The dimerization of PSGL-1 is driven by the transmembrane domain via a leucine zipper motif

: P-selectin glycoprotein ligand-1 (PSGL-1) is a homodimeric mucin ligand that is important to mediate the earliest adhesive event during an inflammatory response by rapidly forming and dissociating the selectin-ligand adhesive bonds. Recent research indicates that the noncovalent associations between the PSGL-1 transmembrane domains (TMDs) can substitute for the C320-dependent covalent bond to mediate the dimerization of PSGL-1. In this article, we combined TOXCAT assays and molecular dynamics (MD) simulations to probe the mechanism of PSGL-1 dimerization. The results of TOXCAT assays and Martini coarse-grained molecular dynamics (CG MD) simulations demonstrated that PSGL-1 TMDs strongly dimerized in a natural membrane and a leucine zipper motif was responsible for the noncovalent dimerization of PSGL-1 TMD since mutations of the residues that occupied a or d positions in an (abcdefg)n leucine heptad repeat motif significantly reduced the dimer activity. Furthermore, we studied the effects of the disulfide bond on the PSGL-1 dimer using MD simulations. The disulfide bond was critical to form the leucine zipper structure, by which the disulfide bond further improved the stability of the PSGL-1 dimer. These findings provide insights to understand the transmembrane association of PSGL-1 that is an important structural basis for PSGL-1 preferentially binding to P-selectin to achieve its biochemical and biophysical functions.