title: Crystal Structure of a Full-Length Human Tetraspanin Reveals a Cholesterol-Binding Pocket.
abstract: 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.
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA; Department of Cancer Biology, Dana Farber Cancer Institute, Boston, MA 02215, USA.
authors.forename: Brandon
authors.initials: B
authors.lastname: Zimmerman
authors.affiliation: Departments of Computer Science and of Molecular and Cellular Physiology and Institute for Computational and Mathematical Engineering, Stanford University, Stanford, CA 94305, USA.
authors.forename: Brendan
authors.initials: B
authors.lastname: Kelly
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA; Department of Cancer Biology, Dana Farber Cancer Institute, Boston, MA 02215, USA.
authors.forename: Brian J
authors.initials: BJ
authors.lastname: McMillan
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA; Department of Cancer Biology, Dana Farber Cancer Institute, Boston, MA 02215, USA.
authors.forename: Tom C M
authors.initials: TCM
authors.lastname: Seegar
authors.affiliation: Departments of Computer Science and of Molecular and Cellular Physiology and Institute for Computational and Mathematical Engineering, Stanford University, Stanford, CA 94305, USA.
authors.forename: Ron O
authors.initials: RO
authors.lastname: Dror
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA. Electronic address: andrew_kruse@hms.harvard.edu.
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Kruse
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA; Department of Cancer Biology, Dana Farber Cancer Institute, Boston, MA 02215, USA; Department of Pathology, Brigham and Women's Hospital, Boston, MA 02115, USA. Electronic address: stephen_blacklow@hms.harvard.edu.
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Blacklow
mesh_terms: D001665:Binding Sites; D002784:Cholesterol / Q000378:metabolism*; D018360:Crystallography, X-Ray; D006801:Humans; D008956:Models, Chemical; D056004:Molecular Dynamics Simulation; D060225:Tetraspanin 28 / Q000737:chemistry* / Q000378:metabolism*
chemical_list: C554798:CD81 protein, human; D060225:Tetraspanin 28; D002784:Cholesterol
keywords: CD19; CD81; X-ray crystallography; membrane protein; protein structure; protein trafficking