Polypeptide globular

Figure 1.1 The amino acid sequence of a protein s polypeptide chain is called Its primary structure. Different regions of the sequence form local regular secondary structures, such as alpha (a) helices or beta (P) strands. The tertiary structure is formed by packing such structural elements into one or several compact globular units called domains. The final protein may contain several polypeptide chains arranged in a quaternary structure. By formation of such tertiary and quaternary structure amino acids far apart In the sequence are brought close together in three dimensions to form a functional region, an active site.

Several motifs usually combine to form compact globular structures, which are called domains. In this book we will use the term tertiary structure as a common term both for the way motifs are arranged into domain structures and for the way a single polypeptide chain folds into one or several domains. In all cases examined so far it has been found that if there is significant amino acid sequence homology in two domains in different proteins, these domains have similar tertiary structures. 

The reverse turn as a polypeptide conformation in globular proteins. Proc. Natl. Acad. Sci. USA 70 538-542, 1973. 

Figure 6.1 A polypeptide chain is extended and flexible in the unfolded, denatured state whereas it is globular and compact in the folded, native state.

Collagen chains are synthesized as longer precursors, called procollagens, with globular extensions—propeptides of about 200 residues—at both ends. These procollagen polypeptide chains are transported into the lumen of the rough endoplasmic reticulum where they undergo hydroxylation and other chemical modifications before they are assembled into triple chain molecules. The terminal propeptides are essential for proper formation of triple... 

When the polypeptide chains of protein molecules bend and fold in order to assume a more compact three-dimensional shape, a tertiary (3°) level of structure is generated (Figure 5.9). It is by virtue of their tertiary structure that proteins adopt a globular shape. A globular conformation gives the lowest surface-to-volume ratio, minimizing interaction of the protein with the surrounding environment. 

Microtubules (MT) are the largest of the cytoskeletal filaments with an outer diameter of about 25 nm, a wall thickness of about 5 nm, and a central lumen measuring about 15 nm. They consist of tubulin and associated proteins. Vertebrate brain tissue is a rich source of extractable tubulin because of the large numbers of microtubules that are present in axons and dendrites. Tubulin obtained from such a natural source is a heterodimer of 100 kD composed of a-tubulin and P-tubulin. Brain a-tubulin is a globular polypeptide that contains 451 amino acid residues, whereas P-tubulin, which is somewhat shorter, is made up of 445 amino acid residues. These two molecular species of tubulin share in common 40% of their amino acid residues. 

Table 5.7 Theoretically predicted polypeptides from the trypsin digestion of S-lacto-globulin (/3LG) . Reprinted from J. Chromatogr., A, 763, Turula, V. E., Bishop, R. T., Ricker, R. D. and de Haseth, J. A., Complete structure elucidation of a globular protein by particle beam liquid chromatography-Fourier transform infrared spectrometry and electrospray liquid chromatography-mass spectrometry - Sequence and conformation of /3-lactoglobulin , 91-103, Copyright (1997), with permission from Elsevier Science...

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