title: A colostrum trypsin inhibitor gene expressed in the Cape fur seal mammary gland during lactation.
abstract: The colostrum trypsin inhibitor (CTI) gene and transcript were cloned from the Cape fur seal mammary gland and CTI identified by in silico analysis of the Pacific walrus and polar bear genomes (Order Carnivora), and in marine and terrestrial mammals of the Orders Cetartiodactyla (yak, whales, camel) and Perissodactyla (white rhinoceros). Unexpectedly, Weddell seal CTI was predicted to be a pseudogene. Cape fur seal CTI was expressed in the mammary gland of a pregnant multiparous seal, but not in a seal in its first pregnancy. While bovine CTI is expressed for 24-48 h postpartum (pp) and secreted in colostrum only, Cape fur seal CTI was detected for at least 2-3 months pp while the mother was suckling its young on-shore. Furthermore, CTI was expressed in the mammary gland of only one of the lactating seals that was foraging at-sea. The expression of β-casein (CSN2) and β-lactoglobulin II (LGB2), but not CTI in the second lactating seal foraging at-sea suggested that CTI may be intermittently expressed during lactation. Cape fur seal and walrus CTI encode putative small, secreted, N-glycosylated proteins with a single Kunitz/bovine pancreatic trypsin inhibitor (BPTI) domain indicative of serine protease inhibition. Mature Cape fur seal CTI shares 92% sequence identity with Pacific walrus CTI, but only 35% identity with BPTI. Structural homology modelling of Cape fur seal CTI and Pacific walrus trypsin based on the model of the second Kunitz domain of human tissue factor pathway inhibitor (TFPI) and porcine trypsin (Protein Data Bank: 1TFX) confirmed that CTI inhibits trypsin in a canonical fashion. Therefore, pinniped CTI may be critical for preventing the proteolytic degradation of immunoglobulins that are passively transferred from mother to young via colostrum and milk.
authors.affiliation: School of BioSciences, The University of Melbourne, Melbourne, VIC 3010, Australia; Cooperative Research Centre for Innovative Dairy Products, Australia. Electronic address: e.pharo@unimelb.edu.au.
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Pharo
authors.affiliation: School of BioSciences, The University of Melbourne, Melbourne, VIC 3010, Australia; Cooperative Research Centre for Innovative Dairy Products, Australia. Electronic address: kylie.cane@gmail.com.
authors.forename: Kylie N
authors.initials: KN
authors.lastname: Cane
authors.affiliation: Biomedicine Discovery Institute, Department of Biochemistry and Molecular Biology, Monash University, Clayton, VIC 3800, Australia. Electronic address: julia.mccoey@gmail.com.
authors.forename: Julia
authors.initials: J
authors.lastname: McCoey
authors.affiliation: Biomedicine Discovery Institute, Department of Biochemistry and Molecular Biology, Monash University, Clayton, VIC 3800, Australia. Electronic address: ashley.buckle@monash.edu.
authors.forename: Ashley M
authors.initials: AM
authors.lastname: Buckle
authors.affiliation: Oceans and Coasts, Department of Environmental Affairs, Private Bag X2, Roggebaai 8012, South Africa. Electronic address: oosthuiz@environment.gov.za.
authors.forename: W H
authors.initials: WH
authors.lastname: Oosthuizen
authors.affiliation: Centre d'Etudes Biologiques de Chizé, CNRS, 79360 Villiers en Bois, France. Electronic address: guinet@cebc.cnrs.fr.
authors.forename: Christophe
authors.initials: C
authors.lastname: Guinet
authors.affiliation: School of BioSciences, The University of Melbourne, Melbourne, VIC 3010, Australia; Cooperative Research Centre for Innovative Dairy Products, Australia; School of Life and Environmental Sciences, Deakin University, Burwood, VIC 3125, Australia. Electronic address: john.arnould@deakin.edu.au.
authors.forename: John P Y
authors.initials: JP
authors.lastname: Arnould
mesh_terms: D000818:Animals; D002417:Cattle; D003126:Colostrum / Q000201:enzymology*; D003198:Computer Simulation; D005260:Female; D046069:Fur Seals / Q000235:genetics* / Q000378:metabolism; D015870:Gene Expression; D007774:Lactation / Q000378:metabolism*; D008322:Mammals / Q000378:metabolism; D008321:Mammary Glands, Animal / Q000378:metabolism*; D011247:Pregnancy; D040681:Structural Homology, Protein; D013552:Swine; D014357:Trypsin / Q000378:metabolism; D014361:Trypsin Inhibitors / Q000737:chemistry / Q000378:metabolism*
chemical_list: D014361:Trypsin Inhibitors; D014357:Trypsin
keywords: BPTI; Kunitz; Milk; Pinniped; Protease; Walrus