| The mRNA sequence for bovine lactoferrin, a bacteriostatic iron binding glycoprotein expressed in the secretory epithelia of the mammary gland, was determined by sequencing three over-lapping cDNA clones and direct sequencing of the mRNA. The nucleic acid sequence of the coding region shows homologies relative to murine lactoferrin, human transferrin, porcine transferrin and hen ovotransferrin of 67%, 67% 65%, and 61% respectively.; The mRNA codes for a 708 amino acid protein which includes a 19 amino acid signal peptide immediately preceding a sequence identical to the N-terminal 40 amino acids of the mature protein previously sequenced by Rejman et al. (1989). Sequence homologies of related proteins relative to the deduced amino acid sequence of bovine lactoferrin are notable (human lactoferrin (70%), murine lactoferrin (64%), human transferrin (60%), porcine transferrin (61%), and hen ovotransferrin (53%)). Five potential glycosylation sites (Asn-X-Ser/Thr) were identified while four glycans have been reported on bovine lactoferrin by Spik et al. (1988). Amino acid residues involved in iron binding in human lactoferrin (Anderson et al., 1989) and cysteines involved in disulfide bonds (Metz-Boutigue et al., 1984) are matched in identity and relative position in bovine lactoferrin. Predictions of protein secondary structure by Garnier-Osguthorpe-Robson analysis for bovine lactoferrin were very similar to predictions for human lactoferrin. Bovine lactoferrin mRNA concentrations from an involuting mammary gland (three days after last milking) were significantly higher than concentrations in developing (two days before parturition) and lactating glands. The pattern of mRNA concentrations is similar to patterns of protein secretion. |
