title: Elevated extrahepatic expression and secretion of mammary-associated serum amyloid A 3 (M-SAA3) into colostrum.
abstract: Mammary-associated serum amyloid A 3 (M-SAA3) was secreted at highly elevated levels in bovine, equine and ovine colostrum and found at lower levels in milk 4 days postparturition. N-terminal sequencing of the mature M-SAA3 protein from all the three species revealed a conserved four amino acid motif (TFLK) within the first eight residues. This motif has not been reported to be present in any of the hepatically-produced acute phase SAA (A-SAA) isoforms. Cloning of the bovine M-Saa3 cDNA from mammary gland epithelial cells revealed an open reading frame that encoded a precursor protein of 131 amino acids which included an 18 amino acid signal peptide. The predicted 113 residue mature M-SAA3 protein had a theoretical molecular mass of 12,826Da that corresponded with the observed 12.8kDa molecular mass obtained for M-SAA3 in immunoblot analysis. The high abundance of this extrahepatically produced SAA3 isoform in the colostrum of healthy animals suggests that M-SAA3 may play an important functional role associated with newborn adaptation to extrauterine life and possibly mammary tissue remodeling.
authors.affiliation: Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, NE 68198, USA. tmcdonal@unmc.edu
authors.forename: T L
authors.initials: TL
authors.lastname: McDonald
authors.forename: M A
authors.initials: MA
authors.lastname: Larson
authors.forename: D R
authors.initials: DR
authors.lastname: Mack
authors.forename: A
authors.initials: A
authors.lastname: Weber
mesh_terms: D020816:Amino Acid Motifs / Q000276:immunology; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002417:Cattle; D002846:Chromatography, Affinity / Q000662:veterinary; D003126:Colostrum / Q000737:chemistry* / Q000276:immunology; D004247:DNA / Q000737:chemistry; D004591:Electrophoresis, Polyacrylamide Gel / Q000662:veterinary; D004797:Enzyme-Linked Immunosorbent Assay / Q000662:veterinary; D006736:Horses; D008321:Mammary Glands, Animal / Q000378:metabolism; D008892:Milk / Q000737:chemistry / Q000276:immunology; D008969:Molecular Sequence Data; D008970:Molecular Weight; D020033:Protein Isoforms; D012313:RNA / Q000737:chemistry / Q000302:isolation & purification; D011817:Rabbits; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000662:veterinary; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D000685:Serum Amyloid A Protein / Q000096:biosynthesis* / Q000302:isolation & purification / Q000378:metabolism; D012756:Sheep
chemical_list: D020033:Protein Isoforms; D000685:Serum Amyloid A Protein; D012313:RNA; D004247:DNA