A dimeric form of lipocortin-1 in human placenta

Biochem J. 1989 Oct 1;263(1):97-103. doi: 10.1042/bj2630097.

Abstract

We have characterized a 68 kDa lipocortin from human placenta that was identified as a covalently linked homodimer of lipocortin-1 by peptide mapping and sequence analysis. The site of cross-linking was localized within the 3 kDa N-terminal tail region, an exposed domain that contains the phosphorylation sites for protein tyrosine kinase and protein kinase C and is sensitive to proteolysis. Sequence analysis of the corresponding peptide revealed that glutamine-18 was modified, suggesting that the cross-link may be generated by a transglutaminase. By incubating lipocortin-1 with placental membranes and with labelled glycine ethyl ester we observed a Ca2+-dependent labelling of lipocortin-1 within the tail region, supporting this notion. Like lipocortin-1, the dimer inhibits phospholipase Ad2 activity, is a substrate for the epidermal-growth-factor (EGF) receptor/kinase, and display Ca2+-dependent binding to phosphatidylserine-containing vesicles. In preparations from human placenta the dimer is particularly abundant, accounting for approx. 20% of the lipocortin-1.

MeSH terms

  • Amino Acid Sequence
  • Annexins
  • Blotting, Western
  • Calcium-Binding Proteins / isolation & purification
  • Calcium-Binding Proteins / metabolism*
  • Chromatography, Gel
  • Chromatography, High Pressure Liquid
  • Cross-Linking Reagents
  • Cyanogen Bromide
  • Electrophoresis, Polyacrylamide Gel
  • Female
  • Glycoproteins / isolation & purification
  • Glycoproteins / metabolism
  • Humans
  • Placenta / enzymology
  • Placenta / metabolism*
  • Polymers
  • Pregnancy
  • Protein Conformation

Substances

  • Annexins
  • Calcium-Binding Proteins
  • Cross-Linking Reagents
  • Glycoproteins
  • Polymers
  • Cyanogen Bromide