Phase separation of signaling molecules promotes T cell receptor signal transduction

Abstract

Activation of various cell surface receptors triggers the reorganization of downstream signaling molecules into micron- or submicron-sized clusters. However, the functional consequences of such clustering has been unclear. We biochemically reconstituted a 12-component signaling pathway on model membranes, beginning with T cell receptor (TCR) activation and ending with actin assembly. When TCR phoshophorylation was triggered, downstream signaling proteins spontaneously separated into liquid-like clusters that promoted signaling outputs both in vitro and in human Jurkat T cells. Reconstituted clusters were enriched in kinases but excluded phosphatases, and enhanced actin filament assembly by recruiting and organizing actin regulators. These results demonstrate that protein phase separation can create a distinct physical and biochemical compartment that facilitates signaling.

Cytoskeletal control of B cell responses to antigens

“…Signalling complexes that activate the ARP2/3 complex can also embed themselves in actin filaments to protect them from dissociation. In this case, actin provides a positive feedback on antigen-induced signalling, particularly when these complexes assemble by otherwise weak interactions 101,102 .…”

To Mix, or To Demix, That Is the Question

“…Given N distinct protein and RNA components, the phase rule states that, for fixed temperature and pressure, there can be at most N þ 2 coexisting phases. And yet, cells are not characterized by~10 4 types of droplets of homogeneous compositions. This implies that there might be certain generic organizing principles that determine the number of coexisting phases within cells.…”

“…Unlike typical intracellular organelles such as mitochondria and nuclei, membraneless organelles lack a surrounding phospholipid membrane. A variety of nuclear (1-3) and cytoplasmic functions (1,2,(4)(5)(6) are associated with membraneless organelles and these include ribosomal biogenesis, RNA processing, and stress response. How do membraneless organelles form, and how are the hundreds of distinct protein and RNA molecules organized within these organelles?…”

“…A typical eukaryotic cell comprises of~10 4 proteins and RNA molecules. Distinct membraneless organelles simultaneously coexist and each organelle comprises of~10 2 types of macromolecules.…”

Development of nanoscale structure in LAT-based signaling complexes

“…These two essential adapter proteins are both needed for proper signal transduction, T cell activation and subsequent immune responses (Yablonski et al, 1998;Zhang et al, 1999b). Recent work has shown that signal transduction from TCR phosphorylation through LAT and SLP-76 clustering to activation of actin polymerization can be reconstructed in vitro (Su et al, 2016).…”