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Structural characterization of a dimerization interface in the CD28 transmembrane domain

Hongyi Wu1, Ruiyu Cao1, Maorong Wen2

  • 1State Key Laboratory of Molecular Biology, Shanghai Institute of Biochemistry and Cell Biology, Center for Excellence in Molecular Cell Science, Chinese Academy of Sciences, Shanghai 200031, China; University of Chinese Academy of Sciences, Beijing 100049, China.

Structure (London, England : 1993)
|April 9, 2022
PubMed

Insights

The CD28 transmembrane helix (TMH) unexpectedly forms tetramers, not dimers. Specific mutations disrupt TMH assembly, impacting CD28 function in immune responses.

Area of Science:

  • Immunology
  • Structural Biology
  • Biophysics

Background:

  • CD28 is vital for T cell activation and immune response regulation.
  • The CD28 transmembrane helix (TMH) is implicated in receptor assembly and activity.
  • Structural data on the CD28-TMH is currently lacking.

Purpose of the Study:

  • To structurally characterize the dimeric helix-helix packing of CD28-TMH.
  • To investigate the role of specific motifs in CD28-TMH assembly and function.

Main Methods:

  • Nuclear magnetic resonance (NMR) technology was employed.
  • Structural determination of wild-type and mutant CD28-TMH in lipid bicelles.
  • Functional assays in cells to assess CD28 enhancement.

Main Results:

  • Wild-type CD28-TMH forms stable tetramers, not dimers, in lipid bicelles.
  • A conserved GxxxA motif at the dimerization interface is crucial for TMH assembly.
  • Mutations in the GxxxA motif disrupt TMH assembly and reduce CD28-mediated enhancement.
  • A proposed YxxxxT motif did not affect dimerization but influenced CD28 activity.

Conclusions:

  • The CD28-TMH exhibits tetrameric assembly, challenging previous assumptions.
  • The GxxxA motif plays a key role in CD28-TMH oligomerization and function.
  • CD28 transmembrane domain regulation of signaling is complex and multifaceted.

Keywords:
CD28 transmembrane domainNMR structuredimer interfacefunctional mutagenesis

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