Critical residues and motifs for homodimerization of the first transmembrane domain of the plasma membrane glycoprotein CD36

Abstract

The plasma transmembrane (TM) glycoprotein CD36 is critically involved in many essential signaling processes, especially the binding/uptake of long-chain fatty acids and oxidized lowdensity lipoproteins. The association of CD36 potentially activates cytosolic protein tyrosine kinases that are thought to associate with the C-terminal cytoplasmic tail of CD36. To understand themechanismsby whichCD36mediates ligand bindingand signal transduction, we have characterized the homo-oligomeric interaction of CD36TMdomains in membrane environments and with molecular dynamics (MD) simulations. Analysis of pyreneand coumarin-labeled TM1 peptides in SDS by FRET confirmed the homodimerization of the CD36TM1peptide. Homodimerization assays of CD36 TM domains with the TOXCAT technique showed that its first TM (TM1) domain, but not the second TM (TM2) domain, could homodimerize in a cell membrane. Smallresidue, site-specific mutation scanning revealed that the CD36 TM1 dimerization is mediated by the conserved small residues Gly12, Gly16, Ala20, and Gly23. Furthermore, molecular dynamics (MD)simulation studies demonstrated thatCD36TM1exhibited a switching dimerization with two right-handed packing modes driven by the 12GXXXGXXXA20 and 20AXXG23 motifs, and the mutational effect of G16I and G23I revealed these representative conformations ofCD36TM1.This packing switch pattern ofCD36 TM1 homodimer was further examined and confirmed by FRET analysis of monobromobimane (mBBr)-labeled CD36 TM1 peptides. Overall, this work provides a structural basis for understanding the role ofTMassociation in regulating signal transduction via CD36.