|Haemoglobin structure and biochemical characteristics of the sulphide-binding component from the deep-sea clam Calyptogena magnifica|
Zal, F.; Leize, E.; Oros, D.R.; Hourdez, S.; Van Dorsselaer, A.; Childress, J.J. (2000). Haemoglobin structure and biochemical characteristics of the sulphide-binding component from the deep-sea clam Calyptogena magnifica. Cah. Biol. Mar. 41(4): 413-423
In: Cahiers de Biologie Marine. Station Biologique de Roscoff: Paris. ISSN 0007-9723, more
|Authors|| || Top |
- Zal, F.
- Leize, E.
- Oros, D.R.
- Hourdez, S.
- Van Dorsselaer, A.
- Childress, J.J.
Calyptogena magnifica is a large heterodont clam belonging to the family vesicomyidae that lives at a depth of ca. 2600 m, near deep-sea hydrothermal vent areas on the East-Pacific Rise and Galapagos Rift. This species harbors abundant autotrophic sulphide-oxidizing bacteria contained in bacteriocytes and located in the gills. Unlike the tube worm Riftia pachyptila, which possesses extracellular haemoglobins that bind sulphide and oxygen simultaneously and reversibly at two different sites, Calyptogena magnifica possesses in its haemolymph two different types of molecules for these functions: an intracellular circulating haemoglobin (Hb) for oxygen binding and a sulphide-binding component (SBC) dissolved in the serum. To elucidate its quaternary structure, the haemoglobin was purified by gel chromatography (FPLC) and then analysed by electrospray ionization mass spectrometry (ESI-MS). FPLC analysis revealed a molecular mass of approximately 68 kDa. By mass spectrometry, under native condition, we found that this molecule contains two subunits of molecular masses 16134.0 Da (alpha ) and 32513.1 Da (beta gamma). After reduction, the beta gamma ubunit corresponds to a covalent heterodimer consisting of chains beta and gamma with Mr of 16148.0_and 16371.0, respectively. Our data suggest that C. magnifica intracellular Hb is a tetrameric molecule with three possible associations: (beta gamma) 2, (beta gamma) (alpha)2), and/or (alpha)4. The electron micrographs show that the sulphide-binding serum component is a dumbbell-shaped molecule consisting of two globular subunits of 74 plus or minus 5 nm. It is a glycosylated molecule (non-haeme) that also possesses a protein moiety. Its absorbance peak shifts from 280 nm to 208 nm when it binds sulphide. This molecule moreover possesses unusual solubility properties suggesting that it may be a lipoprotein. It has a high zinc content and there is a 1:1 ratio between zinc and sulphide bound suggesting that zinc is the sulphide-binding site of this compound.