FIGURE 5.

Crystal structure of apoNR2B_ATD. A, the strand representation of the crystal structure of apoNR2B_ATD (PDB code 3JPW) (47), which consists of two domains, R1 (light pink) and R2 (light purple) was created with Protein Workshop (60). Arg⁶⁷ (R67; residue highlighted in red with balls and sticks) is situated at the tip of R1 (light pink) and thus is proposed to be exposed to the surrounding aqueous milieu. Left, shown is the front view of the NR2B_ATD crystal structure. Right, shown is a view of the crystal structure when the protein molecule is rotated as denoted. B, several structures that may be critical for the tertiary structure of the ATD upon the removal of Gln²⁹–Arg⁶⁷ are highlighted. The tPA cleavage site Arg⁶⁷ (R67) is highlighted in red; Gly³⁶–Val⁴² fragment (β1 sheet), Val⁶⁸–Met⁷³ (β2 sheet), and Val⁹⁷–Asp¹⁰¹ (β3 sheet) are highlighted in dull yellow; Pro⁷⁸–Asp⁹¹ (α1 helix) and Leu²⁸⁹–His³¹¹ (α8 helix) are highlighted in light green. The hypervariable loop (HVL) is highlighted in dark purple, and the two cysteine residues, Cys⁸⁶ in α1 and Cys³²¹ in HVL (highlighted in orange with balls and sticks), form a disulfide bond that helps to stabilize the ATD structure. The peptide upstream of Val⁶⁸ can dissociate from the receptor after tPA treatment.