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TitleMolecular Engineering of Selective Recognition Elements as Coatings for Sensor Platforms by ...
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Page 73


3.5 Conclusion

Using directed evolutionary screening processes, we identified specific TNT and DNT

binding peptides. Compared with the resulting TNT binding peptide, (Trp-His-Trp-X:

where X represents Gln, Ser, Asn, or Lys), the active site of nature’s known TNT binding

protein Enterobacter cloacae’s pentaerythritol tetranitrate reductase (Trp102, His181,

Tyr186, Thr26) contains many compositional similarities.

PETN-reductase and other

TNT binding proteins display a highly conserved tryptophan residue involved in the

binding event.
102, 103

Furthermore, these previous studies show that changes in the

tryptophan’s neighboring amino acid, histidine, can drastically modulate the TNT binding

ability of these proteins. Similarly, through mutational analysis of our TNT binding

motif (Figure-22b), we have demonstrated the role of multivalent binding involved with

neighboring tryptophan and histidine residues. Various mechanisms exist by which

tryptophan may attribute its strong role in the binding motif for TNT. The PETN-

reductase utilizes the aromatic stacking between tryptophan and the ring structures of


Through computational approaches, researchers have identified similar

dual aromatic residues as part of a high affinity TNT binding motif which parallels the

tryptophan arrangement of our own TNT binding sequence.

Tryptophan’s interaction

with TNT may take on a donor-acceptor character due to the electron deficiency of the

ring in TNT while those of tryptophan are electron rich.

Histidine can also contribute

to π-π interactions.

In addition, imidazole side-chains can coordinate with the nitro

group in the TNT molecules through partial charge-charge interactions or hydrogen

102, 107

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