FIGURE 4.

NADP-binding site of PIG3. A, LIGPLOT (38) describing interactions in the NADP-binding site. Residues Gly-173, Lys-177, and Tyr-192 are interacting with the 2′-phosphate of NADP⁺. B, (A/G)XXSXXG motif in orange, showing Ser-151 hydrogen bonds with the main chain oxygen and nitrogen atoms from the motif residues Ala-148 and Gly-154. C, model of the same region as in B but using the S151V inactive mutant, which apparently presents steric hindrances between Val-151 side chain (gray) and NADP⁺ that may result in the inability of the protein to bind the cofactor.