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Figure 5.
Figure 5. Interactions of inter-TPR turns among homologous TPR
domains. Interactions between adjacent TPR units are mediated by
hydrogen bonding between Pro (position 32, i) and Trp (position
4 in the next helix, i+6). Proline at position 32 is generally
highly conserved for this purpose. Therefore, the position 4 is
generally occupied by Trp, Tyr, and His.[34] A detailed view of
an inter-TPR turn is shown and is representative of several TPR
domains. (A) Inter-TPR turn of CTPR3[34] and the turn1 of NrfG.
In CTPR3, the backbone carbonyl of Pro74 interacts with the
side-chain nitrogen of Trp80. In NrfG, the backbone carbonyl of
Pro70 interacts with the side-chain nitrogen of Trp76. (B)
Inter-TPR turns of NrFG. Although Pro at position 32 of the turn
2 and 4 is substituted by Gly104 and Ser176, respectively,
Tyr110 and Arg181 interact with Gly110 and Ser176, respectively,
to stabilize the turns. (C) Inter-TPR turn with no hydrogen
bond. Interestingly, Leu320 (OGT) and Leu147 (NrfG) are placed
at position i+6 and thus they cannot form hydrogen binds in the
turns of OGT and NrfG. The turn between TPR9 and TPR10 in OGT is
-142°, whereas that of turn3 between TPR2 and TPR3 of NrfG
is -139°, which are both lower angles than the packing
angles of other TPR domains with hydrogen bonds at the turns
(also see Table II).
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