Characterization of the stromal cell-derived factor-1alpha-heparin complex

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Interactions

Background:

• Chemokine binding to glycosaminoglycans (GAGs) is vital for chemokine functions.
• Stromal cell-derived factor-1alpha (SDF-1alpha), a CXC chemokine, exhibits anti-HIV activity and interacts with GAGs.
• Previous studies identified a heparin recognition sequence (BBXB) in SDF-1alpha.

Purpose of the Study:

• To investigate the structural basis of SDF-1alpha binding to heparin.
• To identify key amino acid residues and GAG features involved in SDF-1alpha-heparin interactions.
• To elucidate the role of specific sulfate groups and oligosaccharide length in binding.

Main Methods:

• Site-directed mutagenesis of SDF-1alpha.
• Surface plasmon resonance (SPR) binding assays.
• Analysis of binding with modified heparin (desulfated, oligosaccharides, fragments) and competition assays.
• GRID calculations and molecular docking studies based on SDF-1alpha crystal structure.

Main Results:

• Lys-24 and Lys-27 are essential for SDF-1alpha binding to heparin, with Arg-41 and Lys-43 playing supporting roles.
• The N-terminal Lys-1 is involved in complex formation and is critical for receptor activation.
• Efficient binding requires heparin oligosaccharides of at least 12-14 monosaccharide units, with 2-O- and N-sulfate groups being crucial.
• Molecular modeling revealed a precise fit of heparin within a crevice formed by key residues on the SDF-1alpha dimer.

Conclusions:

• SDF-1alpha utilizes a specific binding site involving multiple basic residues, particularly Lys-1, Lys-24, Lys-27, and Arg-41, for heparin interaction.
• Heparin's structural features, including size and sulfation pattern, significantly influence binding affinity.
• Understanding these interactions provides insights into SDF-1alpha's biological functions and potential therapeutic applications.