Fluorogenic Granzyme A Substrates Enable Real-Time Imaging of Adaptive Immune Cell Activity.

Cytotoxic immune cells, including T lymphocytes (CTLs) and natural killer (NK) cells, are essential components of the host response against tumors. CTLs and NK cells secrete granzyme A (GzmA) upon recognition of cancer cells; however, there are very few tools that can detect physiological levels of active GzmA with high spatiotemporal resolution. Herein, we report the rational design of the near-infrared fluorogenic substrates for human GzmA and mouse GzmA. These activity-based probes display very high catalytic efficiency and selectivity over other granzymes, as shown in tissue lysates from wild-type and GzmA knock-out mice. Furthermore, we demonstrate that the probes can image how adaptive immune cells respond to antigen-driven recognition of cancer cells in real time.

Fluorogenic Granzyme A Substrates Enable Real-Time Imaging of Adaptive Immune Cell Activity.

Cytotoxic immune cells, including T lymphocytes (CTLs) and natural killer (NK) cells, are essential components of the host response against tumors. CTLs and NK cells secrete granzyme A (GzmA) upon recognition of cancer cells; however, there are very few tools that can detect physiological levels of active GzmA with high spatiotemporal resolution. Herein, we report the rational design of the near-infrared fluorogenic substrates for human GzmA and mouse GzmA. These activity-based probes display very high catalytic efficiency and selectivity over other granzymes, as shown in tissue lysates from wild-type and GzmA knock-out mice. Furthermore, we demonstrate that the probes can image how adaptive immune cells respond to antigen-driven recognition of cancer cells in real time.

The Structural and Biochemical Characterization of UNC119B Cargo Binding and Release Mechanisms.

Two paralogs of the guanine dissociation inhibitor-like solubilizing factors UNC119, UNC119A and UNC119B, are present in the human genome. UNC119 binds to N-myristoylated proteins and masks the hydrophobic lipid from the hydrophilic cytosol, facilitating trafficking between different membranes. Two classes of UNC119 cargo proteins have been classified: low affinity cargoes, released by the Arf-like proteins ARL2 and ARL3, and high affinity cargoes, which are specifically released by ARL3 and trafficked to either the primary cilium or the immunological synapse. The UNC119 homologues have reported differences in functionality, but the structural and biochemical bases for these differences are unknown. Using myristoylated peptide binding and release assays, we show that peptides sharing the previously identified UNC119A high affinity motif show significant variations of binding affinities to UNC119B of up to 427-fold. Furthermore, we solve the first two crystal structures of UNC119B, one in complex with the high affinity cargo peptide of LCK and a second one in complex with the release factor ARL3. Using these novel structures, we identify a stretch of negatively charged amino acids unique to UNC119B that may undergo a conformational change following binding of a release factor which we propose as an additional release mechanism specific to UNC119B.

ARL3, a small GTPase with a functionally conserved role in primary cilia and immune synapses.

The primary cilium and the immunological synapse are both specialized functional plasma membrane domains that share several similarities. Signalling output of membrane domains is regulated, spatially and temporally, by segregating and focusing lipids and proteins. ARL3, a small GTPase, plays a major role in concentrating lipid-modified proteins in both the immunological synapse and the primary cilia. Here in this review we will introduce the role of ARL3 in health and disease and its role in polarizing signalling at the primary cilia and immunological synapses.