FIGURE 13.

Greater flexibility of the L-selectinN138G hinge increases tethering by enhanced rotational diffusion. (a, b) The tether-rate dependence for L-selectin or L-selectinN138G on the product $r\stackrel{.}{\gamma }$ of the microsphere radius r and the wall shear rate $\stackrel{.}{\gamma }$. The data were measured by the same method as described in Fig. 1a legend and represent the mean ± the SD from three experiments. The microspheres were coated with 750 molecules μm⁻² of either L-selectin or L-selectinN138G, except in one case in (b), where they were coated with 1500 molecules μm⁻² of L-selectinN138G (blue squares). The flow chamber floor in (a) was coated with PSGL-1 at either 120 (red triangles and green diamonds) or 240 (blue squares) molecules μm⁻². The flow chamber floor in (b) was coated with a constant density of 6-sulfo-sLe^x. (c) Optimal $r\stackrel{.}{\gamma }$ (peak locations of the p_ad/(m_rm_lr) vs. $r\stackrel{.}{\gamma }$ curves) vs. microsphere diffusivity k_BT/(6πμr)of 3-μm radius microspheres bearing L-selectin (red triangle) or L-selectinN138G (green diamond) tethering to PSGL-1 were plotted for comparison. The open circles are microsphere data from Fig. 4a for calibration. (d) Maximum p_ad/(m_rm_lr) vs. molecular diffusivity k_BT/(6πμl) data for L-selectin bearing microspheres tethering to PSGL-1 from Fig. 4c were replotted to provide calibration (open circles), which assumed the characteristic length for molecular diffusion as l = 100 nm. The same l value was used for the L-selectin datum (red triangle), which matched the calibration curve well. The molecular diffusivity for L-selectinN138G is predicted to be larger. Using the measured maximum p_ad/(m_rm_lr) value, the L-selectinN138G datum point (green diamond) was located at the intercept of y = [p_ad/(m_rm_lr)]_max (green dashed horizontal line) and the extrapolation of the calibration curve (red line). The increased molecular diffusivity for L-selectinN138G could be calculated from the x-axis value of this datum point (green dashed vertical line), which is 85% over the value for L-selectin. Reproduced from Lou et al.⁸