Lactotransferrin

Abstract: The screening of a bovine submaxillary gland cDNA library yielded 25 clones coding for bovine lactotransferrin. The nucleotide sequence of the longest insert contained a protein-coding region of 2115 nucleotides and a 3′ non-coding region of 194 nucleotides followed by a poly(A) tract of about 55 nucleotides. The predicted peptide sequence included a 16-amino-acid signal sequence upstream of the first amino acid of the native protein. The identity of the clone was confirmed by matching the amino acid sequence predicted from the cDNA with the N-terminal and tryptic peptide sequences derived from purified bovine milk lactotransferrin, and also by similarity with human and murine lactotransferrins. The cDNA described corresponds to a 705-amino-acid-long preprotein that lacks the start methionine. The sequence of the secreted protein is 689 amino acids long and contains five potential glycosylation sites. Bovine lactotransferrin is 69% and 64% identical to human and murine lactotransferrins, respectively.

Abstract: Lactotransferrin (LF) expression was investigated immunocytochemically in postmortem brain tissues of normal controls and patients with Alzheimer's disease (AD). The antibody to LF stained some neurons weakly in young adult brains, but it stained many neurons as well as the glia of all types in elderly brains. LF expression was greatly up-regulated in both neurons and glia in affected AD tissue. It was very strongly associated with such extracellular pathological entities as diffuse and consolidated amyloid deposits and extracellular neurofibrillary tangles. In addition, it was identified in a minority of intracellular neurofibrillary tangles, neuropil threads, and degenerative neurites. LF is an iron scavenger and a complement inhibitor. Up-regulation may be a defense mechanism in AD-affected brain tissue.