TIP47 is not a component of lipid droplets.
TIP47 functions in the delivery of mannose 6-phosphate receptors from endosomes to the trans-Golgi network both in vitro and in vivo. It binds directly and very specifically to the cytoplasmic domains of both the cation-independent and cation-dependent mannose 6-phosphate receptors. TIP47 is 43% identical to a lipid droplet-associated protein named adipophilin; much of the identity resides near the N termini of these proteins. It was recently reported in this journal, in a study using antiserum from this laboratory, that TIP47 is a constituent of lipid droplets (Wolins, N. E., Rubin, B., and Brasaemle, D. L. (2001) J. Biol. Chem. 276, 5101-5108). We show here that the findings of Wolins et al. were likely due to either a cross-reactive, unidentified protein in HeLa cells that is recognized by our antiserum and/or the fact that our serum also cross-reacts with the adipophilin protein itself, shown directly by expression of adipophilin in Escherichia coli. Using antibodies specific for residues 152-434 of TIP47, we show that TIP47 is not a constituent of lipid droplets.
Barbero
P
P
Department of Biochemistry, Stanford University School of Medicine, Stanford, California 95307, USA.
Buell
E
E
Zulley
S
S
Pfeffer
S R
SR
D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies / Q000276:immunology; D020126:Brefeldin A / Q000494:pharmacology; D002460:Cell Line; D003429:Cross Reactions; D004268:DNA-Binding Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008563:Membrane Lipids / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000276:immunology; D008969:Molecular Sequence Data; D019301:Oleic Acid / Q000494:pharmacology; D000070780:Perilipin-2; D000070796:Perilipin-3; D011257:Pregnancy Proteins; D017527:Receptor, IGF Type 2 / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D033921:Vesicular Transport Proteins
D000906:Antibodies; D004268:DNA-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008563:Membrane Lipids; D008565:Membrane Proteins; C000602982:PLIN2 protein, human; C038196:PLIN3 protein, human; D000070780:Perilipin-2; D000070796:Perilipin-3; D011257:Pregnancy Proteins; D017527:Receptor, IGF Type 2; D033921:Vesicular Transport Proteins; D020126:Brefeldin A; D019301:Oleic Acid