Oct 28, 2019

Phagocytosis is a process mediated by the body’s immune cells to remove and destroy particles like pathogens and debris. In order to do so, phagocytic cells, such as macrophages and neutrophils, deform their plasma membranes to engulf and consume the target particle(s) by encapsulating them within organelles known as the phagosome.

Until recently, it was a mystery as to how macrophages, which are only 20 microns wide, were capable of deforming their membranes to establish phagocytic cups that can measure microns in length. In a recent study, Hanawa-Suetsugu et al. found that GAS7, a protein expressed in macrophages, played a key role in marking these regions of membrane deformation. A feature of GAS7 is a region on the protein known as the F-BAR domain. Crystal structures of the F-BAR domain revealed that it could form a helical-bundle dimer that possessed an extremely flat, shallow concave curvature. These dimers could then interact with other dimers to form flat filamentous oligomers (FFOs), which when assembled, formed GAS7 striations on the cell membrane. The scientists went on to experimentally elucidate that oligomerization, coupled with the binding of GAS7 to the macrophage’s cell membrane, play critical roles in initiating phagocytosis through the formation of the phagocytic cup.

There is still much to learn about how macrophages extensively remodel their dynamic cell membranes to do their job as professional phagocytes. However, it is both exciting, and perhaps a little humbling, to peek into the clever mechanisms that underlie just how these cells are able to bite off more than we think they can chew.

• Hanawa-Suetsugu K, Itoh Y, Ab Fatah M, et al. Phagocytosis is mediated by two-dimensional assemblies of the F-BAR protein GAS7. Nat. Commun. 10(1), 4763 (2019).

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