Ligand-specific Structural Domains in the Fibroblast Growth Factor Receptor

doi:10.1074/jbc.270.17.10222

Ligand-specific Structural Domains in the Fibroblast Growth Factor Receptor (*)

From the (1) Albert B. Alkek Institute of Biosciences and Technology, Department of Biochemistry and Biophysics, Texas A & M University, Houston, Texas 77030-3303

^¶ To whom correspondence should be addressed:
Albert B. Alkek Inst. of Biosciences and Technology, Texas A & M University, 2121 W. Holcombe Blvd., Houston, TX 77030-3303.
Tel.: 713-677-7522; Fax: 713-677-7512; E-mail: wmckeeha{at}ibt.tamu.edu.

↵^§ Current address: Howard Hughes Medical Inst., Program in Molecular Medicine, University of Massachusetts Medical Center, 373 Plantation St., Worcester, MA 01605.

Abstract

Two tandem immunoglobulin-like disulfide loops (Loops II and III) linked by a short connecting sequence in the ectodomain of the fibroblast growth factor receptor kinase compose the binding sites for glycosaminoglycan and fibroblast growth factor (FGF) ligands. Alternate splicing of exons IIIb and IIIc coding for the COOH-terminal half of Loop III confers high affinity for FGF-7 or FGF-2, respectively, on the fibroblast growth factor receptor ectodomain without effect on the binding of FGF-1. Here we show that a 139-amino acid fragment composed of Loop II, the inter-Loop II/III sequence, and a short segment of the NH₂terminus of Loop III is sufficient and near the minimal requirement for binding of FGF-1, FGF-2, and FGF-7. Extension of the fragment by five additional highly conserved residues (SD(P/A)QP) within a distinct constitutive structural domain (fl1) in Loop III restricts the binding of FGF-7 without effect on FGF-1 and FGF-2. Since the presence of exon IIIc in the full-length ectodomain does not change this ligand binding profile, we suggest that alternately spliced exon IIIc plays no active role in binding of the three ligands. In contrast, exon IIIb actively abrogates the restriction on the binding of FGF-7 and concurrently lowers the affinity for FGF-2.

Footnotes

↵* This work was supported by Public Health Service Grants DK35310 and DK38639 from NIDDKD and Grant CA59971 from NCI, National Institutes of Health. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

FGF

fibroblast growth factor

FGFR

FGF receptor

PCR

polymerase chain reaction

bp

base pair(s)

Sf9

S. frugiperda cells

PBS

phosphate-buffered saline (pH 7.0)

SFR1

secreted fragment(s) of the FGFR1 extracellular domain.