Proteolytically Activated CRAC Effectors through Designed Intramolecular Inhibition

On-demand treatment of metabolic diseases by a synthetic drug-inducible exocytosis system

Here, we present StimExo as a rational design strategy allowing various user-defined control signals to trigger calcium-dependent exocytosis and mediate on-demand protein secretion in cell-therapy settings. Using a modular framework incorporating inducible protein-protein interactions into an engineered bipartite activator of calcium release-activated calcium (CRAC) channels, Ca2+ influx mediated by the STIM/Orai1 machinery was flexibly adjusted to depend on different user-defined input signals. Application of StimExo to various endocrine cells enables instant secretion of therapeutic hormones upon administration of safe and patient-compliant trigger compounds. StimExo also mediated insulin exocytosis using a cell-based gene delivery strategy in vivo, accounting for real-time control of blood glucose homeostasis in male diabetic mice in response to the FDA-approved drug grazoprevir. This study achieves true "sense-and-respond" cell-based therapies and provides a platform for remote control of in vivo transgene activities using various trigger signals of interest.

The art of designed coiled-coils for the regulation of mammalian cells

Synthetic biology aims to engineer complex biological systems using modular elements, with coiled-coil (CC) dimer-forming modules are emerging as highly useful building blocks in the regulation of protein assemblies and biological processes. Those small modules facilitate highly specific and orthogonal protein-protein interactions, offering versatility for the regulation of diverse biological functions. Additionally, their design rules enable precise control and tunability over these interactions, which are crucial for specific applications. Recent advancements showcase their potential for use in innovative therapeutic interventions and biomedical applications. In this review, we discuss the potential of CCs, exploring their diverse applications in mammalian cells, such as synthetic biological circuit design, transcriptional and allosteric regulation, cellular assemblies, chimeric antigen receptor (CAR) T cell regulation, and genome editing and their role in advancing the understanding and regulation of cellular processes.

Synthetic Biology Meets Ca2+ Release-Activated Ca2+ Channel-Dependent Immunomodulation

Many essential biological processes are triggered by the proximity of molecules. Meanwhile, diverse approaches in synthetic biology, such as new biological parts or engineered cells, have opened up avenues to precisely control the proximity of molecules and eventually downstream signaling processes. This also applies to a main Ca2+ entry pathway into the cell, the so-called Ca2+ release-activated Ca2+ (CRAC) channel. CRAC channels are among other channels are essential in the immune response and are activated by receptor-ligand binding at the cell membrane. The latter initiates a signaling cascade within the cell, which finally triggers the coupling of the two key molecular components of the CRAC channel, namely the stromal interaction molecule, STIM, in the ER membrane and the plasma membrane Ca2+ ion channel, Orai. Ca2+ entry, established via STIM/Orai coupling, is essential for various immune cell functions, including cytokine release, proliferation, and cytotoxicity. In this review, we summarize the tools of synthetic biology that have been used so far to achieve precise control over the CRAC channel pathway and thus over downstream signaling events related to the immune response.