Download MendeleyThe molecular structure of insecticyanin from the tobacco hornworm Manduca sexta L. at 2.6 A resolution.
Holden, H.M., Rypniewski, W.R., Law, J.H., Rayment, I.(1987) EMBO J 6: 1565-1570
- PubMed: 3608987
- DOI: https://doi.org/10.1002/j.1460-2075.1987.tb02401.x
- Primary Citation of Related Structures:
1Z24 - PubMed Abstract:
Insecticyanin, a blue biliprotein isolated from the tobacco hornworm Manduca sexta L., is involved in insect camouflage. Its three-dimensional structure has now been solved to 2.6 A resolution using the techniques of multiple isomorphous replacement, non-crystallographic symmetry averaging about a local 2-fold rotation axis and solvent flattening. All 189 amino acids have been fitted to the electron density map. The map clearly shows that insecticyanin is a tetramer with one of its molecular 2-fold axes coincident to a crystallographic dyad. The individual subunits have overall dimensions of 44 A X 37 A X 40 A and consist primarily of an eight-stranded anti-parallel beta-barrel flanked on one side by a 4.5-turn alpha-helix. Interestingly the overall three-dimensional fold of the insecticyanin subunit shows remarkable similarity to the structural motifs of bovine beta-lactoglobulin and the human serum retinol-binding protein. The electron density attributable to the chromophore is unambiguous and shows that it is indeed the gamma-isomer of biliverdin. The biliverdin lies towards the open end of the beta-barrel with its two propionate side chains pointing towards the solvent and it adopts a rather folded conformation, much like a heme.
