FIGURE 7.

Cooperation between the P + 4 position in TM4 and residues in TM1–3 for PS selection. A, the Dnf1 residues highlighted in purple can be mutated to residues that allow PS transport. Mutations in the highlighted TM1 and 2 positions to Atp8a1 residues can rescue function of a Drs2 or Dnf1 P + 4 leucine mutant. B–D, Ca²⁺ ATPase crystal structure in the E2 conformation with a PE molecule cocrystallized. The equivalent residues contributing to phospholipid specificity in Dnf1 and Drs2 have been color-coded for reference: cyan, Asp-254 (equivalent to Dnf1 Asn-550, Drs2 Asn-445); red, Pro-312 (Dnf1 Tyr-618, Drs2 Phe-511); pink, Ile-315 (Dnf1 Val-621, Drs2 Val-514); orange, Thr-316 (Dnf1 Glu-622, Drs2 Glu-515); blue, Asn-101 (Dnf1 Thr-254, Drs2 Ser-261); and yellow, Gly-105 (Dnf1 Asp-258, Drs2 Glu-265) (PDB code 2AGV (46).