A streamlined, automated workflow to screen and triage large numbers of baculoviruses for protein expression

The baculovirus expression system is a powerful and widely used method to generate large quantities of recombinant protein. However, challenges exist in workflows utilizing either liquid baculovirus stocks or the Titerless Infected-Cells Preservation and Scale-Up (TIPS) method, including the time and effort to generate baculoviruses, screen for protein expression and store large numbers of baculovirus stocks. To mitigate these challenges, we have developed a streamlined, hybrid workflow which utilizes high titer liquid virus stocks for rapid plate-based protein expression screening, followed by a TIPS-based scale-up for larger protein production efforts. Additionally, we have automated each step in this screening workflow using a custom robotic system. With these process improvements, we have significantly reduced the time, effort and resources required to manage large baculovirus generation and expression screening campaigns.

Structural characterization of M8C10, a neutralizing antibody targeting a highly conserved prefusion-specific epitope on the metapneumovirus fusion trimerization interface

IMPORTANCE

Human metapneumovirus (hMPV) is a common pathogen causing lower respiratory tract infections worldwide and can develop severe symptoms in high-risk populations such as infants, the elderly, and immunocompromised patients. There are no approved hMPV vaccines or neutralizing antibodies available for therapeutic or prophylactic use. The trimeric hMPV fusion F protein is the major target of neutralizing antibodies in human sera. Understanding the immune recognition of antibodies to hMPV-F antigen will provide critical insights into developing efficacious hMPV monoclonal antibodies and vaccines.

Structural basis for selectivity and diversity in angiotensin II receptors

Angiotensin II receptors, AT₁R and AT₂R, serve as key components of the renin-angiotensin-aldosterone system. While AT₁R plays a central role in the regulation of blood pressure, the function of AT₂R is enigmatic with a variety of reported effects. To elucidate the mechanisms for the functional diversity and ligand selectivity between these receptors, we report crystal structures of the human AT₂R bound to an AT₂R-selective and an AT₁R/AT₂R-dual ligand, respectively, capturing the receptor in an active-like conformation. Unexpectedly, helix VIII was found in a non-canonical position, stabilizing the active-like state, but at the same time preventing the recruitment of G proteins/β-arrestins, in agreement with the lack of signaling responses in standard cellular assays. Structure-activity relationship, docking and mutagenesis studies revealed the interactions critical for ligand binding and selectivity. Our results thus provide insights into the structural basis for distinct functions of the angiotensin receptors, and may guide the design of novel selective ligands.

Insights into activity and inhibition from the crystal structure of human O-GlcNAcase

O-GlcNAc hydrolase (OGA) catalyzes removal of βα-linked N-acetyl-D-glucosamine from serine and threonine residues. We report crystal structures of Homo sapiens OGA catalytic domain in apo and inhibited states, revealing a flexible dimer that displays three unique conformations and is characterized by subdomain α-helix swapping. These results identify new structural features of the substrate-binding groove adjacent to the catalytic site and open new opportunities for structural, mechanistic and drug discovery activities.

Integration of Affinity Selection-Mass Spectrometry and Functional Cell-Based Assays to Rapidly Triage Druggable Target Space within the NF-κB Pathway

The primary objective of early drug discovery is to associate druggable target space with a desired phenotype. The inability to efficiently associate these often leads to failure early in the drug discovery process. In this proof-of-concept study, the most tractable starting points for drug discovery within the NF-κB pathway model system were identified by integrating affinity selection-mass spectrometry (AS-MS) with functional cellular assays. The AS-MS platform Automated Ligand Identification System (ALIS) was used to rapidly screen 15 NF-κB proteins in parallel against large-compound libraries. ALIS identified 382 target-selective compounds binding to 14 of the 15 proteins. Without any chemical optimization, 22 of the 382 target-selective compounds exhibited a cellular phenotype consistent with the respective target associated in ALIS. Further studies on structurally related compounds distinguished two chemical series that exhibited a preliminary structure-activity relationship and confirmed target-driven cellular activity to NF-κB1/p105 and TRAF5, respectively. These two series represent new drug discovery opportunities for chemical optimization. The results described herein demonstrate the power of combining ALIS with cell functional assays in a high-throughput, target-based approach to determine the most tractable drug discovery opportunities within a pathway.

Structure and Function of the Hypertension Variant A486V of G Protein-coupled Receptor Kinase 4

G-protein-coupled receptor (GPCR) kinases (GRKs) bind to and phosphorylate GPCRs, initiating the process of GPCR desensitization and internalization. GRK4 is implicated in the regulation of blood pressure, and three GRK4 polymorphisms (R65L, A142V, and A486V) are associated with hypertension. Here, we describe the 2.6 Å structure of human GRK4α A486V crystallized in the presence of 5'-adenylyl β,γ-imidodiphosphate. The structure of GRK4α is similar to other GRKs, although slight differences exist within the RGS homology (RH) bundle subdomain, substrate-binding site, and kinase C-tail. The RH bundle subdomain and kinase C-terminal lobe form a strikingly acidic surface, whereas the kinase N-terminal lobe and RH terminal subdomain surfaces are much more basic. In this respect, GRK4α is more similar to GRK2 than GRK6. A fully ordered kinase C-tail reveals interactions linking the C-tail with important determinants of kinase activity, including the αB helix, αD helix, and the P-loop. Autophosphorylation of wild-type GRK4α is required for full kinase activity, as indicated by a lag in phosphorylation of a peptide from the dopamine D1 receptor without ATP preincubation. In contrast, this lag is not observed in GRK4α A486V. Phosphopeptide mapping by mass spectrometry indicates an increased rate of autophosphorylation of a number of residues in GRK4α A486V relative to wild-type GRK4α, including Ser-485 in the kinase C-tail.

Structural basis for selective small molecule kinase inhibition of activated c-Met

The receptor tyrosine kinase c-Met is implicated in oncogenesis and is the target for several small molecule and biologic agents in clinical trials for the treatment of cancer. Binding of the hepatocyte growth factor to the cell surface receptor of c-Met induces activation via autophosphorylation of the kinase domain. Here we describe the structural basis of c-Met activation upon autophosphorylation and the selective small molecule inhibiton of autophosphorylated c-Met. MK-2461 is a potent c-Met inhibitor that is selective for the phosphorylated state of the enzyme. Compound 1 is an MK-2461 analog with a 20-fold enthalpy-driven preference for the autophosphorylated over unphosphorylated c-Met kinase domain. The crystal structure of the unbound kinase domain phosphorylated at Tyr-1234 and Tyr-1235 shows that activation loop phosphorylation leads to the ejection and disorder of the activation loop and rearrangement of helix αC and the G loop to generate a viable active site. Helix αC adopts a orientation different from that seen in activation loop mutants. The crystal structure of the complex formed by the autophosphorylated c-Met kinase domain and compound 1 reveals a significant induced fit conformational change of the G loop and ordering of the activation loop, explaining the selectivity of compound 1 for the autophosphorylated state. The results highlight the role of structural plasticity within the kinase domain in imparting the specificity of ligand binding and provide the framework for structure-guided design of activated c-Met inhibitors.

Structural definition and substrate specificity of the S28 protease family: the crystal structure of human prolylcarboxypeptidase

BACKGROUND

The unique S28 family of proteases is comprised of the carboxypeptidase PRCP and the aminopeptidase DPP7. The structural basis of the different substrate specificities of the two enzymes is not understood nor has the structure of the S28 fold been described.

RESULTS

The experimentally phased 2.8 A crystal structure is presented for human PRCP. PRCP contains an alpha/beta hydrolase domain harboring the catalytic Asp-His-Ser triad and a novel helical structural domain that caps the active site. Structural comparisons with prolylendopeptidase and DPP4 identify the S1 proline binding site of PRCP. A structure-based alignment with the previously undescribed structure of DPP7 illuminates the mechanism of orthogonal substrate specificity of PRCP and DPP7. PRCP has an extended active-site cleft that can accommodate proline substrates with multiple N-terminal residues. In contrast, the substrate binding groove of DPP7 is occluded by a short amino-acid insertion unique to DPP7 that creates a truncated active site selective for dipeptidyl proteolysis of N-terminal substrates.

CONCLUSION

The results define the structure of the S28 family of proteases, provide the structural basis of PRCP and DPP7 substrate specificity and enable the rational design of selective PRCP modulators.

Expression, purification and crystallization of human prolylcarboxypeptidase

Prolylcarboxypeptidase (PrCP) is a lysosomal serine carboxypeptidase that cleaves a variety of C-terminal amino acids adjacent to proline and has been implicated in diseases such as hypertension and obesity. Here, the robust production, purification and crystallization of glycosylated human PrCP from stably transformed CHO cells is described. Purified PrCP yielded crystals belonging to space group R32, with unit-cell parameters a = b = 181.14, c = 240.13 A, that diffracted to better than 2.8 A resolution.

Structural basis of human p70 ribosomal S6 kinase-1 regulation by activation loop phosphorylation

p70 ribosomal S6 kinase (p70S6K) is a downstream effector of the mTOR signaling pathway involved in cell proliferation, cell growth, cell-cycle progression, and glucose homeostasis. Multiple phosphorylation events within the catalytic, autoinhibitory, and hydrophobic motif domains contribute to the regulation of p70S6K. We report the crystal structures of the kinase domain of p70S6K1 bound to staurosporine in both the unphosphorylated state and in the 3'-phosphoinositide-dependent kinase-1-phosphorylated state in which Thr-252 of the activation loop is phosphorylated. Unphosphorylated p70S6K1 exists in two crystal forms, one in which the p70S6K1 kinase domain exists as a monomer and the other as a domain-swapped dimer. The crystal structure of the partially activated kinase domain that is phosphorylated within the activation loop reveals conformational ordering of the activation loop that is consistent with a role in activation. The structures offer insights into the structural basis of the 3'-phosphoinositide-dependent kinase-1-induced activation of p70S6K and provide a platform for the rational structure-guided design of specific p70S6K inhibitors.

Structure of human prostasin, a target for the regulation of hypertension

Prostasin (also called channel activating protease-1 (CAP1)) is an extracellular serine protease implicated in the modulation of fluid and electrolyte regulation via proteolysis of the epithelial sodium channel. Several disease states, particularly hypertension, can be affected by modulation of epithelial sodium channel activity. Thus, understanding the biochemical function of prostasin and developing specific agents to inhibit its activity could have a significant impact on a widespread disease. We report the expression of the prostasin proenzyme in Escherichia coli as insoluble inclusion bodies, refolding and activating via proteolytic removal of the N-terminal propeptide. The refolded and activated enzyme was shown to be pure and monomeric, with kinetic characteristics very similar to prostasin expressed from eukaryotic systems. Active prostasin was crystallized, and the structure was determined to 1.45 A resolution. These apoprotein crystals were soaked with nafamostat, allowing the structure of the inhibited acyl-enzyme intermediate structure to be determined to 2.0 A resolution. Comparison of the inhibited and apoprotein forms of prostasin suggest a mechanism of regulation through stabilization of a loop which interferes with substrate recognition.

Potent 2-[(pyrimidin-4-yl)amine}-1,3-thiazole-5-carbonitrile-based inhibitors of VEGFR-2 (KDR) kinase

Pyrimidino-thiazolyl carbonitriles were prepared that are potent VEGFR-2 (KDR) kinase inhibitors. The modification of lead structures resulted in 3m which exhibited the best overall profile in KDR inhibitory activity, iv/po pharmacokinetics, and reduced hERG affinity.

Potent N-(1,3-Thiazol-2-yl)pyridin-2-amine Vascular Endothelial Growth Factor Receptor Tyrosine Kinase Inhibitors with Excellent Pharmacokinetics and Low Affinity for the hERG Ion Channel

A series of N-(1,3-thiazol-2-yl)pyridin-2-amine KDR kinase inhibitors have been developed that possess optimal properties. Compounds have been discovered that exhibit excellent in vivo potency. The particular challenges of overcoming hERG binding activity and QTc increases in vivo in addition to achieving good pharmacokinetics have been acomplished by discovering a unique class of amine substituents. These compounds have a favorable kinase selectivity profile that can be accentuated with appropriate substitution.

Mouse embryonic stem cells carrying one or two defective Msh2 alleles respond abnormally to oxidative stress inflicted by low-level radiation

Chronic oxidative stress may play a critical role in the pathogenesis of many human cancers. Here, we report that mouse embryonic stem (ES) cells deficient in DNA mismatch repair responded abnormally when exposed to low levels of ionizing radiation, a stress known to generate oxidative DNA damage. ES cells derived from mice carrying either one or two disrupted Msh2 alleles displayed an increased survival following protracted exposures to low-level ionizing radiation as compared with wild-type ES cells. The increases in survival exhibited by ES cells deficient in DNA mismatch repair appeared to have resulted from a failure to efficiently execute cell death (apoptosis) in response to radiation exposure. For each of the ES cell types, prolonged low-level radiation treatment generated oxidative genome damage that manifested as an accumulation of oxidized bases in genomic DNA. However, ES cells from Msh2(+/-) and Msh2(-/-) mice accumulated more oxidized bases as a consequence of low-level radiation exposure than ES cells from Msh2(+/+) mice. The propensity for normal cells with mismatch repair enzyme deficiencies, including cells heterozygous for inactivating mismatch repair enzyme gene mutations, to survive promutagenic genome insults accompanying oxidative stresses may contribute to the increased cancer risk characteristic of the hereditary nonpolyposis colorectal cancer syndrome.

The corticomotor representation of upper limb muscles in writer's cramp and changes following botulinum toxin injection

Transcranial magnetic stimulation was used to investigate the properties of the corticomotor pathway and to map the primary motor cortex projection to hand and forearm muscles during a sustained isometric contraction in a group of subjects with writer's cramp of varying duration. Corticomotor threshold, motor evoked potential amplitude and latency, and silent-period duration were normal on both sides in all subjects. The maps of the corticomotor projection were displaced relative to normal in all subjects, and in some cases were distorted in shape, with extensions of the lateral borders and the emergence of almost discrete secondary motor areas. The degree of map distortion and displacement was greatest in subjects with long-standing writer's cramp (> 5 years), and was bilateral in some cases. Injection of botulinum toxin into affected muscles demonstrated that the alterations in map topography were not fixed, and could be temporarily reversed during the period when the clinical effects of the injection were greatest, with the maps returning to their original positions as the effects of the injection wore off. It is concluded from this study that there are slowly evolving reorganizational changes in the primary motor cortex in writer's cramp, and that these changes may be secondary to altered afferent inputs from both clinically affected and unaffected muscles.

Sensitivity of human prostatic carcinoma cell lines to low dose rate radiation exposure

PURPOSE

Low dose rate radioemitters, such as 125I, 103Pd, and 89Sr, have been used both for local and systemic treatment of prostate cancer. Most normal cells exposed to ionizing radiation characteristically activate cell cycle checkpoints, resulting in cell cycle arrest at the G1/S and G2/M transition points. Cancer cells are typically quite sensitive to radiation killing late in the G2 phase of the replicative cell cycle. Furthermore, most cancer cells accumulating at the G2/M transition point as a result of low dose rate radiation exposure appear to become sensitive to further low dose rate irradiation. For this reason, protracted exposure of cancer cells to low dose rate radiation has been proposed to result in increased cancer cell killing as compared with brief exposures of cancer cells to high dose rate radiation. Since many human prostatic carcinomas contain somatic genome alterations targeting genes which affect the cell cycle and radiation-associated cell cycle checkpoints, we evaluated the effects of low dose rate radiation exposure on the cell cycle and on clonogenic survival for various human prostatic carcinoma cell lines.

MATERIALS AND METHODS

Human prostatic carcinoma cells from the LNCaP, DU 145, PC-3, PPC-1, and TSU-Pr1 cell lines were exposed to low dose rate (0.25 Gy/hour) or high dose rate (60 Gy/hour) radiation in vitro and then assessed for radiation cytotoxicity by clonogenic survival assay. Cell cycle perturbations following protracted exposure to low dose rate radiation were evaluated using flow cytometry.

RESULTS

For LNCaP cells, low dose rate radiation exposure resulted in an accumulation of cells at both the G1/S and the G2/M cell cycle transition points. For DU 145, PC-3, PPC-1, and TSU-Pr1 cells, treatment with low dose rate radiation triggered G2/M cell cycle arrest, but not G1/S arrest. Unexpectedly, the cell cycle redistribution pattern phenotypes observed, G1/S and G2/M cell cycle arrest versus G2/M arrest alone, appeared to have little effect on low dose rate radiation survival. Furthermore, while PC-3, PPC-1, and TSU-Pr1 cells exhibited increased cytotoxic sensitivity to low dose rate versus fractionated high dose rate radiation treatment, DU 145 and LNCaP cells did not.

CONCLUSIONS

Radiation-associated pertubations in replicative cell cycle progression were not dominant determinants of low dose rate radiation killing efficacy in human prostate cancer cell lines in vitro.

Idiopathic focal dystonia: a disorder of muscle spindle afferent processing?

As muscle spindles are involved in the sensation of position and movement of the body, we tested their involvement in the pathophysiology of idiopathic focal dystonia. Twenty patients with torticollis, nine with writer's cramp, two with blepharospasm and 16 healthy control subjects participated. In the first task, the blindfolded subject matched the position of the passively moved forearm with the opposite forearm when the elbow joint was slowly flexed. In a second matching task, passive movement was replaced by stimulation of one biceps tendon with a 50-Hz vibratory stimulus (a selective stimulus for muscle spindle Ia afferents). In normal individuals, this stimulus produces flexion of the vibrated arm around the elbow joint. Movement in both arms was recorded electronically. In experiments without vibratory stimuli, dystonic subjects showed normal movement of the tracking arm during attempts to match the position of the passively moved arm and no difference between the arms in the initial and final steady state positions. In experiments using vibratory stimuli, vibration of biceps tendons in normal subjects elicited flexion of the stimulated arm at the elbow and a matching movement of the opposite arm. In patients with dystonia, there was a similar flexion response to the vibratory stimulus in the stimulated arm but movement of the tracking arm was reduced. Taken together, these experiments suggest that there is abnormal perception of motion, but not position, in dystonic subjects. Dystonic subjects showed bilateral abnormalities of perception of the tonic vibration reflex which were remote from the clinically affected site. These findings are discussed in relationship to the role of muscle spindle Ia afferents in focal dystonia.