Structure of the month - September 2013

Table 1.

Figure 1.

Crystal structure of the covalent reaction intermediate formed between the thiamin cofactor and substrate D-xylulose-5-phosphate (X5P) at the active site of human transketolase showing the final refined model of the intermediate with corresponding 2mFoDFc electron density map (blue, contoured at 3.5σ) in stereo view. The carbons of the substrate X5P are labeled.

Figure 2. 

Close-up of the intermediate highlighting the out-of-plane distortion of the C2-C2x bond relative to ring plane of the aromatic thiazolium nucleus of thiamin shown in grey. Bond-lengths of carbon-carbon bonds (in Å) are indicated including the estimated standard deviations in parentheses obtained by full-matrix refinement using SHELX-2012. The scissile C2x-C3x bond of the substrate is highlighted. Note the elongated C2x-C3x bond of the substrate (bond length shown in red) compared to non-scissile bonds of the substrate, which implicates a reduced bond dissociation barrier.