Symmetry, stability, and dynamics of multidomain and multicomponent protein systems

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   Figure 1

   Crystal structure of pentameric human serum amyloid P-component (11) showing 5-fold symmetry.

   
   
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   Figure 2

   The structure of the zinc insulin hexamer as defined by Hodgkin and coworkers (14). The hexamer is viewed down the exact 3-fold axis (triangle at the center); the arrows indicate positions of approximate 2-fold axes relating pairs of protomers. Each protomer is represented in a specific color, and the zinc at the center is shown in red.

   
   
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   Figure 3

   Quaternary structures of proteins with the lectin fold. The crystal structures used are pea lectin (32), bovine S-lectin (33), peanut lectin (34), jack bean concanavalin A (35), and human serum amyloid P-component (11). The hexameric Limulus C-reactive protein (Limulus CRP) structure has been generated on the basis of sequence similarity with serum amyloid P-component (36). Symmetry axes are indicated for each structure. Arrows represent 2-fold axes in the plane of the paper.

   
   
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   Figure 4

   Internal symmetry in γ_B-crystallin (45, 46). The two symmetry-related Greek-key motifs within a domain are shown in two different colors and are related by approximate 2-fold axes (arrows). In a similar manner, the two domains are related by an approximate 2-fold axis.

   
   
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   Figure 5

   (a and b) Comparison of monomeric pepsin (a) with two symmetry-related lobes (61) and dimeric HIV proteinase (b) (4) inspired by the analyses of Blundell and coworkers (61–63). The arrows indicate the positions of approximate and perfect 2-fold axes relating domains (pepsin) and protomers (HIV proteinase), respectively. (c) The two topologically equivalent catalytic groups (the “hands” Asp-32 and Asp-215 of pepsin), which have an approximate 2-fold axis shown as an arrow.