Defining the landscape of ATP-competitive inhibitor resistance residues in protein kinases.

Kinases are involved in disease development and modulation of their activity can be therapeutically beneficial. Drug-resistant mutant kinases are valuable tools in drug discovery efforts, but the prediction of mutants across the kinome is challenging. Here, we generate deep mutational scanning data to identify mutant mammalian kinases that drive resistance to clinically relevant inhibitors. We aggregate these data with subsaturation mutagenesis data and use it to develop, test and validate a framework to prospectively identify residues that mediate kinase activity and drug resistance across the kinome. We validate predicted resistance mutations in CDK4, CDK6, ERK2, EGFR and HER2. Capitalizing on a highly predictable residue, we generate resistance mutations in TBK1, CSNK2A1 and BRAF. Unexpectedly, we uncover a potentially generalizable activation site that mediates drug resistance and confirm its impact in BRAF, EGFR, HER2 and MEK1. We anticipate that the identification of these residues will enable the broad interrogation of the kinome and its inhibitors.

Primary structure of CHH/MIH/GIH-like peptides in sinus gland extracts from Penaeus vannamei.

Peptides belonging to the CHH/MIH/GIH-family of crustacean hormones were isolated from acetic acid extracts of sinus glands isolated from eyestalks of the shrimp, Penaeus vannamei. The peptides were isolated by chromatography and molecular weights determined by MALDI mass spectrometry. Peptides in the range of 7-9 kDa and containing three disulfide bridges were selected for amino acid sequence analysis. Three peptides with the requisite properties were present in sufficient amounts for sequence analysis. Two peptides had unique sequences similar to CHH/MIH/GIH peptides from other crustaceans. A third peptide seemed to be a truncated form of one of the previous sequences.

Dose-dependent effects of CRF-like diuretic peptide on transcellular and paracellular transport pathways.

The mechanism of action of synthetic Culex corticotropin-releasing factor (CRF)-like diuretic peptide (CCRF-DP) was investigated in isolated, perfused Malpighian tubules of the yellow fever mosquito, Aedes aegypti. Low concentrations of CCRF-DP (10(-10) and 10(-9) M) caused depolarizing oscillations of the lumen-positive transepithelial voltage (Vt) in Malpighian tubules, whereas high concentrations (10(-8) and 10(-7) M) first depolarized and then transiently hyperpolarized Vt; CCRF-DP always lowered transepithelial resistance (Rt), regardless of voltage depolarization or hyperpolarization. The short-circuit current (Isc), an electrical estimate of active transepithelial transport of Na and K, remained unchanged at low concentrations of CCRF-DP, but Isc more than doubled at high concentrations. These effects of CCRF-DP suggest dose-dependent sites of action: low concentrations of CCRF-DP affect the paracellular pathway, and high concentrations affect both paracellular and transcellular pathways.

The concentration-dependence of CRF-like diuretic peptide: mechanisms of action.

The mechanism of action of synthetic CCRF-DP, the corticotropin-releasing factor (CRF)-related diuretic peptide of the salt marsh mosquito Culex salinarius, was investigated in isolated Malpighian tubules of the yellow fever mosquito Aedes aegypti. A low concentration of CCRF-DP (10(-9)mol l-1) caused a small but insignificant increase in transepithelial secretion of NaCl and fluid, but significantly reduced transepithelial voltage and resistance without a change in short-circuit current, pointing to the stimulation of passive Cl- transport through the paracellular pathway as the principal mechanism of a mild diuresis. Significant changes in voltage and resistance but not in short-circuit current were duplicated by the ionophore A23187 (0.4 micromol l-1), suggesting Ca2+ as a second messenger at 10(-9)mol l-1 CCRF-DP. A high concentration of CCRF-DP (10(-7)mol l-1) significantly increased transepithelial secretion of NaCl and fluid and significantly increased short-circuit current, pointing to the stimulation of active Na+ transport through the transcellular pathway as the mechanism of a strong diuresis. This effect was mimicked by dibutyryl-cAMP, suggesting cAMP as a second messenger at 10(-7)mol l-1 CCRF-DP. Dibutyryl-cGMP had no effects. These results suggest dose-dependent, receptor-mediated effects of CCRF-DP that target discrete transport pathways via discrete second messengers: low concentrations of CCRF-DP cause a mild diuresis, apparently via Ca2+-mediated effects on paracellular Cl- transport, and high concentrations cause a strong diuresis via cAMP-mediated effects on active transcellular Na+ transport in addition to the effects on the paracellular pathway.

Isolation and immunocytochemical characterization of three tachykinin-related peptides from the mosquito, Culex salinarius.

Three myotropic peptides belonging to the Arg-amide insect tachykinin family were isolated from whole-body extracts of the mosquito, Culex salinarius. The peptides, APSGFMGMR-NH2, APYGFTGMR-NH2 and APSGFFGMR-NH2 (designated culetachykinin I, II, and III) were isolated and purified on the basis of their ability to stimulate muscle contractions of isolated Leucophaea maderae hindgut. Biologically inactive methionine sulfoxides of two of the three peptides were isolated using an ELISA system based upon antiserum raised against APYGFTGMR-NH2 and identified with mass spectrometry. Immunocytochemistry localized these peptides in cells in the brain, antennae, subesophageal, thoracic and abdominal ganglion, proventriculus and midgut. Nerve tracts containing these peptides were found in the median nerve of the brain, central body, nervi corpus cardiaci, cervical nerve, antennal lobe and on the surface of the midgut.

Inactivation of Dip-allatostatin 5 by membrane preparations from the cockroach Diploptera punctata.

Incubation of Dip-AST 5 (Asp-Arg-Leu-Tyr-Ser-Phe-Gly-Leu-NH2) with membrane preparations of midgut, hindgut, brain, or corpora allata (CA) results in its inactivation in terms of the inhibition of juvenile hormone biosynthesis. Dip-AST 5 is initially cleaved at Gly7-Leu8 to yield the N-terminal heptapeptide (Asp-Arg-Leu-Tyr-Ser-Phe-Gly). At supraphysiological concentration, the half-life of Dip-AST 5 varied from 24 min by membrane preparations of brain to approximately 53 min following incubation with midgut membrane preparations. At more physiological concentrations (nanomolar), Dip-AST 5 was still initially cleaved to yield the inactive N-terminal heptapeptide with a half-life ranging from 23 min with brain membrane preparations to 85 min with membrane preparations of midgut. The fact that Dip-AST 5 is rapidly degraded to an inactive product by membrane preparations or whole tissues (CA) indicates that Dip-AST 5 has a different metabolic fate in tissue preparations than in diluted hemolymph (Garside et al., 1997). These findings demonstrate that the degradation of allatostatins by tissue preparations of D. punctata may play an important role in the termination of their ability to inhibit juvenile hormone biosynthesis by the CA and/or to modulate muscle activity in the hindgut.

MALDI-MS as a monitor of the purification and folding of synthetic eclosion hormone.

Analogues of the small protein Manduca sexta eclosion hormone (62 amino acids) were synthesized by Fmoc solid-phase methodology. Matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) was used to analyze the products of the syntheses and this information was used to design an efficient purification scheme. MALDI-MS was used to monitor the target products through purification and it was also used to monitor folding of the purified materials. The folded EH analogues were shown to be biologically active proteins with an in vivo bioassay using pharate adult moths, Heliothis virescens.

Degradation of Dip-allatostatins by hemolymph from the cockroach, Diploptera punctata.

Incubation of Dip-AST 7 (APSGAQRLYGFGLa) or Dip-AST 9 (GDGRLYAFGLa) (5 microM) with hemolymph for 30 min results in cleavage by a putative endopeptidase, yielding the C-terminal hexapeptide. This metabolic product is subsequently cleaved by an amastatin-sensitive aminopeptidase to yield the the C-terminal pentapeptide, as treatment with the competitive aminoexopeptidase inhibitor, amastatin, results in a significant accumulation of the C-terminal hexapeptide. Interestingly, Dip-AST 5 (DRLYSFGLa) (6 microM), which in common with Dip-AST 7 and 9 possesses Arg-Leu-Tyr, is not rapidly cleaved. However, [3H-Tyr]Dip-AST 5 at physiological concentrations (4 nM), appears to be cleaved by the same enzymes that cleave Dip-AST 7 and 9, albeit at a reduced rate. Incubation of other members of the Dip-allatostatin family with hemolymph also results in cleavage of the peptides, suggesting that there are a variety of endo- and/or exopeptidases present in the hemolymph of D. punctata.

Hydrolysis of insect neuropeptides by an angiotensin-converting enzyme from the housefly, Musca domestica.

The presence in insect tissues of peptides with structural similarities to angiotensin I and to bradykinin, the two best known substrates of mammalian angiotensin-converting enzyme, has not been reported. As part of our study to identify potential substrates for insect angiotensin-converting enzyme, we have investigated the susceptibility of a number of known insect peptide hormones and neurotransmitters to hydrolysis by Musca domestica angiotensin-converting enzyme. Insect peptides belonging to the red pigment-concentrating hormone, leucokinin, locust tachykinin, and depolarizing peptide families were hydrolyzed by housefly angiotensin-converting enzyme, whereas proctolin and crustacean cardioactive peptide were not substrates. Cus-DP II, LK I, LK II, and Lom-TK I were all cleaved at the penultimate C-terminal peptide bond to release a dipeptide amide as a major fragment with Km values of 94 +/- 11, 634 +/- 8, and 296 +/- 35 microM for Cus-DP II, LK I, and Lom-TK I, respectively. The ability of insect angiotensin-converting enzyme to hydrolyze C-terminally amidated peptides in vitro might be of functional significance because the enzyme has been localized to neuropile regions of the insect brain and is present in the hemolymph of houseflies.

Identification and partial characterization of receptors for allatostatins in brain and corpora allata of the cockroach Diploptera punctata using a binding assay and photoaffinity labeling.

We have developed both an in vitro binding assay and a photoaffinity labeling assay to demonstrate and partially characterize putative receptors for allatostatins in brain and in corpora allata of Diploptera punctata. Isolated brain membranes were photoaffinity labeled with 125I-RYBPA (photoaffinity analogue of dip-allatostatin 5). Following labeling with 125I-RYBPA, SDS-PAGE and autoradiography revealed the presence of a putative receptor (37 kDa) for dip-allatostatin 5 and dip-allatostatin 7. Specific labeling was demonstrated by dose-dependent competition with either dip-allatostatin 5 or dip-allatostatin 7. The in vitro binding assay indicated that the receptor for dip-allatostatin 5 had a Kd of (9.0 +/- 0.9).10(-10) M and Bmax of 2.2 +/- 0.3 pmol/mg membrane protein. For dip-allatostatin 7, two Kd values of (1.5 +/- 0.1).10(-9) M and (3.8 +/- 0.3).10(-9) M were obtained, with Bmax values of 7.2 +/- 0.7 pmol/mg membrane protein and 11.4 +/- 1.0 pmol/mg membrane protein respectively. This indicates that there were probably two putative receptor sites for dip-allatostatin 7 although only one band was observable following photoaffinity labeling. Binding was saturable, specific and reversible. Using the in vitro binding assay, the Kd of the putative receptor in CA for dip-allatostatin 7 was shown to be (7.2 +/- 0.9).10(-10) M.

Cross reactivity studies of CRF-related peptides on insect Malpighian tubules.

Manduca sexta diuretic peptide II (Mas-DPII) stimulates fluid secretion by adult Malpighian tubules and cyclic AMP production by larval proximal and adult tubules of M. sexta in a dose-dependent manner. Mas-DPII has no effect on fluid transport across the larval cryptonephric complex. M. sexta diuretic hormone (Mas-DH) and CRF-related insect diuretic peptides from Acheta domesticus, Locusta migratoria, and Periplaneta americana also cause similar increases in the production of cyclic AMP by the Malpighian tubules of both larval and adult M. sexta. Insect CRF-related diuretic peptides exhibit varying degrees of potency when assayed on Malpighian tubules from L. migratoria and A. domesticus. Sauvagine, bovine-CRF, and human-CRF have only a small, but significant, effect on cyclic AMP production by M. sexta Malpighian tubules. However, sauvagine, bovine-CRF, and sucker fish urotensin-I have no effect on L. migratoria tubules. Stimulation of cyclic AMP production by M. sexta Malpighian tubules could potentially be used as a screening assay to identify other insect CRF-related diuretic peptides.

Structure-activity relationships for Periplaneta americana hypertrehalosemic hormone. I: The importance of side chains and termini.

Single amino acid replacement analogues for the native hypertrehalosemic hormone I of the American cockroach, Periplaneta americana (Pea-CAH-I: pGlu-Val-Asn-Phe-Ser-Pro-Asn-Trp-NH2), have been prepared by solid-phase peptide synthesis, and complete dose-response curves have been measured in P. americana monitoring the carbohydrate-mobilizing activity in vivo. All analogues that elicited hypertrehalosemia showed similar time-response courses, indicating that transport and degradation rates were comparable. Comparison of the potency and efficacy parameters of the analogues under study in the dose-response curves revealed four activity groups: 1) analogues that had the aromatic amino acids at positions 4 (phenylalanine) or 8 (tryptophan) replaced by alanine and glycine, respectively, had trace activity; 2) analogues with alanine at positions 1 or 2 had low potencies and an apparent biphasic dose-response relationship without much observable loss of efficacy; 3) analogues with glycine at positions 6 and 7 had potencies and efficacies most similar to Pea-CAH-I; and 4) analogues that had either an alanine instead of asparagine residue at position 3, or had a substitution of the carboxylamide function at the C-terminus by a carboxyl function reached apparent saturation, but only achieved 50-57% of the maximum activity of the native peptide. The potency profile for the analogue set is consistent with the importance of the N-terminal pentapeptide and the C-terminal tryptophan interacting with receptor(s) more closely than the side chains at positions 6 and 7, which are predicted to be the corner residues of a beta-turn. Finally, the biphasic dose-response curves observed for more than one analogue suggest the potential that receptors for Pea-CAH-I exist in more than one form.

Culekinin depolarizing peptide: a mosquito leucokinin-like peptide that influences insect Malpighian tubule ion transport.

A peptide termed culekinin depolarizing peptide (CDP) was isolated from approximately 1.2 million mosquitos (94% Culex salinarius). The peptide was isolated on the basis of a rapid myotropic assay that utilized a hindgut preparation from Leucophaea maderae and a transepithelial voltage assay that used mosquito Malpighian tubules from Aedes aegypti. A 15% trifluoroacetic acid extraction from the mosquitos, two solid phase extraction steps, and six HPLC steps resulted in the isolation of 9.7 nmol of CDP. This value corresponds to approximately 8 fmol/mosquito. Edman degradation indicated the following sequence for CDP: Asn-Pro-Phe-His-Ser-Trp-Gly-NH2. The sequence was confirmed as the suspected C-terminal amide form of the peptide, since native and synthetic CDP had identical chemical and biological properties. CDP is a member of the leucokinin family of neuropeptides. The leucokinins have been found in three other insect species (Leucophaea maderae, Acheta domesticus and Locusta migratoria) where these peptides were isolated by their myotropic properties alone. CDP shares a C-terminal sequence homology (i.e., Phe-X-Ser-Trp-Gly-NH2) with the rest of the leucokinins. CDP corresponds to the strongest tubule depolarizing activity in the C. salinarius extract. These findings agree with previous structure-activity studies that suggest that mosquitos would contain a leucokinin-like factor that had Phe-His-Ser-Trp-Gly-NH2 as the C-terminal pentapeptide. This is the first leucokinin isolated from blood feeding or holometabolous insects.

Partial identification, synthesis and immunolocalization of locustamyoinhibin, the third myoinhibiting neuropeptide isolated from Locusta migratoria.

A blocked neuropeptide that suppresses the motility of the cockroach hindgut has been isolated from an extract of 9000 brain-corpora cardiaca-corpora allata-suboesophageal ganglion complexes of Locusta migratoria. Biological activity was monitored during HPLC purification by observing the myoinhibiting activity of column fractions on the isolated hindgut of Leucophaea maderae. Due to the low amount of material left after deblocking, this myoinhibiting peptide--designated as locustamyoinhibin or Lom-MIH--could only be partially sequenced: pGlu-X-Tyr-X'-Lys-Gln-Ser-Ala-Phe-Asn-Ala-Val-Ser-NH2. Nevertheless, the carboxy-terminal nonamer sequence (Lom-MIH5-13) was synthesized and also displayed myoinhibiting activity, indicating that the biologically active core lies in the carboxy-terminal sequence. Lom-MIH shows no sequence similarities with other peptides from vertebrate or invertebrate sources and is the third myoinhibiting peptide identified in Locusta migratoria. A polyclonal antiserum was raised against Lom-MIH5-13 and used to investigate the distribution of immunoreactive peptide in the central nervous system and its associated neurohaemal structures. Two groups of neurons with somata in the optic lobes show locustamyoinhibin (Lom-MIH)-like immunoreactivity. These groups have somata at the dorsal and ventral edge of the lamina ganglionaris. The neurons have dense ramifications in the lamina, with processes extending into the first optic chiasma and into the accessory medulla. Four cell bodies were detected in the protocerebrum, and two cells were found at the externo-lateral edge of the tritocerebrum. No immunoreactive perikarya could be observed in the suboesophageal ganglion nor in the ganglia of the ventral nerve cord. Neither the corpora cardiaca nor the neurohaemal organs of the ventral nerve cord showed immunolabelling. Therefore, our findings provide anatomical evidence for a central neurotransmitter role of Lom-MIH.

The detection of AKH/HrTH-like peptides in Ascaridia galli and Ascaris suum using an insect hyperglycaemic bioassay.

Evidence for the presence of adipokinetic hormone/hypertrehalosaemic hormone (AKH/HrTH)-like peptides in the parasitic nematodes Ascaridia galli and Ascaris suum has been obtained using insect bioassays which measure hyperglycaemic responses to peptides belonging to the AKH/HrTH family of insect hormones. A peptide fraction extracted from heads and tails of Ascaridia galli evoked a dose-dependent hyperglycaemic response when injected into the cockroach, Periplaneta americana. Maximal bioactivity was obtained with material that was equivalent to 38 mg (wet weight) of nematode. Bioactivity appeared to be highest in extracts from heads and tails of both male and female worms and could be fractionated into at least three peaks of hyperglycaemic activity by reversed-phase high-performance liquid chromatography. An extract from heads and tails of A. suum also evoked a hyperglycaemic response when injected into the cockroach, Blaberus discoidalis. The bioactivity was inactivated on incubation with pure endopeptidase 24.11, confirming the peptidic nature of the bioactive material. These results provide evidence for the existence of peptides related to the insect AKH/HrTH family of peptides in parasitic nematodes.

Characterization and localization of mosquito-gut receptors for trypsin modulating oostatic factor using a complementary peptide and immunocytochemistry.

The gut receptor of trypsin-modulating oostatic factor (TMOF), a decapeptide hormone that regulates trypsin biosynthesis in the mosquito gut, has been characterized. The binding of TMOF to mosquito gut membranes reached maximum at pH 7.4 and 24 degrees C. No binding was observed at pH 2.5 and the binding to the membranes declined rapidly at pH 8.0. At equilibrium, maximum binding to the receptor was observed at 60 min and 24 degrees C. A synthetic complementary decapeptide NH2-Ile-Leu-Gly-Arg-Gly-Gly-Gly-Gly-Gly-Gly-COOH (FOMT) for TMOF successfully competed with the gut receptor, and specifically bound TMOF (Kd = 4 microM and Kassoc = 2.5 x 10(5) M-1). TMOF binding to gut membranes was characterized with FOMT and a specific ELISA to the hormone at 24 and 72 h after blood feeding. Two classes of binding sites were found on the gut membrane; high affinity (Kd1 = 4.6 +/- 0.7 x 10(-7) M; Kassoc = 2.2 x 10(6) M-1 Bmax = 0.1 pmol/gut) and low affinity (Kd2 = 4.43 +/- 1 x 10(-6) M; Kassoc = 2.3 x 10(5) M-1; Bmax = 0.2 pmol/gut). The total binding sites for high and low affinity classes of TMOF per gut were estimated as 6.3 x 10(10) and 1.1 x 10(11) sites, respectively. Specific binding sites on the gut increased after the blood meal and were visualized by immunocytochemical staining. These results suggest that TMOF regulates trypsin biosynthesis by binding to specific receptor sites that are located on the mosquito gut, and that this receptor can be studied using a complementary peptide approach.