tailieunhanh - Báo cáo khoa học: Quaternary structure and functional properties of Penaeus monodon hemocyanin

The hemocyanin of the tiger shrimp,Penaeus monodon, was investigated with respect to stability and oxygen binding. While hexamers occur as a major component, dodecamers and traces of higher aggregates are also found. Both the hexamers and dodecamers were found to be extremely sta-ble against dissociation at high pH, independently of the presence of cal-cium ions, in contrast to the known crustacean hemocyanins. | iFEBS Journal Quaternary structure and functional properties of Penaeus monodon hemocyanin Mariano Beltramini1 Nadia Colangelo1 Folco Giomi1 Luigi Bubacco1 Paolo Di Muro1 Nadja Hellmann2 Elmar Jaenicke2 and Heinz Decker2 1 Department of Biology University of Padova Padova Italy 2 Institute of Molecular Biophysics Mainz Germany Keywords allosteric interactions hemocyanin oxygen binding Penaeus monodon quaternary structure Correspondence M. Beltramini Department of Biology University of Padova Viale G. Colombo 3 I-35131 Padova Italy Fax 39 049 827 6300 Tel 39 049 827 6337 E-mail beltmar@ Received 25 January 2005 revised 7 February 2005 accepted 28 February 2005 doi The hemocyanin of the tiger shrimp Penaeus monodon was investigated with respect to stability and oxygen binding. While hexamers occur as a major component dodecamers and traces of higher aggregates are also found. Both the hexamers and dodecamers were found to be extremely stable against dissociation at high pH independently of the presence of calcium ions in contrast to the known crustacean hemocyanins. This could be caused by only a few additional noncovalent interactions between amino acids located at the subunit-subunit interfaces. Based on X-ray structures and sequence alignments of related hemocyanins the particular amino acids are identified. At all pH values the p50 and Bohr coefficients of the hexamers are twice as high as those of dodecamers. While the oxygen binding of hexamers from crustaceans can normally be described by a simple two-state model an additional conformational state is needed to describe the oxygen-binding behaviour of Penaeus monodon hemocyanin within the pH range of to . The dodecamers bind oxygen according to the nested Monod-Whyman-Changeaux MWC model as observed for the same aggregation states of other hemocyanins. The oxygen-binding properties of both the hexameric and dodecameric hemocyanins guarantee an efficient .