PMID:20370823
| Citation |
Nishio, K, Ogasahara, K, Morimoto, Y, Tsukihara, T, Lee, SJ and Yutani, K (2010) Large conformational changes in the Escherichia coli tryptophan synthase beta(2) subunit upon pyridoxal 5'-phosphate binding. FEBS J. 277:2157-70 |
|---|---|
| Abstract |
To understand the basis for the lower activity of the tryptophan synthase beta(2) subunit in comparison to the alpha(2)beta(2) complex, we determined the crystal structures of apo-beta(2) and holo-beta(2) from Escherichia coli at 3.0 and 2.9 A resolutions, respectively. To our knowledge, this is the first report of both beta(2) subunit structures with and without pyridoxal-5'-phosphate. The apo-type molecule retained a dimeric form in solution, as in the case of the holo-beta(2) subunit. The subunit structures of both the apo-beta(2) and the holo-beta(2) forms consisted of two domains, namely the N domain and the C domain. Although there were significant structural differences between the apo- and holo-structures, they could be easily superimposed with a 22 degrees rigid body rotation of the C domain. The pyridoxal-5'-phosphate-bound holo-form had multiple interactions between the two domains and a long loop (residues 260-310), which were missing in the apo-form. Comparison of the structures of holo-Ecbeta(2) and Stbeta(2) in the alpha(2)beta(2) complex from Salmonella typhimurium (Stalpha(2)beta(2)) identified the cause of the lower enzymatic activity of holo-Ecbeta(2) in comparison with Stalpha(2)beta(2). The substrate (indole) gate residues, Tyr279 and Phe280, block entry of the substrate into the beta(2) subunit, although the indole can directly access the active site as a result of a wider cleft between the N and C domains in the holo-Ecbeta(2) subunit. In addition, the structure around betaAsp305 of the holo-Ecbeta(2) subunit was similar to the open state of Stalpha(2)beta(2) with low activity, resulting in lower activity of holo-Ecbeta(2). |
| Links |
PubMed Online version:10.1111/j.1742-4658.2010.07631.x |
| Keywords |
Allosteric Site; Amino Acid Sequence; Apoenzymes/chemistry; Apoenzymes/metabolism; Crystallography, X-Ray; Enzyme Stability; Escherichia coli/enzymology; Holoenzymes/chemistry; Holoenzymes/metabolism; Hydrogen-Ion Concentration; Models, Molecular; Molecular Sequence Data; Protein Multimerization; Protein Structure, Quaternary; Protein Subunits/chemistry; Protein Subunits/metabolism; Pyridoxal Phosphate/chemistry; Pyridoxal Phosphate/metabolism; Salmonella typhimurium/enzymology; Sequence Alignment; Tryptophan Synthase/chemistry; Tryptophan Synthase/metabolism |
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