A re-evaluation of the role of type IV antifreeze protein |
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| Affiliation: | 1. Department of Biochemistry, Queen’s University, 18 Staurt Street, Botterell hall, Room 63, Kingston, Ont., Canada K7L 3N6;2. Ocean Sciences Centre, Memorial University of Newfoundland, St. John’s, Nfld, Canada A1C 5S7;1. Department of Companion Animal Medicine and Surgery, Faculty of Veterinary Medicine, Universiti Putra Malaysia, 43400, UPM Serdang, Malaysia;2. Department of Veterinary Preclinical Sciences, Faculty of Veterinary Medicine, University Putra Malaysia, 43400, UPM Serdang, Malaysia;3. Department of Basic Veterinary Sciences, Faculty of Veterinary and Animal Science, Gomal University, D. I. Khan, Pakistan;4. Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400, UPM Serdang, Malaysia;5. Department of Pathology and Microbiology, Faculty of Veterinary Medicine, Universiti Putra Malaysia, 43400, UPM Serdang, Malaysia;6. Department of Surgery and Theriogenology, College of Veterinary Medicine, University of Mosul, Iraq;1. Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen, Denmark;2. Department of Science, Systems and Models, Universitetsvej 1, Roskilde University, DK-4000 Roskilde, Denmark;1. Department of Food Science and Technology, Seoul National University of Science & Technology, Seoul, 01811, Republic of Korea;2. Department of Food and Nutrition, KC University, Seoul, 07661, Republic of Korea;3. Department of Life Science, College of Natural Sciences, Hanyang University, Seoul, 04763, Republic of Korea;4. Department of Biotechnology, College of Biomedical and Health Science, Konkuk University, Chungju, Chungbuk, 27478, Republic of Korea;5. Division of Food Bioscience, College of Biomedical and Health Science, Konkuk University, Chungju, Chungbuk, 27478, Republic of Korea;6. Korean Edible Insect Laboratory, Seoul 04598, Republic of Korea;7. Department of Hotel Food Service and Culinary Arts, Seowon University, Cheongju 28674, Republic of Korea |
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| Abstract: | A lipoprotein-like antifreeze protein (type IV AFP) has previously been isolated only from the blood plasma of the longhorn sculpin. However, the plasma antifreeze activity in all individuals of this species tested from Newfoundland and New Brunswick waters ranges from low to undetectable. A close relative of the longhorn sculpin, the shorthorn sculpin, does have appreciable antifreeze activity in its blood but this is virtually all accounted for by the α-helical, alanine-rich type I AFP, other isoforms of which are also present in the skin of both fishes. We have characterized a putative ortholog of type IV AFP in shorthorn sculpin by cDNA cloning. This 12.2-kDa Gln-rich protein is 87% identical to the longhorn sculpin’s type IV AFP. Recombinant versions of both orthologs were produced in bacteria and shown to have antifreeze activity. Immunoblotting with antibodies raised to type IV AFP shows this protein present in longhorn sculpin plasma at levels of less than 100 μg/mL, which are far too low to protect the blood from freezing at the temperature of icy seawater. This confirms the results of direct antifreeze assays on the plasmas. It appears that type IV AFP has the potential to develop as a functional antifreeze in these fishes but may not have been selected for this role because of the presence of type I AFP. Consistent with this hypothesis is the observation that the type IV AFP gene has not been amplified the way functional antifreeze protein genes have in all other species examined. |
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