DYNAMIC LIGHT-SCATTERING-STUDIES OF ALPHA(IIB)BETA(3) SOLUTION CONFORMATION

The prototypical integrin receptor, alpha(IIb)beta3, isolated from the membrane fraction of human blood platelets by solubilization in Triton X-100 (reduced) and affinity chromatography on lentil lectin-agarose, has been further purified by gel filtration chromatography in octyl glucoside to obtain the intact receptor complex in a form suitable for hydrodynamic measurements. The molecular weight [(6.0 +/- 0.2) X 10(3)] and Stokes radius (2.3 +/- 0.1 nm) of detergent micelles formed in 0.03 M octyl glucoside have been determined by classical light scattering intensity and dynamic light scattering measurements, respectively. An algorithm has been developed which explicitly considers the contribution of detergent micelles to the intensity autocorrelation function of particles suspended in detergent. This procedure has been validated with polystyrene particles of known radius, as well as with the soluble protein fibrinogen. Application of these procedures to dynamic light scattering data obtained with a(IIb)beta3 resulted in a translational diffusion coefficient (D(t)o(20,w)) of (2.78 +/- 0.31) X 10(-7) cm2 s-1, corresponding to a Strokes radius (R(s)) of 7.67 +/- 0.85 nm for the integrin/octyl glucoside complex. Light scattering intensity measurements gave a molecular weight of (2.26 +/- 0.22) X 10(5) for the polypeptide moiety of the complex, in excellent agreement with the 2.28 X 10(5) value calculated from primary structure data. As a spherical, hydrated alpha(IIb)beta3 complex, with bound detergent, would exhibit a Stokes radius of approximately 5 nm, these data indicate considerable asymmetry in the solution conformation of alpha(IIb)beta3.