Characterization of the interaction between alpha2-macroglobulin and fibroblast growth factor-2: the role of hydrophobic interactions.
Basic fibroblast growth factor (FGF-2) is important in development, wound healing and angiogenesis. The human plasma proteinase inhibitor alpha2-macroglobulin (alpha2M) binds to and regulates the biological activity of various growth factors, including FGF-2. FGF-2 binds specifically and saturably to native alpha2M and conformationally modified alpha2M (alpha2M*); however, the KD for FGF-2 binding to alpha2M* is 10-fold lower. This study investigates the biochemical nature of the interaction between FGF-2 and alpha2M* and localizes a possible FGF-2 binding site in the alpha2M subunit. FGF-2 binding to alpha2M* was not affected by shifts in pH between 6.5 and 10; however, increasing temperature decreased the KD for this interaction. The binding affinity of FGF-2 for alpha2M* also increased with increasing ionic strength. These results are consistent with the hypothesis that hydrophobic interactions predominate in promoting FGF-2 association with alpha2M*. Consistent with this hypothesis, FGF-2 bound to a glutathione S-transferase fusion protein containing amino acids 591-774 of the alpha2M subunit (FP3) and to a hydrophobic 16-amino-acid peptide (amino acids 718-733) within FP3. Specific binding of FGF-2 to the 16-amino-acid peptide was inhibited by excess transforming growth factor-beta1. When the 16-amino-acid peptide was chemically modified to neutralize the only two charged amino acids, FGF-2-binding activity was unaffected, supporting the predominant role of hydrophobic interactions. FGF-2 presentation to signalling receptors is influenced by growth factor binding to heparan sulphate proteoglycans (HSPGs), which is electrostatic in nature. Our results demonstrate that the interactions of FGF-2 with alpha2M* and HSPGs are biochemically distinct, suggesting that different FGF-2 sequences are involved.
Mathew
Smitha
S
Department of Pathology, Box 3712, Duke University Medical Center, Durham, NC 27710, USA.
Arandjelovic
Sanja
S
Beyer
Wayne F
WF
Gonias
Steven L
SL
Pizzo
Salvatore V
SV
D001665:Binding Sites; D001667:Binding, Competitive; D016222:Fibroblast Growth Factor 2 / Q000737:chemistry* / Q000378:metabolism; D019812:Heparan Sulfate Proteoglycans / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009994:Osmolar Concentration; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D013816:Thermodynamics; D000511:alpha-Macroglobulins / Q000737:chemistry* / Q000378:metabolism
D019812:Heparan Sulfate Proteoglycans; D010446:Peptide Fragments; D000511:alpha-Macroglobulins; D016222:Fibroblast Growth Factor 2