THE AMINO-TERMINAL IMMUNOGLOBULIN-LIKE DOMAIN OF ACTIVATED LEUKOCYTE CELL-ADHESION MOLECULE BINDS SPECIFICALLY TO THE MEMBRANE-PROXIMAL SCAVENGER RECEPTOR CYSTEINE-RICH DOMAIN OF CD6 WITH A 1 1 STOICHIOMETRY/
Ma. Bowen et al., THE AMINO-TERMINAL IMMUNOGLOBULIN-LIKE DOMAIN OF ACTIVATED LEUKOCYTE CELL-ADHESION MOLECULE BINDS SPECIFICALLY TO THE MEMBRANE-PROXIMAL SCAVENGER RECEPTOR CYSTEINE-RICH DOMAIN OF CD6 WITH A 1 1 STOICHIOMETRY/, The Journal of biological chemistry, 271(29), 1996, pp. 17390-17396
Activated leukocyte cell adhesion molecule (ALCAM) was recently identi
fied as a ligand for CD6, a signaling receptor expressed on T cells, a
subset of B cells, and some cells in the brain. Receptor-Ligand bindi
ng assays, antibody blocking experiments, and examination of the tissu
e distribution of these two cell surface proteins suggest that CD6-ALC
AM interactions play an important role in mediating the binding of thy
mocytes to thymic epithelial cells and of T cells to activated leukocy
tes. Presently, the details of CD6-ALCAM interactions and of signaling
through CD6 are unknown, A series of truncated human ALCAM and CD6 im
munoglobulin fusion proteins were produced and tested in different bin
ding assays to analyze ALCAM-CD6 interactions in more detail, In this
study, we report that the amino-terminal Ig-like domain of human ALCAM
specifically binds to the third membrane-proximal scavenger receptor
cysteine-rich (SRCR) domain of human CD6. Using thrombin-cleaved Ig fu
sion proteins containing single or multiple ALCAM or CD6 domains, we w
ere able to determine that the stoichiometry of the interaction betwee
n the amino-terminal ALCAM domains and the membrane-proximal CD6 SRCR
domain is 1:1. These results provide the first example of an Ig-like d
omain mediating an interaction with an SRCR domain.