Difference between the P4 and P5 subtypes of P-type ATPases in plants
There are numerous differences between the various subtypes of P-type ATPases, simply because they have different amino acid sequences. Three important differences between P4 and P5 subtypes of P-type ATPases are the following:


Structurally, P4 ATPases have their supporting structural domain (S) in the C-terminus, while P5 ATPases have the S domain divided over the N and C termini. Figure 1 shows the basic structure of P-type ATPases.
Structurally, P4-ATPAses require a beta-subunit for proper function (Poulsen et al., 2008). As the substrate for P5-ATPases is unknown, it could not yet be tested if they also require a beta-subunit.
Functionally, P4-ATPases are putative lipid flippases, while P5-ATPase pumps have so far (per the 2011 report cited) no assigned substrate specificity.



Schematic outline of P-type ATPases. Source: Palmgren &amp; Poul Nissen (2011)

References
- Palmgren &amp; Poul Nissen, Annu Rev Biophys (2011); 40: 243–66
- Poulsen et al., Plant Cell (2008); 20: 658–76