Since Phosphatidylcholine (PC) and phosphatidylserine (PS) are roughly cylindrical in shape , they tend to form flat bilayers. Phosphatidylethanolamine (PE) on the other hand is conical in shape which bends the lipid bilayer when present asymmetrically along with PC and PS. What kind of structure will form when PE is present exclusively?
PCs are lipids with large head groups, so are more of a cylindrical shape, as a result, they tend to form flat bilayers.
PE is a lipid with a small head group, so is in a conical shape. However, they are generally present as inverted cones, providing maximum curvature to the membranes.
So, PEs are generally found in highly curved membranes , for eg:- viral budding, microvilli, micelle, internal vesicles formed for transportation, Inner mitochondrial membrane, Gram-negative bacterial membranes.
You can check out this article, where researchers performed lipid content profiling for E.coli. (https://www.sciencedirect.com/science/article/pii/S0014579315006912)
You can also check out this research article for lipid profiling of rat intestinal microvilli.(https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1186751/pdf/biochemj00720-0057.pdf)