C-helix

Top right) The tetramer viewed from the top. The transition segment between the N-helix and the C-helix is shown in yellow and blue and the C-terminus is shown in green and purple. The hydrophobic strips are in the center and the N-helices are on each side. The tetramer has 2-fold symmetry about each of the three axes. 

Identification of Neoxanthin The 9-cis Requirement for a Xanthophyll in the C-Helix Domain... 

There is a second long interface stretching between the threefold and fourfold axes, involving both hydrophobic and hydrophilic interactions. Close to the threefold axis is an intersubunit salt bridge between Asp-139 of subunit I and His-128 in III, which links the N-terminal end of helix D (III) to a position near the kink in helix D (I). Further along the interface, N-terminal residues 6-12 of subunit III make several interactions with the C-helix of subunit I, including several which are mediated... 

Figure 5.44 Elastic deformations of CDLC helices, (a) Low-pitch helix free from external force attached to glass rod at one end, (b) same helix attached at both ends and slightly extended, and (c) helix extended beyond 16.5° and allowed to come to equilibrium with respect to the straightening transition (helix ends are off screen). Reprinted from Ref. 163 with permission of the author. Copyright 2001 by the American Physical Society.

Fig. 3 Comparison of erlotinib (thin lines) with lapatinib (thick lines). Tbe C-helix is portrayed as a backbone ribbon, and tbe side chain of Met742 is explicitly shown...

Fig. 14.1. Ribbon structure (magenta) of the phosphorylase kinase crystal structure 2PHK (20) bound with ATP (green carbons, colored by atom type) and substrate peptide (light blue ribbon). The N- and C-terminal lobes are highlighted the hinge region is shown in cyan, the a-C helix in gray, and the -loop in orange.

Columns index the state of amino acid residue /, rows index the state of amino acid residue i-1, and the order of indexing is coil (c), helix (h). 

Fig. 2.6. The dynamic domains of goat a-lactalbumin, domain 1 (dark gray) and domain 2 (light gray), and the screw axis of the interdomain motion [24]. The C-helix is involved in domain 2 and moves together with the Ca2+-binding site and the 13-domain. Reproduced with permission from [24]...

The C helix forms the back wall of the ATP-binding site [9]. It contains a conserved glutamic acid residue (Glu-52), which is of key importance in the phosphotransfer process, forming an ion pair with Lys-33 (Figure 7.3). Lys-33, which is buried deep in the ATP-binding cleft, makes a crucial contact with the a,P-phosphate oxygens, positioning them so as to facilitate the y-phosphoryl transfer [4 (i)]. 

In the absence of cyclin-A, the C helix is twisted and the conserved Glu-51 residue on its surface faces the solvent and is unable to coordinate with Lys-33, which instead coordinates with Asp-145. The torsion angles of Phe-146 and Asp-145 in the DFG motif are typical for an inactive kinase [15] (Table 7.2) and show that the orientation of Asp-145 is unfit for catalysis. 

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