FIGURE 4.

Structure of His-GAPDS E. coli GAPDH heterotetramer. a, ribbon diagram of the His-GAPDS-E. coli GAPDH tetramer. The tetramer is formed through the association of a pair of dimers. Chain A (red) and chain C (green) form an E. coli GAPDH dimer, and chain B (yellow, E. coli GAPDH) and chain D (blue, His-GAPDS) form a heterodimer. NAD⁺ is shown in sticks representation. b, chain A, E. coli GAPDH (red) overlaid on chain D, GAPDS (blue). c, C-terminal extension in D subunit. The final refined model for the sequence ³²⁸YMFSREK³³⁴ His-GAPDS is shown in blue bonds representation, with final weighted electron density shown at 1σ. The final refined model for ³²⁷HISK³³⁰ E. coli GAPDH (red) is superimposed. On the right-hand side, the final refined coordinates for the C terminus of E. coli GAPDH, ³²⁷HISK³³⁰, are shown in red bonds representation with final weighted electron density shown at 1σ. d, final refined model for the sequence ¹³⁸NPGSMTV¹⁴⁶ His-GAPDS is shown in blue bonds representation with final weighted electron density shown at 1σ, and the final refined model for the corresponding sequence in E. coli from subunit A, ¹³⁹AGQDI¹⁴³ E. coli GAPDH, is superimposed in red bonds representation. On the right-hand side, the same region ¹³⁹AGQDI¹⁴³ E. coli GAPDH (red) is shown with its own final weighted electron density shown at 1σ. e, trace of tetramer with residue positions that differ in sequence between E. coli GAPDH (A, red; B, yellow; C, green) and GAPDS (blue) shown as blue spheres in the D subunit. Residues that lie at the interfaces between subunits are colored magenta.