MrgX2 is a promiscuous receptor for basic peptides causing mast cell pseudo-allergic and anaphylactoid reactions.

Activation of MrgX2, an orphan G protein-coupled receptor expressed on mast cells, leads to degranulation and histamine release. Human MrgX2 binds promiscuously to structurally diverse peptides and small molecules that tend to have basic properties (basic secretagogues), resulting in acute histamine-like adverse drug reactions of injected therapeutic agents. We set out to identify MrgX2 orthologues from other mammalian species used in nonclinical stages of drug development. Previously, the only known orthologue of human MrgX2 was from mouse, encoded by Mrgprb2. MrgX2 genes of rat, dog (beagle), minipig, pig, and Rhesus and cynomolgus monkey were identified by bioinformatic approaches and verified by their ability to mediate calcium mobilization in transfected cells in response to the classical MrgX2 agonist, compound 48/80. The peptide GSK3212448 is an inhibitor of the PRC2 epigenetic regulator that caused profound anaphylactoid reactions upon intravenous infusion to rat. We showed GSK3212448 to be a potent MrgX2 agonist particularly at rat MrgX2. We screened sets of drug-like molecules and peptides to confirm the highly promiscuous nature of MrgX2. Approximately 20% of drug-like molecules activated MrgX2 (pEC50 ranging from 4.5 to 6), with the principle determinant being basicity. All peptides tested of net charge +3 or greater exhibited agonist activity, including the cell penetrating peptides polyarginine (acetyl-Arg9-amide) and TAT (49-60), a fragment of HIV-1 TAT protein. Finally, we showed that the glycopeptide antibiotic vancomycin, which is associated with clinical pseudo-allergic reactions known as red man syndrome, is an agonist of MrgX2.

Rapid, Antibody-Free Detection of Recombinant Proteins on Blots Using Enzyme Fragment Complementation.

Alternative, antibody-free techniques to western analysis of protein blots can offer reduced assay times for routine analysis of expression of recombinant proteins. We have adapted the commercially available enzyme fragment complementation technology to provide a rapid protein detection method for protein blots based on significantly reducing the number of incubation and washing steps used in traditional approaches, and eliminating the requirement for antibodies. In this chapter, we highlight the use of this assay for measuring recombinant protein expressed in mammalian cells for a range of applications, including dot blot screening of large numbers of different cell samples, assessment of protein integrity through detection of degradation bands, and characterization of posttranslational protein modifications such as glycosylation.

Rapid, antibody-free detection of recombinant proteins on blots using enzyme fragment complementation.

Alternative, antibody-free techniques to western analysis of protein blots can offer reduced assay times for routine analysis of expression of recombinant proteins. We have adapted the commercially available enzyme fragment complementation technology to provide a rapid protein detection method for protein blots based on significantly reducing the number of incubation and washing steps used in traditional approaches, and eliminating the requirement for antibodies. In this article, we highlight the use of this assay for measuring recombinant protein expressed in mammalian cells for a range of applications, including dot blot screening of large numbers of different cell samples, assessment of protein integrity through detection of degradation bands, and characterization of post-translational protein modifications such as glycosylation.

A generic, homogenous method for measuring kinase and inhibitor activity via adenosine 5'-diphosphate accumulation.

The authors describe an assay to measure the generation of adenosine 5'-diphosphate (ADP) resulting from phosphorylation of a substrate by a kinase. ADP accumulation is detected by conversion to a fluorescent signal via a coupled enzyme system. The technology has potential applications for the assessment of inhibitor potency and mode of action as well as kinetic analysis of enzyme activity. The assay has a wide dynamic range (0.25-75 microM) and has been validated with several kinases including the highly active cyclic adenosine monophosphate-dependent protein kinase (PKAalpha), casein kinase 1 (CK1), and the weakly active kinase Jun N-terminal kinase 2 (Jnk2alpha2). Kinase activity can be measured either in an end point or continuous mode. Assay performance in end point mode was compared with an adenosine 5'-triphosphate (ATP) depletion assay and in continuous mode with a pyruvate kinase/lactate dehydrogenase coupled assay. The ability to characterize kinase kinetics was demonstrated by deriving ATP/substrate affinity (Michaelis-Menten constant; K(m)) values for PKAalpha, CK1, and Jnk2alpha2. The assay readily measured activity with kinase reactions using protein substrates, indicating the suitability for use with large macromolecules. A wide range of inhibitor activities could be determined even in the presence of high ATP concentrations, making the assay highly suitable to characterize the mode of action of the inhibitor in question. Collectively, this assay provides a homogenous, generic method for a number of applications in kinase drug discovery.

Differential effects of unnatural sialic acids on the polysialylation of the neural cell adhesion molecule and neuronal behavior.

In this study we have examined how unnatural sialic acids can alter polysialic acid expression and influence the adhesive properties of the neural cell adhesion molecule (NCAM). Unnatural sialic acids are generated by metabolic conversion of synthetic N-acyl mannosamines and are typically incorporated into cell-surface glycoconjugates. However, N-butanoylmannosamine and N-pentanoylmannosamine are effective inhibitors of polysialic acid (PSA) synthesis in stably transfected HeLa cells expressing NCAM and the polysialyltransferase STX. These cells were used as substrates to examine the effect of inhibiting PSA synthesis on the development of neurons derived from the chick dorsal root ganglion. N-butanoylmannosamine blocked polysialylation of NCAM and significantly reduced neurite outgrowth comparable with enzymatic removal of PSA by endoneuraminidases. As a result, neurite outgrowth was similar to that observed for non-polysialylated NCAM. In contrast, previous studies have shown that N-propanoyl sialic acid (SiaProp), generated from N-propanoylmannosamine, is readily accepted by polysialyltransferases and permits the extension of poly(SiaProp) on NCAM. Despite being immunologically distinct, poly(SiaProp) can promote neurite outgrowth similarly to natural polysialic acid. Thus, subtle structural differences in PSA resulting from the incorporation of SiaProp residues do not alter the antiadhesive properties of polysialylated NCAM.