The best-understood mechanisms for generating transport vesicles in the secretory and endocytic pathways involve the localized assembly of cytosolic coat proteins such as clathrin, coat protein complexes COPI and COPII onto membranes.

These coat proteins can deform membranes by themselves, but accessory proteins might help to generate the tight curvature needed to form a vesicle.

Enzymes that pump phospholipid from one leaflet of the bilayer to the other (flippases) can deform membranes by creating an imbalance in the phospholipid number between the two leaflets.

Studies describe a requirement for the yeast Drs2p family of P-type ATPases in both phospholipid translocation and protein transport in the secretory and endocytic pathways. This indicates that flippases work with coat proteins to form vesicles.

References

 Graham TR. Flippases and vesicle-mediated protein transport. Trends Cell Biol. 2004 Dec;14(12):670-7. PMID: #15564043#