Membrane cofactor protein (CD46) of complement. Processing differences related to alternatively spliced cytoplasmic domains.
Membrane cofactor protein (MCP, CD46), a widely distributed regulatory protein, inhibits complement activation on host cells and serves as a measles virus receptor. Most cells express four isoforms (with one of two cytoplasmic tails, CYT-1 or CYT-2). Previously, we noted that MCP precursors had variable intracellular processing. Therefore, we characterized the intracellular transport of individual MCP isoforms. Transfectants were used for pulse-chase analyses. MCP isoforms bearing CYT-1 chased into their mature, surface forms with a half-life (t1/2) of 10-13 min while those with CYT-2 required 35-40 min. The precursor of a tail-less mutant possessed a t1/2 of 160-165 min. Chimeras were constructed that added both tails in opposite orientation onto the isoform (i.e. CYT 1 + 2 or CYT 2 + 1). Chimera 1 + 2 precursor processed with a t1/2 of 35-37 min, similar to CYT-2. Chimera 2 + 1 had a t1/2 of 15-19 min, more closely resembling CYT-1. Thus, in both cases the carboxyl-terminal tail controlled the processing rate. Deletions were made in the beginning, middle, and carboxyl terminus of CYT-1. Deletion of the first or middle six amino acids had no effect on the processing rate. However, deletion of the terminal tetrapeptide (FTSL) slowed the rate to 30-32 min, suggesting that this sequence facilitates exit from the endoplasmic reticulum.
Liszewski
M K
MK
Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri 63110.
Tedja
I
I
Atkinson
J P
JP
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D015703:Antigens, CD / Q000235:genetics / Q000378:metabolism*; D016466:CHO Cells; D003165:Complement System Proteins / Q000235:genetics / Q000378:metabolism*; D006224:Cricetinae; D003593:Cytoplasm / Q000378:metabolism; D016521:Electrophoresis, Gel, Pulsed-Field; D051916:Membrane Cofactor Protein; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D011499:Protein Processing, Post-Translational; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism
D015703:Antigens, CD; D051916:Membrane Cofactor Protein; D008562:Membrane Glycoproteins; D011993:Recombinant Fusion Proteins; D003165:Complement System Proteins