Right-handed triple helix

FIGURE 6.18 Poly(Gly-Pro-Pro), a collagen-like right-handed triple helix composed of three left-handed helical chains. (Adaptedfrom Miller Scheraga, H. A., 1976, Calculation of the... 

A molecule of procollagen is formed by the association of three a chains, twisted around each other to form a right-handed triple helix of approximately 300 nm in... 

Collagen is composed of three left-handed polypeptide helices that are twisted around each other to form a right-handed triple helix (Figure 5.26). Type I collagen molecules, found in teeth, bone, skin, and tendons, are about 300 nm long and approximately 1.5 nm wide. (There are 20 major families of collagen molecules. Approximately 90% of the collagen found in humans is type I.)... 

The protein collagen, from the dermis of the skin and tendons, is composed of -30% proline and hydroxypro-line and 30% glycine. This protein has an unusual stmcture in which three chains, each with a conformation very similar to the left-handed helix of polyproline, are twisted about each other to make a right-handed triple helix. The helix has a pitch of 0.96 nm with 3.3 residues per turn thus the spiral is steeper than the a helix. The three strands are hydrogen-honded to one another between the —NH of glycine residues and the —C=0 groups of the other amino acids. 

Fig. 1 The triple helix motif. Shown is a cross-section of a right-handed triple helix made of three left-handed a chains (adapted from Ref [2]). The symbol ( ) shows one example of amino acid residues present at the same axial level and the one residue stagger between two adjacent a chains. Note the location of every third glycine residue at the center of this structural motif and the availability of the side chains of the X and Y residues at the surface. (View this art in color at www.dekker.com.)...

Fig. 4.24 Molecular structures of p-(l->3)-glucans. The subset (a) shows the repeating unit of schizophyllan, one of the p-(l->3)-glucans, for example. The natural p-(l-43)-glucans take the form of a right-handed triple helix. The subset (b) shows the helix of curdlan the helix pitch and diameter are 1.88 and 1.56 nm, respectively. Here, the circles represent glucoses. The subset (c) shows how the hydrogen bonds are formed between the adjoining glucoses.

One of the most abundant fibrous proteins in the animal body is collagen of which there are at least 11 types called type I, II etc. Collagen has a distinctive structure which occurs only in two other known proteins complement subcomponent Clq and acetylcholinesterase of electric eels. Type I collagen, the most abundant, occurring in bone, tendon, skin, teeth and arteries, contains two identical polypeptide chains called a 1(1) and a slightly different chain, a2(I). Individual chains form a left-handed helix which wind around each other to form a right-handed triple helix (Figure 4.13a). 

---