3.1. Size and global shape of PV2
The size and global shape of the quaternary structure of native PV2
were studied by means of SAXS experiments. The data obtained were
normalized for protein concentration and depicted in Fig. 1A. A gyration
radius of 44±1 Å was obtained from the Guinier plot (inset in Fig. 1A).
The Kratky plot has the typical bell-shaped form expected for globular
proteins (Fig. 1B). Fig. 1C shows the pair distance distribution P(r)
obtained using the regularized Fourier Transformmethod implemented
in the program GNOM 4.5 [25]. The P(r) obtained for native PV2 shows
a maximum at 44 Å with a well defined Dmax=130 Å compatible
with an anisometric particle. A low-resolution model for native PV2
was obtained using Simulated Annealing Algorithms implemented
in the program DAMMIN [22]. The final model, obtained by averaging
16 independently calculated models using the algorithms implemented
in the program package DAMAVER [24], is depicted in Fig. 2.
This ab initio dummy atom model fitted satisfactorily with the experimental
scattering intensity data (Fig. 1C). Image analysis of
TEM data helped to obtain the size distribution curve of these
particles. The particle size distributions for the protein are shown as a
histogram where a maximum around 137 Å can be observed (Fig. 1D
and Fig. 2S).
Fig.