Crystal Structure of a Full-Length Human Tetraspanin Reveals a Cholesterol-Binding Pocket

Cell. 2016 Nov 3;167(4):1041-1051.e11. doi: 10.1016/j.cell.2016.09.056. Epub 2016 Oct 27.


Tetraspanins comprise a diverse family of four-pass transmembrane proteins that play critical roles in the immune, reproductive, genitourinary, and auditory systems. Despite their pervasive roles in human physiology, little is known about the structure of tetraspanins or the molecular mechanisms underlying their various functions. Here, we report the crystal structure of human CD81, a full-length tetraspanin. The transmembrane segments of CD81 pack as two largely separated pairs of helices, capped by the large extracellular loop (EC2) at the outer membrane leaflet. The two pairs of helices converge at the inner leaflet to create an intramembrane pocket with additional electron density corresponding to a bound cholesterol molecule within the cavity. Molecular dynamics simulations identify an additional conformation in which EC2 separates substantially from the transmembrane domain. Cholesterol binding appears to modulate CD81 activity in cells, suggesting a potential mechanism for regulation of tetraspanin function.

Keywords: CD19; CD81; X-ray crystallography; membrane protein; protein structure; protein trafficking.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Binding Sites
  • Cholesterol / metabolism*
  • Crystallography, X-Ray
  • Humans
  • Models, Chemical
  • Molecular Dynamics Simulation*
  • Tetraspanin 28 / chemistry*
  • Tetraspanin 28 / metabolism*


  • CD81 protein, human
  • Tetraspanin 28
  • Cholesterol