach maximum severity was halved in Brr and RRla lambs, although the maximum severity of the lesion was unaffected by the methods of pain reduction. During the four 6 h behavioural observation periods, RR lambs showed a significant increase in the mean (+/- sd) frequency of foot stamping (RR13 +/- 13; H2 +/- 2.5), tail wagging (61 +/- 26; 15 +/- 6), head turning to the scrotum and inside hind-leg (12 +/- 10; 1 +/- 1). Less abnormal behaviour was found after RRla than after RR treatment. This unexpected finding may be evidence of long-lasting increases in pain sensitivity after an episode of intense acute pain in young animals.

Animal Welfare↗

Synthesis and docking studies of alkylene-linked dimers of (-)-huperzine A.

(-)-Huperzine A (5, HupA), an alkaloid isolated from the herb Huperzia serrata, is a potent, selective and reversible acetylcholinesterase (AchE) inhibitor. Based on the hypothesis with respect to two binding sites in the active gorge of AChE and the good example of bis-tacrine, it was predicted from the docking studies of alkylene-linked dimers of HupA that dimers 6 (n = 5, 7, 9) might have good AChE inhibitory activity. Therefore, six dimers with 7-12 methylene units as tethers were thus prepared. It was found that these dimers were less potent than HupA in inhibition of AChE. The difference of the inhibitory potency between these dimers is coincident with the results of the docking studies.

Alkaloids↗

Parallelized-over-parts computation of absolute binding free energy with docking and molecular dynamics.

We present a technique for biomolecular free energy calculations that exploits highly parallelized sampling to significantly reduce the time to results. The technique combines free energies for multiple, nonoverlapping configurational macrostates and is naturally suited to distributed computing. We describe a methodology that uses this technique with docking, molecular dynamics, and free energy perturbation to compute absolute free energies of binding quickly compared to previous methods. The method does not require a priori knowledge of the binding pose as long as the docking technique used can generate reasonable binding modes. We demonstrate the method on the protein FKBP12 and eight of its inhibitors.

Biophysics↗

Docking kinetics and equilibrium of a GAAA tetraloop-receptor motif probed by single-molecule FRET.

Docking kinetics and equilibrium of fluorescently labeled RNA molecules are studied with single-molecule FRET methods. Time-resolved FRET is used to monitor docking/undocking transitions for RNAs containing a single GAAA tetraloop-receptor tertiary interaction connected by a flexible single-stranded linker. The rate constants for docking and undocking are measured as a function of Mg2+, revealing a complex dependence on metal ion concentration. Despite the simplicity of this model system, conformational heterogeneity similar to that noted in more complex RNA systems is observed; relatively rapid docking/undocking transitions are detected for approximately two-thirds of the RNA molecules, with significant subpopulations exhibiting few or no transitions on the 10- to 30-s time scale for photobleaching. The rate constants are determined from analysis of probability densities, which allows a much wider range of time scales to be analyzed than standard histogram procedures. The data for the GAAA tetraloop receptor are compared with kinetic and equilibrium data for other RNA tertiary interactions.

Base Sequence↗

Computational docking and solution x-ray scattering predict a membrane-interacting role for the histone domain of the Ras activator son of sevenless.

The Ras-specific nucleotide exchange factor son of sevenless (SOS) is a large, multidomain protein with complex regulation, including a Ras-dependent allosteric mechanism. The N-terminal segment of SOS, the histone domain, contains two histone folds, which is highly unusual for a cytoplasmic protein. Using a combination of computational docking, small-angle x-ray scattering, mutagenesis, and calorimetry, we show that the histone domain folds into the rest of SOS and docks onto a helical linker that connects the pleckstrin-homology (PH) and Dbl-homology (DH) domains of SOS to the catalytic domain. In this model, a positively charged surface region on the histone domain is positioned so as to provide a fourth potential anchorage site on the membrane for SOS in addition to the PH domain, the allosteric Ras molecule, and the C-terminal adapter-binding site. The histone domain in SOS interacts with the helical linker, using a region of the surface that in nucleosomes is involved in histone tetramerization. Adjacent surface elements on the histone domain that correspond to the DNA-binding surface of nucleosomes form the predicted interaction site with the membrane. The orientation and position of the histone domain in the SOS model implicates it as a potential mediator of membrane-dependent activation signals.

Allosteric Regulation↗

Stably tethered multifunctional structures of defined composition made by the dock and lock method for use in cancer targeting.

We describe a platform technology, termed the dock and lock method, which uses a natural binding between the regulatory subunits of cAMP-dependent protein kinase and the anchoring domains of A kinase anchor proteins for general application in constructing bioactive conjugates of different protein and nonprotein molecules from modular subunits on demand. This approach could allow quantitative and site-specific coupling of many different biological substances for diverse medical applications. The dock and lock method is validated herein by producing bispecific, trivalent-binding complexes composed of three stably linked Fab fragments capable of selective delivery of radiotracers to human cancer xenografts, resulting in rapid, significantly improved cancer targeting and imaging, providing tumor/blood ratios from 66 +/- 5 at 1 h to 395 +/- 26 at 24 h.

Amino Acid Sequence↗

Stimulation of phosphatidylinositol 3-kinase by fibroblast growth factor receptors is mediated by coordinated recruitment of multiple docking proteins.

The docking protein FRS2 is a major downstream effector that links fibroblast growth factor (FGF) and nerve growth factor receptors with the Ras/mitogen-activated protein kinase signaling cascade. In this report, we demonstrate that FRS2 also plays a pivotal role in FGF-induced recruitment and activation of phosphatidylinositol 3-kinase (PI3-kinase). We demonstrate that tyrosine phosphorylation of FRS2alpha leads to Grb2-mediated complex formation with the docking protein Gab1 and its tyrosine phosphorylation, resulting in the recruitment and activation of PI3-kinase. Furthermore, Grb2 bound to tyrosine-phosphorylated FRS2 through its SH2 domain interacts primarily via its carboxyl-terminal SH3 domain with a proline-rich region in Gab1 and via its amino-terminal SH3 domain with the nucleotide exchange factor Sos1. Assembly of FRS2alpha:Grb2:Gab1 complex induced by FGF stimulation results in activation of PI3-kinase and downstream effector proteins such as the S/T kinase Akt, whose cellular localization and activity are regulated by products of PI3-kinase. These experiments reveal a unique mechanism for generation of signal diversity by growth factor-induced coordinated assembly of a multidocking protein complex that can activate the Ras/mitogen-activated protein kinase cascade to induce cell proliferation and differentiation, and PI3-kinase to activate a mediator of a cell survival pathway.

3T3 Cells↗

Critical role for the docking-protein FRS2 alpha in FGF receptor-mediated signal transduction pathways.

The docking protein FRS2 alpha has been implicated as a mediator of signaling via fibroblast growth factor receptors (FGFRs). We have demonstrated that targeted disruption of FRS2 alpha gene causes severe impairment in mouse development resulting in embryonal lethality at E7.0--E7.5. Experiments with FRS2 alpha-deficient fibroblasts demonstrate that FRS2 alpha plays a critical role in FGF-induced mitogen-activated protein (MAP) kinase stimulation, phosphatidylinositol-3 (PI-3) kinase activation, chemotactic response, and cell proliferation. Following FGF stimulation, tyrosine phosphorylated FRS2 alpha functions as a site for coordinated assembly of a multiprotein complex that includes Gab1 and the effector proteins that are recruited by this docking protein. Furthermore, we demonstrate that different tyrosine phosphorylation sites on FRS2 alpha are responsible for mediating different FGF-induced biological responses. These experiments establish the central role of FRS2 alpha in signaling via FGFRs and demonstrate that FRS2 alpha mediates multiple FGFR-dependent signaling pathways critical for embryonic development.

Adaptor Proteins, Signal Transducing↗

Structure of tRNA pseudouridine synthase TruB and its RNA complex: RNA recognition through a combination of rigid docking and induced fit.

RNA pseudouridine synthase, TruB, catalyzes pseudouridine formation at U55 in tRNA. This posttranscriptional modification is almost universally conserved and occurs in the T arm of most tRNAs. We determined the crystal structure of Escherichia coli TruB apo enzyme, as well as the structure of Thermotoga maritima TruB in complex with RNA. Comparison of the RNA-free and -bound forms of TruB reveals that this enzyme undergoes significant conformational changes on binding to its substrate. These conformational changes include the ordering of the "thumb loop," which binds right into the RNA hairpin loop, and a 10 degree hinge movement of the C-terminal domain. Along with the result of docking experiments performed on apo TruB, we conclude that TruB recognizes its RNA substrate through a combination of rigid docking and induced fit, with TruB first rigidly binding to its target and then maximizing the interaction by induced fit.

Binding Sites↗

Identification of a protein complex that is required for nuclear protein import and mediates docking of import substrate to distinct nucleoporins.

We have identified and characterized a 9S protein complex from a Xenopus ovary cytosolic subfraction (fraction A) that constitutes this fraction's activity in recognizing a model nuclear import substrate and docking it at the nuclear pore complex. Because of its function, the complex is termed karyopherin. The 54- and 56-kDa subunits of the complex are termed alpha 1 and alpha 2, respectively, and the 97-kDa subunit is termed beta. In an alternative approach we have identified karyopherin beta from a rat liver cytosolic subfraction A by using immobilized rat nucleoporin Nup98 in a single, affinity-based enrichment step. We have molecularly cloned and sequenced rat karyopherin beta. Comparison with protein sequence data banks showed no significant similarity to other known proteins. Using nitrocellulose-immobilized rat liver nuclear envelope proteins and nuclear import substrate as a ligand, we found Xenopus fraction A-dependent binding to at least three bona fide nucleoporins (Nup214, Nup153, and Nup98) and to a candidate nucleoporin with an estimated molecular mass of 270 kDa. We propose that these nucleoporins function as docking proteins for karyopherin-mediated binding of substrate in a nuclear import/export pathway across the nuclear pore complex.

Amino Acid Sequence↗