3.0 Types of Secondary Structure
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Loops
Leszczynski & Rose (1986) found a type of loop structure in what was previously classified as "random" conformation. In their survey of 67 proteins, they tabulated 26% Helix, 19% sheet, 26% turns and 21% in loops. These loop structures contain between 6 and 16 residues and are compact and globular in structure. Like turns, they generally contain polar residues and hence are predominantly at the protein surface. Paperclips
Milner-White (1988) has extended the classification of helical C-terminal "caps" (see also Figure 3.1.4.1 ) in his identification of "paperclips". These paperclips occur frequently (in over half the proteins in the presented study), but not exclusively at helix C-termini and can be grouped into two classes based on the number of residues at the loop end. The type shown in Figure 18 A is by far the most common. Glycine occurs very often in position 5 in the paperclip presented in Figure 18 A since a residue at this position must adopt a left-handed helical conformation.
No Title - 31 MAY 96
written by Kurt D. Berndt