tailieunhanh - Báo cáo khoa học: Thermal stability of homologous functional units of Helix pomatia hemocyanin does not correlate with carbohydrate content

The thermal stability of the eight functional units ofb-hemocyanin of the gastropodan mollusc Helix pomatiawas investigated by FTIR spectros-copy. Molluscan hemocyanin functional units have a molecular mass of approximately 50 kDa and generally contain three disulfide bridges: two in the mainly a-helical N-terminal domain and one in the C-terminal b-sheet domain. | ỊFEBS Journal Thermal stability of homologous functional units of Helix pomatia hemocyanin does not correlate with carbohydrate content Betul T. Yesilyurt1 Constant Gielens1 and Filip Meersman2 1 Division of Biochemistry Molecular and StructuralBiology Department of Chemistry Katholieke Universiteit Leuven Belgium 2 Division of Molecular and Nanomaterials Department of Chemistry Katholieke Universiteit Leuven Belgium Keywords disulfide bridge FTIR spectroscopy functional unit glycosylation hemocyanin Correspondence F. Meersman Division of Molecular and Nanomaterials Department of Chemistry Katholieke Universiteit Leuven Celestijnenlaan 200F B-3001 Leuven Belgium Fax 32 16 327990 Tel 32 16 327355 E-mail Received 12 February 2008 revised 11 April2008 accepted 15 May 2008 doi The thermal stability of the eight functional units of b-hemocyanin of the gastropodan mollusc Helix pomatia was investigated by FTIR spectroscopy. Molluscan hemocyanin functional units have a molecular mass of approximately 50 kDa and generally contain three disulfide bridges two in the mainly a-helical N-terminal domain and one in the C-terminal b-sheet domain. They show more than 50 sequence homology and it is assumed that they adopt a similar conformation. However the functional units of H. pomatia b-hemocyanin designated HpH-a to HpH-h differ considerably in their carbohydrate content 0-18 wt . Most functional units are exceptionally stable with a melting temperature in the range 77-83 C. Two functional units HpH-b and HpH-c however have a reduced stability with melting temperature values of 73 C and 64 C respectively. Although the most glycosylated functional unit HpH-g has the highest temperature stability there is no linear correlation between the degree of glycosylation of the functional units and the unfolding temperature. This is ascribed to variations in secondary structure as well as in glycan attachment sites. Moreover