1. The structure of OmpF porin in a tetragonal crystal form
SW Cowan, RM Garavito, JN Jansonius, JA Jenkins, R Karlsson, N König, EF Pai, RA Pauptit, PJ Rizkallah, JP Rosenbusch, G Rummel, T Schirmer 
Structure 
Volume 3, Issue 10, Pages (October 1995)
DOI: /S (01)

2. Figure 1
Schematic diagram of the topology of OmpF porin showing β strands as rectangles and α helices (in loops three and five) as consecutive circles. Loops (at the top) and turns (at the bottom) are labelled. A blue background indicates the regions involved in subunit interactions. Residues involved in crystal contacts in the P42 crystal form are shown in dark blue (inter-tetrahedron) and yellow (intra-tetrahedron). Crystal contacts in the P321 crystal form are indicated by green circles.
Structure 1995 3, DOI: ( /S (01) )

3. Figure 2
Stereo diagram of the superimposed Cα traces of OmpF porin monomers from the tetragonal (black) and trigonal (red) crystal forms. In this view, the long loops are at the top (the ‘rough’ end) of the barrel and the short turns are at the bottom (the ‘smooth’ end). The molecular threefold axis (not shown) runs vertically in front of the monomer.
Structure 1995 3, DOI: ( /S (01) )

4. Figure 3
Schematic diagram of the symmetry in the P42 crystals (see also Figure 4 of [23]). Crystallographic symmetry elements are represented by black symbols, non-crystallographic twofold axes in dark blue and non-crystallographic threefold axes in light blue. The asymmetric unit is made up of two trimers (coloured green and red) and the monomers are labelled A to F.
Structure 1995 3, DOI: ( /S (01) )

5. Figure 4
Crystal packing of OmpF porin in the tetragonal crystal form. (a) Stereo diagram of the Cα traces of a tetrahedron composed of four OmpF porin trimers (viewed along c as in Figure 3). The two local twofold axes are shown in red and the four local threefold axes in yellow. The crystallographic twofold axis (not shown) runs along the viewing direction through the centre of the tetrahedron. (b) View along the ab diagonal of the unit cell showing the arrangement of tetrahedra within the tetragonal crystals. The tetrahedra are part of two different networks (shown in green and orange) that are separated from each other by more than 10 å (see text). Successive application of the crystallographic 42 screw axis to a green and an orange tetrahedron results in two helices (with a pitch of 2c) that are staggered with respect to each other by one cell dimension c.
Structure 1995 3, DOI: ( /S (01) )

6. Figure 4
Crystal packing of OmpF porin in the tetragonal crystal form. (a) Stereo diagram of the Cα traces of a tetrahedron composed of four OmpF porin trimers (viewed along c as in Figure 3). The two local twofold axes are shown in red and the four local threefold axes in yellow. The crystallographic twofold axis (not shown) runs along the viewing direction through the centre of the tetrahedron. (b) View along the ab diagonal of the unit cell showing the arrangement of tetrahedra within the tetragonal crystals. The tetrahedra are part of two different networks (shown in green and orange) that are separated from each other by more than 10 å (see text). Successive application of the crystallographic 42 screw axis to a green and an orange tetrahedron results in two helices (with a pitch of 2c) that are staggered with respect to each other by one cell dimension c.
Structure 1995 3, DOI: ( /S (01) )

7. Figure 5
B-factor analysis as a function of residue number. The secondary structure of OmpF is represented beneath the plot by a step function: low=β strands; medium=turns (at the smooth end of the barrel) and high=loops (at the rough end of the barrel). (a) Grouped main-chain B factors (in å2) of the model of OmpF in the tetragonal crystal form. (b) Differences between the temperature factors of the trigonal (P321) and tetragonal (P42) crystal form models of porin (ΔB=B[trigonal]–B[tetragonal]) in å2. A positive value indicates that the temperature factor is lower in the P42 model. Large differences are found only for the loop regions at the rough end of the barrel and for residues from the smooth rim of the barrel.
Structure 1995 3, DOI: ( /S (01) )

8. Figure 5
B-factor analysis as a function of residue number. The secondary structure of OmpF is represented beneath the plot by a step function: low=β strands; medium=turns (at the smooth end of the barrel) and high=loops (at the rough end of the barrel). (a) Grouped main-chain B factors (in å2) of the model of OmpF in the tetragonal crystal form. (b) Differences between the temperature factors of the trigonal (P321) and tetragonal (P42) crystal form models of porin (ΔB=B[trigonal]–B[tetragonal]) in å2. A positive value indicates that the temperature factor is lower in the P42 model. Large differences are found only for the loop regions at the rough end of the barrel and for residues from the smooth rim of the barrel.
Structure 1995 3, DOI: ( /S (01) )

9. Figure 6
Example of model bias removal achieved by cyclic averaging. The region around Tyr157 is shown, at the outer surface of the porin molecule. (a) Cyclically averaged electron density with the starting model superimposed. (b) Final model and corresponding 2Fo−Fc map. Density to the right of the tyrosine residue is of similar strength to the protein density and presumably represents part of a detergent alkyl chain.
Structure 1995 3, DOI: ( /S (01) )

10. Figure 6
Example of model bias removal achieved by cyclic averaging. The region around Tyr157 is shown, at the outer surface of the porin molecule. (a) Cyclically averaged electron density with the starting model superimposed. (b) Final model and corresponding 2Fo−Fc map. Density to the right of the tyrosine residue is of similar strength to the protein density and presumably represents part of a detergent alkyl chain.
Structure 1995 3, DOI: ( /S (01) )

11. Figure 7
Difference density of the iridium soak. The highest maxima of the map (yellow ellipses) are superimposed on a schematic diagram demonstrating the centro-symmetric relationship of the heavy atoms in the unit cell. The white lines join adjacent heavy-atom binding sites within a tetrahedron (density is only shown for half of the unit cell). The blue cross (at X,N,Z=1/4, 1/4, 1/4) represents one of the centres of symmetry through which all of the heavy-atom binding positions in the crystal are related. The Cα trace of one tetrahedron of trimers is shown to demonstrate the relationship between the heavy-atom binding sites and the protein.
Structure 1995 3, DOI: ( /S (01) )