Molecular heterogeneity and alternative splicing of human lactoperoxidase.
Human lactoperoxidase (LPO) exists as two distinct molecules independent of glycosylation. The N-terminus of one form is blocked and has not been identified while the other is proteolytically processed at the N-terminus similar to myeloperoxidase. Our analysis identified alternatively spliced human LPO mRNAs that may explain the observed molecular heterogeneity of LPO. Two mRNAs omit propeptide encoding exons while retaining the 5' exon encoding the secretion signal, consistent with the heterogeneity and suggesting a possible functional role for the propeptide. Two LPO forms were expressed using baculovirus and both showed similar enzyme activity. LC/MS/MS analysis of trypsin digested, partially purified, salivary LPO confirmed the larger unprocessed LPO is present in saliva. To compare variant expression patterns, antisera were raised against purified recombinant (rhLPO) as well as against an antigenic peptide sequence within the exons encoding the propeptide region. Immunohistochemistry demonstrated proLPO was differently localized within gland cells compared to other forms of LPO. The data suggested splice variants may contribute to LPO molecular heterogeneity and its regulation by intracellular compartmental localization.
Fragoso
Miryam A
MA
Department of Cell Biology and Anatomy, Miller School of Medicine, University of Miami, 1600 NW 10th Avenue, Miami, FL 33136, USA.
Torbati
Aliza
A
Fregien
Nevis
N
Conner
Gregory E
GE
D017398:Alternative Splicing; D002478:Cells, Cultured; D003001:Cloning, Molecular; D005091:Exons; D014644:Genetic Variation; D006801:Humans; D007438:Introns; D007784:Lactoperoxidase / Q000737:chemistry* / Q000235:genetics*; D008168:Lung / Q000201:enzymology; D012333:RNA, Messenger / Q000235:genetics; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D020545:Respiratory Mucosa / Q000166:cytology / Q000201:enzymology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014132:Trachea / Q000201:enzymology
D012333:RNA, Messenger; D011994:Recombinant Proteins; D007784:Lactoperoxidase