Asx-turn

All turns have been classified according to Crawford et al. 90) and Richardson 91). One subunit exhibits 26 reverse turns (10 type 1, 5 type 1, 10 type 2, and 1 type 2 ) three reverse, type-1 turns associated with a-helices three near-reverse turns (one type 1 and two type 2), and three open turns. The preference of glycine at position 3 in the turn is very pronounced. There are three cis-proline turns 92) and one Asx turn (93), which displays conventional geometry. The cis-prolines have no unusual function in the structure. 

Glycosylation-induced conformational switching from an (a) Asx-turn to a (b) type I j3-turn [68]... 

Figure 5.58 Conformation and activation of asparagines, (a) P-Tum and ASX turn (b) activated forms of the amide.

To complement H-NMR studies, an extended molecular dynamics simulation of 58 was carried out. The starting geometry for 58 was generated using coordinates taken from the partially helical, C-terminal decapeptide portion (residues 27-36) of the NPY model shown in Plate 13. The residues corresponding to Thr-32 and Gln-34 were replaced with Tyr and Leu, respectively, and subjected to an unconstrained molecular dynamics simulation. The structures obtained from this simulation (a representative structure is shown in Plate 15b) share several important features with those observed by H-NMR, specifically the formation of an Asx turn and close association of the aromatic tyrosine rings. 

Figure 8 (a) Covalently modified analogs of the Asx-turn motif, (b) Disulfide and lactam dimers disulfide dimers are equal mixtures of parallel and antiparallel isomers. Dpr, (L)-2,3-diaminopropionic acid. 

Abbadi, A., Mcharfi, M., Aubry, A., Prelimat, S., Boussard, G. Marraud, M. (1991) Involvement of side functions in peptide structures The Asx turn. Occurrence and conformational aspects. J. Am. Chem. Soc. 113, 2729-2735. 

Figure 15 Formation of turns by functional groups on side chains forming hydrogen bonds to main-chain groups for (a) serine and (b) aspartate (the Asx turn ). Note the similarity to the normal turns in polypeptide chains shown in Figure 10...

The ASX-Turn. This type of structure, with hydrogen tending between the... 

In Older to constrain a pepdde into an Asx-turn another approach must be used. The pepdde analog 4 is constrained by a sidechain-backbone cyclizadon into the desired conformadon. One and two dimensional NMR confirm that... 

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