Site-specific functionality and tryptophan mimicry of lipidation in tetraspanin CD9
SourceFEBS Journal, 287, 24, (2020), pp. 5323-5344
Article / Letter to editor
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SubjectRadboudumc 2: Cancer development and immune defence RIMLS: Radboud Institute for Molecular Life Sciences; Radboudumc 4: lnfectious Diseases and Global Health RIMLS: Radboud Institute for Molecular Life Sciences
Lipidation of transmembrane proteins regulates many cellular activities, including signal transduction, cell-cell communication, and membrane trafficking. However, how lipidation at different sites in a membrane protein affects structure and function remains elusive. Here, using native mass spectrometry we determined that wild-type human tetraspanins CD9 and CD81 exhibit nonstochastic distributions of bound acyl chains. We revealed CD9 lipidation at its three most frequent lipidated sites suffices for EWI-F binding, while cysteine-to-alanine CD9 mutations markedly reduced binding of EWI-F. EWI-F binding by CD9 was rescued by mutating all or, albeit to a lesser extent, only the three most frequently lipidated sites into tryptophans. These mutations did not affect the nanoscale distribution of CD9 in cell membranes, as shown by super-resolution microscopy using a CD9-specific nanobody. Thus, these data demonstrate site-specific, possibly conformation-dependent, functionality of lipidation in tetraspanin CD9 and identify tryptophan mimicry as a possible biochemical approach to study site-specific transmembrane-protein lipidation.
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