Substrate Cooperativity in Marine Luciferases

Marine luciferases are increasingly used as reporters to study gene regulation. These luciferases have utility in bioluminescent assay development, although little has been reported on their catalytic properties in response to substrate concentration. Here, we report that the two marine luciferases from the copepods, Gaussia princeps (GLuc) and Metridia longa (MLuc) were found, surprisingly, to produce light in a cooperative manner with respect to their luciferin substrate concentration; as the substrate concentration was decreased 10 fold the rate of light production decreased 1000 fold. This positive cooperative effect is likely a result of allostery between the two proposed catalytic domains found in Gaussia and Metridia. In contrast, the marine luciferases from Renilla reniformis (RLuc) and Cypridina noctiluca (CLuc) demonstrate a linear relationship between the concentration of their respective luciferin and the rate of light produced. The consequences of these enzyme responses are discussed

Thymic-derived tolerizing dendritic cells are upregulated in the spleen upon treatment with intravenous immunoglobulin in a murine model of immune thrombocytopenia

Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder characterized by low platelet counts. First-line treatment includes intravenous immunoglobulin (IVIg), however, its working mechanism remains incompletely understood. We investigated splenic and thymic dendritic cell (DC) subsets upon IVIg treatment in a well-characterized active murine model of ITP. During active disease, there was a significant peripheral deficiency of splenic tolerizing SIRPα+ DCs which could be rescued by IVIg therapy, increasing platelet counts. These splenic tolerizing DC changes were associated with an abrogation of the thymic-retention of tolerizing DCs, suggesting that IVIg may raise platelet counts in ITP by modulating peripheral numbers of tolerizing DCs