@article {Susa300,
	title = {Cryo-EM structure of the B cell co-receptor CD19 bound to the tetraspanin CD81},
	journal = {Science},
	volume = {371},
	number = {6526},
	year = {2021},
	pages = {300{\textendash}305},
	publisher = {American Association for the Advancement of Science},
	abstract = {A core component of the immune system are B cells, which are activated by infection and then mature to provide long-lived immunity. Activation is initiated when a cell surface B cell receptor, in association with its coreceptor, recognizes an antigen. Susa et al. report a structure of the B cell receptor CD81 in complex with its co receptor, CD19. CD81 alone binds to cholesterol, but the conformational changes associated with binding to CD19 occlude the cholesterol-binding pocket. Regulating cholesterol binding could play a role in the activation mechanism. The structure also provides a basis for the design of immunotherapies.Science, this issue p. 300Signaling through the CD19-CD81 co-receptor complex, in combination with the B cell receptor, is a critical determinant of B cell development and activation. It is unknown how CD81 engages CD19 to enable co-receptor function. Here, we report a 3.8-angstrom structure of the CD19-CD81 complex bound to a therapeutic antigen-binding fragment, determined by cryo{\textendash}electron microscopy (cryo-EM). The structure includes both the extracellular domains and the transmembrane helices of the complex, revealing a contact interface between the ectodomains that drives complex formation. Upon binding to CD19, CD81 opens its ectodomain to expose a hydrophobic CD19-binding surface and reorganizes its transmembrane helices to occlude a cholesterol binding pocket present in the apoprotein. Our data reveal the structural basis for CD19-CD81 complex assembly, providing a foundation for rational design of therapies for B cell dysfunction.},
	issn = {0036-8075},
	doi = {10.1126/science.abd9836},
	url = {https://science.sciencemag.org/content/371/6526/300},
	author = {Susa, Katherine J. and Rawson, Shaun and Kruse, Andrew C. and Blacklow, Stephen C.}
}
