C. Knupp et al., Partially systematic molecular packing in the hexagonal columnar phase of dogfish egg case collagen, J STRUCT B, 126(2), 1999, pp. 121-130
The collagen that forms the egg case of the dogfish Scyliorhinus canicula i
s stored in bulk in the female nidamental glands. Here the collagen molecul
es are thought to undergo a series of distinct pH-dependent liquid crystall
ine aggregation phase changes before assembling into the final arrangement
encountered in the mature egg case. One liquid crystalline phase is hexagon
al with the centres of two adjacent hexagons about 36 nm apart. We have col
lected tilt series of the hexagonal phase from plastic sections of the nida
mental gland and have produced a three-dimensional reconstruction of the co
llagen arrangement of this phase. The reconstruction features axial columns
of protein density lying regularly on the vertices of hexagonal cells of e
dge length 21 nm. Each column is connected to three nearest neighbours by i
rregular sheets of protein, but there appear to be preferred molecular dire
ctions at about 40 degrees to 50 degrees to the columns. The reconstruction
has been interpreted in terms of known interactions of this collagen in ot
her assemblies. (C) 1999 Academic Press.