Glycine packing arrangement

Figure 27. Packing arrangement of the a-form of glycine, viewed along the a axis. The layer of molecules in set 1 has the C-H (re) bond directed along + b in set 2 the equivalent C-H (si) bond is directed along —b.

Fig. 11.7. Packing arrangement of the a-form of glycine a Top view of the hydrogen-bonded bilayer...

Other fibrous proteins contain extensive regions of pleated sheets. The fibers spun by a silkworm, for example, are made almost entirely of fibroin, a protein composed primarily of just three amino acids glycine (45%), alanine (30%), and serine (12%). Each chain of fibroin contains extensive regions where a sequence of six amino acids occurs repeatedly . .. -Gly-Ser-Gly-Ala-Gly-Ala-. .. Notice that every other amino acid is glycine, which is the smallest amino acid. This alternating arrangement is an important feature in the packing of the strands that make up the pleated sheet. 

The X-ray diffraction studies of diketopiperazine, glycine, DL-alanine, and glycylglycine have shown that crystals of these substances consist of discrete molecules and that these molecules are packed together according to definite spatial arrangements which are imposed by the size and shape of the molecules and by the interatomic and intermolecular... 

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