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Interaction of macrophage-stimulating protein with its receptor. Residues critical for beta chain binding and

A Danilkovitch1, M Miller, E J Leonard

  • 1Laboratory of Immunobiology, NCI-Frederick Cancer Research and Development Center, ABL-Basic Research Program, Frederick, Maryland 21702, USA. danilkovitch@mail.ncifcrf.gov

The Journal of Biological Chemistry
|October 9, 1999
PubMed

Insights

Macrophage-stimulating protein (MSP) has two receptor binding sites: a high-affinity site on the beta chain and a low-affinity site on the alpha chain. These sites are crucial for receptor activation and cell signaling.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Cell Signaling

Background:

  • Macrophage-stimulating protein (MSP) and hepatocyte growth factor/scatter factor (HGF/SF) are growth factors that bind to cell-surface tyrosine kinase receptors.
  • Both MSP and HGF/SF are heterodimeric proteins with alpha and beta chains, structurally similar to serine proteases.
  • The receptor binding site differs, with HGF/SF primarily using the alpha chain and MSP using the beta chain.

Purpose of the Study:

  • To investigate the structural basis of MSP beta chain's interaction with its receptor.
  • To identify critical residues involved in MSP beta chain receptor binding.
  • To characterize the binding affinities of MSP's alpha and beta chains to the receptor.

Main Methods:

  • Modeling of the MSP beta chain structure based on HGF beta chain coordinates.
  • Site-directed mutagenesis of the MSP beta chain to create specific mutants.
  • Quantitative enzyme-linked immunosorbent assay (ELISA) to determine binding affinities (EC50 values).

Main Results:

  • Modeling indicated that the Asn(682)/Glu(648) pair occupies the S1 pocket, leaving a shallow cavity for receptor interaction.
  • Mutations in this region, particularly Arg(683), significantly diminished or abolished beta chain binding.
  • The beta chain exhibited high-affinity binding (EC50 = 0.25 nM), while the alpha chain showed lower-affinity binding (EC50 = 16.9 nM).

Conclusions:

  • The MSP beta chain contains critical residues, including Arg(683), essential for high-affinity receptor binding.
  • MSP possesses two independent binding sites: a high-affinity site on the beta chain and a low-affinity site on the alpha chain.
  • These dual binding sites likely mediate receptor dimerization and subsequent activation, playing a key role in cellular responses.

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