 | Acta Crystallographica Section D Acta Crystallographica Section D BIOLOGICAL CRYSTALLOGRAPHY |
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![[Figure 4]](be5044fig4mag.jpg)
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Figure 4
UBA domains associate into a ninefold helix in both the UBA and UBA–UBL crystals. (a) UBA domains associate to form a ninefold helix with successive rotations of 40° and translations of 19.7 Å. The UBA domains (molecules ABCDEFGHI) are colored magenta, blue, green, yellow, red and then purple, cyan, pale green, orange so that similar colours repeating every five molecules indicate a rotation of 200°. The N-termini of the domains are labelled. Their path indicates the helical twist about the vertical axis. (b) View approximately 90° to that shown in (a) illustrating a UBL molecule (S) associated with the UBA domain (L) in the UBA–UBL complex for the chain JKLMN′O′P′Q′R′, where a prime indicates a symmetry-related molecule. The chain has been tilted about the horizontal axis in order to show the position of UBL K49. (c) The main contacts between UBL (molecule S) and UBA (molecule L) in the chain JKLMN′O′P′Q′R′ (where a prime indicates a symmetry-related molecule) are enhanced by minor contacts from UBL (S) to UBA (C) from the chain ABCDEFGHI and by minor contacts from UBL (S) to UBA (R) from the chain NOPQR. The S to R interface involves UBL residues N41, K72, S73, Q74 and UBA residues R349, L368, L369, N370 and G371. The S to C interface involves UBL residues S47, H61 and Q63 and UBA residues D346, R349, N370, G371, D372 and V373 with three hydrogen bonds: from UBL H61 side chain to UBA V373 C-terminal carboxylate, from UBL Q63 side-chain amide group to UBA D346 side-chain carboxylate and from UBL Q63 side-chain carbonyl group to UBA R349 NE group. The total molecular-surface area buried at the S–R contact is 304 Å2, at the S–C interface is 327 Å2 and at the S–L interface is 611 Å2. Similar contacts are observed for the interactions of the UBL T molecule with UBA D, UBA K and UBA A′. |
![[Figure 4]](be5044fig4.jpg)
| BIOLOGICAL CRYSTALLOGRAPHY |
ISSN: 1399-0047
