Interacting proteins dictate function of the minimal START domain phosphatidylcholine transfer protein/StarD2.
The Star (steroidogenic acute regulatory protein)-related transfer (START) domain superfamily is characterized by a distinctive lipid-binding motif. START domains typically reside in multidomain proteins, suggesting their function as lipid sensors that trigger biological activities. Phosphatidylcholine transfer protein (PC-TP, also known as StarD2) is an example of a START domain minimal protein that consists only of the lipid-binding motif. PC-TP, which binds phosphatidylcholine exclusively, is expressed during embryonic development and in several tissues of the adult mouse, including liver. Although it catalyzes the intermembrane exchange of phosphatidylcholines in vitro, this activity does not appear to explain the various metabolic alterations observed in mice lacking PC-TP. Here we demonstrate that PC-TP function may be mediated via interacting proteins. Yeast two-hybrid screening using libraries prepared from mouse liver and embryo identified Them2 (thioesterase superfamily member 2) and the homeodomain transcription factor Pax3 (paired box gene 3), respectively, as PC-TP-interacting proteins. These were notable because the START domain superfamily contains multidomain proteins in which the START domain coexists with thioesterase domains in mammals and with homeodomain transcription factors in plants. Interactions were verified in pulldown assays, and colocalization with PC-TP was confirmed within tissues and intracellularly. The acyl-CoA thioesterase activity of purified recombinant Them2 was markedly enhanced by recombinant PC-TP. In tissue culture, PC-TP coactivated the transcriptional activity of Pax3. These findings suggest that PC-TP functions as a phosphatidylcholine-sensing molecule that engages in diverse regulatory activities that depend upon the cellular expression of distinct interacting proteins.
Kanno
Keishi
K
Department of Medicine, Division of Gastroenterology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.
Wu
Michele K
MK
Agate
Diana S
DS
Fanelli
Brandon J
BJ
Wagle
Neil
N
Scapa
Erez F
EF
Ukomadu
Chinweike
C
Cohen
David E
DE
D020816:Amino Acid Motifs / Q000502:physiology; D000818:Animals; D002460:Cell Line; D018507:Gene Expression Regulation, Developmental / Q000502:physiology; D006801:Humans; D008099:Liver / Q000166:cytology / Q000196:embryology*; D051379:Mice; D018345:Mice, Knockout; D009928:Organ Specificity / Q000502:physiology; D000072041:PAX3 Transcription Factor; D051761:Paired Box Transcription Factors / Q000235:genetics / Q000378:metabolism*; D010713:Phosphatidylcholines / Q000235:genetics / Q000378:metabolism; D049294:Phospholipid Transfer Proteins / Q000235:genetics / Q000378:metabolism*; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary / Q000502:physiology; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity / Q000502:physiology; D013869:Thiolester Hydrolases / Q000235:genetics / Q000378:metabolism*; D020798:Two-Hybrid System Techniques; D000098682:Steroidogenic Acute Regulatory Protein
D000072041:PAX3 Transcription Factor; C489409:PAX3 protein, human; D051761:Paired Box Transcription Factors; D010713:Phosphatidylcholines; D049294:Phospholipid Transfer Proteins; D010750:Phosphoproteins; D011994:Recombinant Proteins; D000098682:Steroidogenic Acute Regulatory Protein; C068686:Pax3 protein, mouse; C514740:ACOT13 protein, human; D013869:Thiolester Hydrolases