DYNAMIC LIGHT-SCATTERING INVESTIGATIONS OF HUMAN ERYTHROCYTE SPECTRIN

Dynamic light scattering measurements were performed on spectrin from human erythrocytes in 25 mM Tris buffer at pH 7.6 with 100 mM NaCl and 5 mM EDTA. Measurements were made on spectrin solutions prepared as dimers and tetramers over the temperature range from 23 to 41-degrees-C, as a function of the square of the scattering vector (K2) over the range of 0.7 X 10(10) cm-2 less-than-or-equal-to K2 less-than-or-equal-to 20 X 10(10) cm-2. Analysis of the autocorrelation functions collected for these solutions revealed the presence of two predominant motional components over the entire range of K2. Plots of the diffusion coefficients (D20) of these components, with viscosity and temperature corrected to water at 20-degrees-C, as a function of K2 indicated three rather distinct regions, flat regions at low and high K2 joined by a sloping intermediate region. At small K2 (less-than-or-equal-to 4 X 10(10) cm-2) the D20 values were (7.3 +/- 2.0) X 10(-8) cm2/s for the slow component and (20.3 +/- 2.0) X 10(-8) cm2/s for the fast component. At large K2 (greater-than-or-equal-to 10 X 10(10) cm-2) the values increased to (13.0 +/- 2.0) X 10(-8) cm2/s for the slow component and (39.4 +/- 2.0) X 10(-8) cm2/s for the fast component. In the intermediate K2 region. D20 is a linear function of K2 and appears as a transition between the low and high K2 regions. The behaviors of the fast and slow components as a function of K2 were interpreted in terms of spectrin motions by modeling spectrin heterodimers and tetramers as wormlike coils. In the low K2 region the slow [(7.3 +/- 2.0) X 10(8) cm2/s] and fast [(20.3 +/- 2.0) X 10(-8) cm2/s] components were assigned to the center of mass diffusion coefficients (D0) for tetramers (D0(tet)) and dimers (D0(dim)), respectively. In the high K2 region, the slow component was attributed to an average of D0(tet) and D0(dim). The magnitude of D20 of the fast component [(39.4 +/- 2.0) X 10(-8) cm2/s] suggested the emergence of much faster motions, surmised to be subglobal segmental motions of spectrin tetramers. These measurements supply further evidence for fluctuational segmental motions of spectrin that occur over a relatively large distance of 22-30 nm with relaxation times less-than-or-equal-to 23-mu-s.