Figure 19.3.3.2

Tsuruta, H.; Johnson, J. E.

doi:10.1107/97809553602060000700

International
Tables for
Crystallography
Volume F
Crystallography of biological macromolecules
Edited by M. G. Rossmann and E. Arnold

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International Tables for Crystallography (2006). Vol. F. ch. 19.3, p. 430 | 1 | 2 |

Figure 19.3.3.2

H. Tsuruta^a and J. E. Johnson^b ^*

^a SSRL/SLAC & Department of Chemistry, Stanford University, PO Box 4349, MS69, Stanford, California 94309-0210, USA, and ^bDepartment of Molecular Biology, The Scripps Research Institute, 10550 N. Torrey Pines Road, La Jolla, California 92037, USA
Correspondence e-mail: jackj@scripps.edu

Figure 19.3.3.2

(a) The calculated solution X-ray scattering curves from the crystal structure of Salmonella typhimorium glutamine synthetase. Glutamine synthetase is composed of 12 identical 469-residue subunits and forms a functional dodecameric assembly (PDB entry 2GLS; Yamashita et al., 1989). The single subunit was computationally isolated, and the solution scattering curves for the subunit (thin line) and the assembled form (thick line) were calculated with a 3 Å-thick hydration layer of 0.03 e Å⁻³ using CRYSOL (Svergun et al., 1995). The curves are normalized to an identical weight concentration, that is, the number concentration of the dodecamer is 1/12 of that of the subunit, giving a 12-fold increase in [I(Q = 0)] . The inset shows Guinier plots of the calculated scattering curves. The radii of gyration determined by the Guinier plot to $[Q \simeq 1.0/ R_{g}]$ (solid-line fit) for the subunit and the assembled form are 24.1 and 55.8 Å, respectively. The `extended' Guinier plots to $[Q \simeq 2.0/R_{g}]$ (circles) give 23.9 and 56.5 Å. Note that both Guinier plots are quite linear beyond $[Q \simeq 2.0/R_{g}]$ , although the Guinier approximation is theoretically valid to $[Q \simeq 1.0/R_{g}]$ . It should be noted, however, that the `extended' Guinier plot tends to give significantly smaller R_g for elongated shapes. (b) The electron distance distribution functions. The pair distribution functions $[P({\bf r})]$ were calculated from the scattering curves in (a) using GNOM (Svergun, 1992). The maximum intramolecular distance is 75 and 160 Å for the subunit and the assembled enzyme, respectively. The $[P({\bf r})]$ gives the radius of gyration as 23.6 Å for the subunit and 55.0 Å for the assembled enzyme.