SAXS analysis of eAPP fragments and their complexes.

The maximum estimated error in the radius of gyration (R g) is ±2 Å. The maximum estimated error in maximum dimension (Dmax) is ±10 Å. Both values were calculated with the program GNOM [31]. The relative mass was calculated as the ratio of the apparent mass of the protein (MWcalc) to the expected mass derived from the protein sequence (MWseq). The molecular weight derived from the protein sequence is 52-kDa for TRX-eAPP290–624, 45-kDa for eAPP230–624, and 90-kDa for MBP-eAPP230–624. For globular, non-interacting proteins, the apparent mass can be estimated by comparing the extrapolated scattering of the sample at zero scattering angle (I(0)) to that of the reference protein albumin and the eAPP fragment dimerwhere subscripts un and ref refer to the sample and the reference protein [56]. The error is the calculated mass is primarily due to the uncertainty in the estimation of the concentrations. The maximum error was determined experimentally by replicates of within a much larger set of experiments [18] to be ±0.2, where the maximum error determines the range of values for which p51.