Te. Gray et al., ASPARAGINE-344 IS A KEY RESIDUE FOR LIGAND-BINDING IN KERATINOCYTE GROWTH-FACTOR RECEPTOR, Biochemistry, 35(49), 1996, pp. 15640-15645
The membrane proximal, immunoglobulin- (Ig-) like domain 3 of KGFR sho
ws significant sequence similarity to the Ig light chain variable (V)
domain. According to our model, based on this similarity, the F-G loop
in KGFR corresponds to the complementarity determining region (CDR) 3
of the Ig V domain. The F-G loop in the membrane proximal domain of t
he keratinocyte growth factor receptor has previously been shown to pa
rticipate in determining the FGF ligand binding specificity of KGFR [G
ray, T. E., Eisenstein, M., Shimon, T., Givol, D., & Yayon, A. (1995)
Biochemistry 34, 10325-10333]. Here, we report the effects of addition
al mutations in this F-G loop, Both a single mutant KGFR Q(348)-->I an
d a double mutant KGFR Q(348)-->I, Q(351)-->H are found to have relati
vely mild effects on ligand binding, as was previously found for three
other F-G loop mutant receptors. In contrast, a single mutation N-344
-->A in the F-G loop of KGFR is sufficient to abolish essentially all
affinity of this receptor for its primary ligand KGF, while some affin
ity for aFGF is retained, Asparagine-344 is, therefore, essential for
ligand binding by KGFR. We discuss the likelihood of this effect being
due to global or local structural changes or to the removal of a spec
ific interaction with the ligand, in relation to various known and mod
el structures. Taking into account the mild effects of other mutations
in the region and various other considerations, we tend to favor the
idea that asparagine-344 is a key residue in determining the local con
formation of the F-G loop.