The value of the R g was derived from the Guinier approximation (Guinier and Fournet 1955) : I(q) = I(0) exp(Àq 2 R g 2 /3), where I(q) is the scattered intensity and I(0) is the forward scattered intensity. The R g and I(0) are inferred, respectively, from the slope and the intercept of the linear fit of Ln[I(q)] versus q 2 at low q values (q R g < 1.0). The distance distribution function P(r) is the histogram of all the interatomic distances within a molecule. This function also provides the maximum dimension D max of the molecule, which is defined as the point where P(r) becomes zero. The P(r) function was calculated by the Fourier inversion of the scattering intensity I(q) using GNOM (Svergun 1992) and GIFT (Bergmann et al. 2000) on the entire scattering spectra.