The N-terminal domain of human urokinase receptor contains two distinct
regions critical for ligand recognition
JJ Pollanen
National Biotechnology Programmes, Center for Molecular Cell Biology,
Copenhagen, Denmark.
The high-affinity receptor that binds human urokinase-type plasminogen
activator (hu-PAR) is a glycosyl-phosphatidylinositol (GPI)-anchored
cell-surface glycoprotein that belongs to the Ly-6 superfamily of T-
cell-activating receptors. Binding of urokinase (u-PA) to u-PAR is
species-specific, since neither murine (mu-PAR) nor hu-PAR binds u-PA from
the other species. I designed and analyzed a series of exchanges between
hu-PAR and mu-PAR in the N-terminal first domain to which ligand-binding
function had been independently mapped. Introduction of as few as 13 murine
residues (six of 13 variables) into the N-terminal region of hu-PAR
abrogated binding to recombinant human pro-u-PA, whereas the opposite
chimera, a mu-PAR carrying six of 13 human residues, was positive for
binding. Within this region, the mu-PAR domain 1 could be minimally
humanized to bind human pro-u-PA by a substitution of as few as four of the
six nonconserved residues, thereby identifying the residues arginine-2,
lysine-7, threonine-8, and glycine-10 as important in determining binding
specificity. By alanine- scanning mutagenesis, a second recognition site
within domain 1 was discovered between residues 47 and 53, a segment that
is fully conserved between the human and the mouse receptors. Taken
together, these results provide identification of two confined subregions
within the N-terminal domain of hu-PAR critically involved in pro-u-PA
recognition.
Volume 82,
Issue 9,
pp. 2719-2729,
11/01/1993
Copyright © 1993 by The American Society of Hematology
