Investigating Proteins with β-Sheets
► Chapter 7 revealed structural variations that can be observed in proteins built up of α-helices. In this chapter, we will see a similar variability in the structures of proteins composed mostly of β-sheets. One common arrangement of β-strands is called a β-sandwich because two sets of hydrogen-bonded strands pack back to back; the side-chains are the filling of the sandwich. As a classic example, we will examine the immunoglobulin fold and its interaction with an antigen; as an example of a novel β-sandwich fold, we will examine the short N-terminal domain of the vaccinia virus protein A46 whose C-terminus we examined in ► Chap. 7. We will also learn how to investigate whether a protein fold is a novel one. The chapter closes by illuminating another β-fold, known as the jelly roll, frequently found in the particles of icosahedral viruses. Using simple PyMOL commands, the entire shell of an icosahedral virus is assembled. Together, all of the examples show that similar folds involving β-sheets can be constructed by proteins with completely unrelated primary sequences (◘ Table 8.1).
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