The molecular heterogeneity of hemocyanin: Structural and functional properties of the 4x6-meric protein of Upogebia pusilla (Crustacea).
The structural properties of the hemocyanin isolated from the Mediterranean mud shrimp, Upogebia pusilla (Decapoda: Thalassinidea), were investigated. Our intent was to make use of the U. pusilla case to perform a structural comparison between crustacean and chelicerate 4x6-meric hemocyanins. The thalassinidean hemocyanin appears similar in size but different in structural organization compared to the chelicerate 4x6-mer. Ultracentrifuge analyses on the purified protein revealed a sedimentation coefficient of 39S, typical of 4x6 hemocyanins. Electron micrographs are in agreement with a model in which four 2x6-meric building blocks are arranged in a tetrahedron-like quaternary structure and not in the quasi-square-planar orientation characteristic of the chelicerate protein. Size-exclusion chromatography-fast protein chromatography analysis showed elevated instability of the protein in absence of divalent ions or at pH values higher than 8.0. This analysis also shows that the dissociation of the U. pusilla 4x6-meric hemocyanin into hexamers occurs without any intermediate 2x6-meric state, in contrast with the dissociation profile of the chelicerate protein exhibiting several dissociation intermediates. The oxygen-binding properties of U. pusilla hemocyanin were studied to disclose possible effects by the typical allosteric effectors that modulate the functional properties of crustacean hemocyanin. A marked Bohr and lactate effect, but no significant influence of urate, on the oxygen affinity of U. pusilla hemocyanin were found.
Paoli
M
M
Department of Biology, University of Padova, Padova, Italy.
Giomi
F
F
Hellmann
N
N
Jaenicke
E
E
Decker
H
H
Di Muro
P
P
Beltramini
M
M
D000818:Animals; D002850:Chromatography, Gel / Q000379:methods; D033364:Decapoda / Q000737:chemistry* / Q000378:metabolism; D006433:Hemocyanins / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D008854:Microscopy, Electron; D008970:Molecular Weight; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation
D006433:Hemocyanins; D010100:Oxygen