 | Acta Crystallographica Section D Acta Crystallographica Section D BIOLOGICAL CRYSTALLOGRAPHY |
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![[Figure 5]](ts5040fig5mag.jpg)
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Figure 5
Crystal packing in the orthorhombic complex II crystals reveal them to be `type 1' crystals. In both crystal forms the cell contains four molecules. The crystal contains zones parallel to the ab plane consisting of transmembrane helix regions, suggesting that the crystals are stacks of two-dimensional membrane crystals as described by Michel (his `type 1' crystals). Each such membranous zone has complex II molecules inserted alternately from opposite sides. (a) P212121 crystals: the unit cell spans two such membranes related by the twofold screw axis along c (perpendicular to the membrane). Adjacent molecules within each membrane are related by the screw axes along a and b, as is often observed in two-dimensional crystals of membrane proteins. Between adjacent membrane zones are two zones of extrinsic domains, one from each membrane, resulting in the long c axis of this crystal form. (b) P21 crystals. The unit cell spans two membranes related by the twofold screw axis along b. The pseudo-twofold axis about c is within the membrane plane, relating adjacent up- and down-oriented molecules such as the red and blue molecules depicted. Extrinsic domains from two adjacent membranes interdigitate, allowing the membranes to stack more closely and resulting in the shorter longest axis of this crystal form. Along the c axis (perpendicular to the plane of the picture) there is only translational symmetry; that is, more molecules exactly behind those depicted. |
![[Figure 5]](ts5040fig5.jpg)
| BIOLOGICAL CRYSTALLOGRAPHY |
ISSN: 1399-0047
