Polyproline type II helices

Figure 14.1 Each polypeptide chain in the collagen molecule folds into an extended polyproline type II helix with a rise per turn along the helix of 9.6 A comprising 3.3 residues. In the collagen molecule three such chains are supercoiled about a common axis to form a 3000-A-long rod-like molecule. The amino acid sequence contains repeats of -Gly-X-Y- where X is often proline and Y is often hydroxyproline. (a) Ball and stick model of two turns of one polypeptide chain.

Figure 14.2 Models of a collagen-like peptide with a mutation Gly to Ala in the middle of the peptide (orange). Each polypeptide chain is folded into a polyproline type II helix and three chains form a superhelix similar to part of the collagen molecule. The alanine side chain is accommodated inside the superhelix causing a slight change in the twist of the individual chains, (a) Space-filling model, (b) Ribbon diagram. Compare with Figure 14.1c for the change caused by the alanine substitution. (Adapted from J. Bella et al.. Science 266 75-81, 1994.)...

The binding of interaction domains to their targets is not always dependent on post-translational modifications. Notably, a number of modules, including SH3, WW and EVHl domains, recognize short proline-rich motifs that adopt a polyproline type II helix, and these interactions... 

Fig. 1. The polyproline type II helix is an all-tram left-handed helix, whose structure can be represented as a triangular prism. The three consecutive side chains that account for one turn of the PPII helix occupy a different edge of the prism.

The polyproline type II helix is that adopted by the polypeptide chains of collagen. It has 3.0 residues per turn and a helix pitch of 0.94 nm. 

Collagen-like Polyproline type II (A-y-Gly) repeat Helix nucleation followed by zippering fiber formation still a significant challenge Perpendicular... 

The crystal structure of the peptide substrate-binding domain (140—245 of 517 residues of human al subunit) of the human type I enzyme forms 2.5 tetratricopeptide (TPR) repeat domains with five a helices (PDB accession number ITJC). The organization of tyrosine residues is suggested to be key to its interaction with the substrate peptide in a polyproline II helix. The TPR motif is composed of a 34 amino acid repeated a helical motif, and is typically involved in protein-protein interactions. The tandem repeats of TPR motifs are found in many proteins related to chaperone, cell cycle, transcription, and protein transport... 

Despite different sequences and repetitive motives, all gliadins have the same secondary structure of loose spirals which are a balanced compromise between the p-spiral and poly-L-proline structure (polyproline helix II) (Parrot et al., 2002), the balance is dependent on temperature, type of solvent, and hydration level (Miles et al., 1991). Similar sequences can be found in other proteins, mainly animal proteins such as elastin and collagen, and they are responsible for particular biomechanical properties connected to reverse P-spirals or p-sheet structures (Tatham and Shewry, 2000). 

Figure 5 CoUagen building blocks, (a) A polyproline II type helix (b) A coUagen triple helix assembled from three polyproline n strands. (Reproduced from Ref. 1. American Chemical Society, 2008.)...

Other types of structures are represented by polyproline I and II. These two structures correspond to the fact that the peptide bond can exist either in the cis co = 0°) or in the trans form (o> = 180°). Polyproline I, in which the peptide unit is in the cis form, is twisted in a rigid right-handed threefold helix n = 3.3, h = 2.2 A). Polyproline II, which corresponds to the trans form of the peptide bond, is a left-handed, three-fold helix (n = 3,... 

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