X-ray diffraction studies of the structural organisation of prolamellar bodies isolated from Zea mays

Transmission electron microscopy (TEM) indicates that maize prolamellar bodies (PLBs) are built up of tetrapodal units based on a highly convoluted but continuous lipid bilayer exhibiting diamond cubic (Fd3m) symmetry. Such lattices are often described in terms of infinite periodic minimal surfaces (IMPS) exhibiting zero net curvature and dividing the system into two identical subvolumes. If so, X-ray diffraction measurements would be expected to index on a double-diamond (Pn3m) lattice with a unit cell length half that of the TEM lattice. Our measurements index on a Fd3m lattice with a similar repeat distance to the TEM images. The PLB membrane is thus inherently asymmetric, probably as the result of the distribution of membrane protein.