Formation of the alpha 1-microglobulin chromophore in mammalian and insect cells: a novel post-translational mechanism?
alpha 1-Microglobulin is an immunosuppressive plasma protein synthesized by the liver. The isolated protein is yellow-brown, but the hypothetical chromophore has not yet been identified. In this work, it is shown that a human liver cell line, HepG2, grown in a completely synthetic and serum-free medium, secretes alpha 1-microglobulin which is also yellow-brown, suggesting a de novo synthesis of the chromophore by the cells. alpha 1-Microglobulin isolated from the culture medium of insect cells transfected with the gene for rat alpha 1-microglobulin is also yellow-brown, suggesting that the gene carries information about the chromophore. Reduction and alkylation or removal of N- or O-linked carbohydrates by glycosidase treatment did not reduce the colour intensity of the protein. An internal dodecapeptide (amino acid positions 70-81 in human alpha 1-microglobulin) was also yellow-brown. The latter results indicate that the chromophore is linked to the polypeptide. In conclusion, the results suggest that the alpha 1-microglobulin gene carries information activating a post-translational protein modification mechanism which is present in mammalian and insect cells.
Akerström
B
B
Department of Cell and Molecular Biology, Lund University, Sweden.
Bratt
T
T
Enghild
J J
JJ
D000478:Alkylation; D000510:Alpha-Globulins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D006031:Glycosylation; D006801:Humans; D008969:Molecular Sequence Data; D009036:Moths; D010084:Oxidation-Reduction; D010455:Peptides / Q000737:chemistry / Q000302:isolation & purification; D010860:Pigments, Biological / Q000737:chemistry / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D014407:Tumor Cells, Cultured
D000510:Alpha-Globulins; D010455:Peptides; D010860:Pigments, Biological; C016001:alpha-1-microglobulin