2HXX image
Entry Detail
PDB ID:
2HXX
Title:
Aminotryptophan Barstar
Biological Source:
Host Organism:
PDB Version:
Deposition Date:
2006-08-04
Release Date:
2006-08-22
Method Details:
Experimental Method:
Resolution:
2.00 Å
R-Value Free:
0.29
R-Value Work:
0.25
R-Value Observed:
0.25
Space Group:
C 1 2 1
Macromolecular Entities
Polymer Type:polypeptide(L)
Description:Barstar
Chain IDs:A, B
Chain Length:89
Number of Molecules:2
Biological Source:Bacillus amyloliquefaciens
Modified Residue
Compound ID Chain ID Parent Comp ID Details 2D Image
4IN A TRP 4-AMINO-L-TRYPTOPHAN
Primary Citation
Aminotryptophan-containing barstar
BIOCHIM.BIOPHYS.ACTA 1764 1147 1158 (2006)
PMID: 16782415 DOI: 10.1016/j.bbapap.2006.04.012

Abstact

The indole ring of the canonical amino acid tryptophan (Trp) possesses distinguished features, such as sterical bulk, hydrophobicity and the nitrogen atom which is capable of acting as a hydrogen bond donor. The introduction of an amino group into the indole moiety of Trp yields the structural analogs 4-aminotryptophan ((4-NH(2))Trp) and 5-aminotryptophan ((5-NH(2))Trp). Their hydrophobicity and spectral properties are substantially different when compared to those of Trp. They resemble the purine bases of DNA and share their capacity for pH-sensitive intramolecular charge transfer. The Trp --> aminotryptophan substitution in proteins during ribosomal translation is expected to result in related protein variants that acquire these features. These expectations have been fulfilled by incorporating (4-NH(2))Trp and (5-NH(2))Trp into barstar, an intracellular inhibitor of the ribonuclease barnase from Bacillus amyloliquefaciens. The crystal structure of (4-NH(2))Trp-barstar is similar to that of the parent protein, whereas its spectral and thermodynamic behavior is found to be remarkably different. The T(m) value of (4-NH(2))Trp- and (5-NH(2))Trp-barstar is lowered by about 20 degrees Celsius, and they exhibit a strongly reduced unfolding cooperativity and substantial loss of free energy in folding. Furthermore, folding kinetic study of (4-NH(2))Trp-barstar revealed that the denatured state is even preferred over native one. The combination of structural and thermodynamic analyses clearly shows how structures of substituted barstar display a typical structure-function tradeoff: the acquirement of unique pH-sensitive charge transfer as a novel function is achieved at the expense of protein stability. These findings provide a new insight into the evolution of the amino acid repertoire of the universal genetic code and highlight possible problems regarding protein engineering and design by using an expanded genetic code.

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Primary Citation of related structures