TAILIEUCHUNG - Báo cáo khoa học: Fully active QAE isoform confers thermal hysteresis activity on a defective SP isoform of type III antifreeze protein

Type III antifreeze protein is naturally expressed as a mixture of sulfopro-pyl-Sephadex (SP) and quaternary aminoethyl-Sephadex (QAE)-binding isoforms, whose sequence identity is approximately 55%. We studied the ice-binding properties of a SP isoform (nfeAFP6) and the differences from those of a QAE isoform (nfeAFP8); both of these isoforms have been identified from the Japanese fish Zoarces elongatus Kner. | Fully active QAE isoform confers thermal hysteresis activity on a defective SP isoform of type III antifreeze protein Manabu Takamichi1 2 Yoshiyuki Nishimiya1 Ai Miura1 and Sakae Tsuda1 2 1 FunctionalProtein Research Group Research Institute of Genome-based Biofactory National institute of Advanced Industrial science and Technology AIST Sapporo Japan 2 Division of BiologicalSciences Graduate Schoolof Science Hokkaido University Sapporo Japan Keywords cooperative effect ice growth inhibition notched-fin eelpout thermal hysteresis type III antifreeze protein Correspondence S. Tsuda FunctionalProtein Research Group Research Institute of Genome-based Biofactory NationalInstitute of Advanced IndustrialScience and Technology AIST 2-17-2-1 Tsukisamu-Higashi Sapporo 062-8517 Japan Fax 81 11 857 8983 Tel 81 11 857 8983 E-mail Received 15 November 2008 revised 29 December 2008 accepted 5 January 2009 doi Type III antifreeze protein is naturally expressed as a mixture of sulfopro-pyl-Sephadex SP and quaternary aminoethyl-Sephadex QAE -binding isoforms whose sequence identity is approximately 55 . We studied the ice-binding properties of a SP isoform nfeAFP6 and the differences from those of a QAE isoform nfeAFP8 both of these isoforms have been identified from the Japanese fish Zoarces elongatus Kner. The two isoforms possessed ice-shaping ability such as the creation of an ice bipyramid but nfeAFP6 was unable to halt crystal growth and exhibited no thermal hysteresis activity. For example the ice growth rate for nfeAFP6 was 1000-fold higher than that for nfeAFP8 when measured for mM protein solution at C below the melting point. Nevertheless nfeAFP6 exhibited full thermal hysteresis activity in the presence of only 1 nfeAFP8 . nfeAFP8 nfeAFP6 the effectiveness of which was indistinguishable from that of nfeAFP8 alone. We also observed a burst of ice crystal growth from the tip of the ice bipyramid for both

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