Amino-terminal basic residues of Src mediate membrane binding through electrostatic interaction with acidic...

Area of Science:

• Biochemistry
• Cell Biology
• Molecular Biology

Background:

• pp60src (Src) is a tyrosine kinase involved in cell signaling.
• Membrane association is critical for Src kinase activity and function.
• The myristoylated amino terminus of Src is known to mediate membrane targeting.

Purpose of the Study:

• To elucidate the specific molecular interactions responsible for Src membrane targeting.
• To determine the role of basic residues in the Src amino terminus for lipid bilayer binding.
• To investigate the contribution of electrostatic interactions to Src membrane localization and oncogenic potential.

Main Methods:

• In vitro lipid bilayer binding assays using vesicles of varying phospholipid compositions (phosphatidylcholine/phosphatidylserine).
• Characterization of binding affinities (Kd) for wild-type and mutant Src proteins.
• In vivo studies using Src mutants to assess membrane binding and cellular transformation.

Main Results:

• Src binds 2500-fold more strongly to acidic phospholipid bilayers (PC/PS) than neutral bilayers, with an apparent Kd of 6 x 10(-7) M.
• Six basic residues in the amino terminus are essential for high-affinity membrane binding; mutations to asparagine significantly reduce binding affinity (apparent Kd of 2 x 10(-3) M).
• Transforming v-Src and activated c-Src (Y527F) show enhanced binding to acidic bilayers.

Conclusions:

• High-affinity membrane targeting of Src is mediated by electrostatic interactions between basic residues in its amino terminus and acidic phospholipids.
• This positive charge-driven interaction is sufficient to account for Src membrane localization.
• The findings highlight the importance of specific amino-terminal residues for Src function, membrane association, and cellular transformation.