The scaled mobilities, Ms, for the spin-labeled sites within syt1C2AB that are located in the linker region or in the 8th β-strand of C2A. Values of Ms were calculated from the central linewidth of the EPR spectrum using Eq. 1. Aqueous values are shown in gray, values for syt1C2AB bound to POPC:POPS (75:25) vesicles are shown in black. When bound to lipid bilayers, there is a small decrease in the scaled mobility at some sites. Some of this decrease is likely due to a decrease in protein rotation and attachment of C2A and C2B upon membrane binding. Several sites show larger changes upon binding, which may indicate changes in local structure or dynamics upon membrane association (see text).