Sheet Motifs

The DNA-binding motifs discussed in this and the preceding two chapters are those most frequently found in procaryotes and eucaryotes. However, other motifs are known, for example the p sheet motif of the met repressor in Escherichia coli which binds to the major groove of DNA. No doubt others remain to be discovered. 

Approximately 500 of the 820 amino acid residues of the myosin head are highly conserved between various species. One conserved region, located approximately at residues 170 to 214, constitutes part of the ATP-binding site. Whereas many ATP-binding proteins and enzymes employ a /3-sheet-a-helix-/3-sheet motif, this region of myosin forms a related a-f3-a structure, beginning with an Arg at (approximately) residue 192. The /3-sheet in this region of all myosins includes the amino acid sequence... 

The structural adaptation exhibited by GS bilayer frameworks is achieved through a variety of mechanisms associated with the intrinsic conformational softness of the host framework, including (1) formation of a shifted-ribbon GS sheet motif (Figure 4h) in which adjacent ribbons are shifted from the quasihexagonal arrangement, by as much as ai/2, such that they are connected by one strong (G)N-H—O(S)... 

Chart 10.1 Four biomimetic modules used in our design of modular polymers (a) strong quadmple H bonding motif to form loops, (b) strong quadmple H bonding motif to form double-closed loop (DCL) modules, (c) peptidomimetic 8-sheet motifs to form DCL modules, and (d) small mechanically stable proteins as domains. 

DNA binding of Smad proteins takes place via a DNA binding motif, which differs substantially from classical DNA binding motives. The DNA binding domain of the Smad proteins contains a P-sheet motif, which positions itself in the large groove of the DNA (Shi et al 1998). 

Some Regulatory Proteins Use the /3-Sheet Motif Involvement of Small Molecules in Regulatory Protein Interaction... 

Despite the dominance of the a-helical motif as a recognition unit, the /3-sheet motif has been used in a limited number of cases. In these cases (three are known) two chains in the anti-parallel orientation interact with half-sites in adjacent large grooves of the DNA (see fig. 30.28 for an example). (The /3-sheet motif obviously works in these cases de-... 

Ujah EC (1992) Study of beta-sheet motifs at different levels of structural abstradion using... 

Assuming the pleated sheet-like motif and the ribbon-like motif as reference H-bonded core structures, a further increase in the steric demand of the residues, as for example the presence of aromatic rings as substituents on the diol or diamine moiety, or the absence of the required trans configuration, lead to a loss of efficiency in the recognition process with formation of incomplete ribbon-like or staircase-like structures. In the latter cases, competition experiments show that matched complexes with the pleated sheet-motif or with the ribbon-like motif of the core crystallize more easily than those characterized by incomplete or low organized core structures. Thus, when the complex 29 38 was melted with 1 equiv. of (i ,i )-tra x-l,2-cyclohexanediol (31) and the mixture was crystallized from benzene, again 29 31 was obtained as the only crystalline product (Scheme 22) [60]. 

Figure 22 Sheet motifs (a) the up-and-down barrel (b) the Greek key barrel (c) the jelly-roll barrel and (d) the structure in pectate lyase [119]...

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