RAFT1 (rapamycin and FKBP12 target 1; also called FRAP or mTOR) is a member of the ATM (ataxia telangiectasia mutated)-related family of proteins and functions as the in vivo mediator of the effects ...of the immunosuppressant rapamycin and as an important regulator of messenger RNA translation. In mammalian cells RAFT1 interacted with gephyrin, a widely expressed protein necessary for the clustering of glycine receptors at the cell membrane of neurons. RAFT1 mutants that could not associate with gephyrin failed to signal to downstream molecules, including the p70 ribosomal S6 kinase and the eIF-4E binding protein, 4E-BP1. The interaction with gephyrin ascribes a function to the large amino-terminal region of an ATM-related protein and reveals a role in signal transduction for the clustering protein gephyrin.
We have identified a novel generally expressed homologue of the erythrocyte membrane cytoskeletal protein 4.1, named 4.1G, based on the interaction of its COOH-terminal domain (CTD) with the ...immunophilin FKBP13. The 129-amino acid peptide, designated 4.1G-CTD, is the first known physiologic binding target of FKBP13. FKBP13 is a 13-kD protein originally identified by its high affinity binding to the immunosuppressant drugs FK506 and rapamycin (Jin, Y., M.W. Albers, W.S. Lane, B.E. Bierer, and S.J. Burakoff. 1991. Proc. Natl. Acad. Sci. USA. 88:6677-6681); it is a membrane-associated protein thought to function as an ER chaperone (Bush, K.T., B.A. Henrickson, and S.K. Nigam. 1994. Biochem. J. Tokyo. 303:705-708). We report the specific association of FKBP13 with 4.1G-CTD based on yeast two-hybrid, in vitro binding and coimmunoprecipitation experiments. The histidyl-proline moiety of 4.1G-CTD is required for FKBP13 binding, as indicated by yeast experiments with truncated and mutated 4.1G-CTD constructs. In situ hybridization studies reveal cellular colocalizations for FKBP13 and 4.1G-CTD throughout the body during development, supporting a physiologic role for the interaction. Interestingly, FKBP13 cofractionates with the red blood cell homologue of 4.1 (4.1R) in ghosts, inside-out vesicles, and Triton shell preparations. The identification of FKBP13 in erythrocytes, which lack ER, suggests that FKBP13 may additionally function as a component of membrane cytoskeletal scaffolds.
In this study, we have used the tumor promoter 12-o-tetradecanoylphorbol-13-acetate (TPA), as well as its biologically inactive analogue 4 alpha-phorbol 12,13-didecanoate (4 alpha-PDD), to ...investigate platelet protein phosphorylation and its possible correlation with platelet activation. Our data show that TPA, but not 4 alpha-PDD, induces a preferential phosphorylation of a 30,000 dalton (30 KD) protein. This phosphoprotein is found to be physically associated with an actomyosin-containing platelet cytoskeleton complex. Further analysis using both standard two-dimensional gel electrophoresis and one-dimensional urea-SDS gel electrophoresis reveals that this 30 KD protein has several tropomyosin-like properties. Most importantly, the degree of TPA-induced phosphorylation of the 30 KD protein is directly proportional to the extent of platelet granule release and the shape change of the platelet, as well as to the degree of aggregation. We speculate that this phosphorylated tropomyosinlike protein may play a pivotal role in the regulation of actomyosin-mediated platelet contractility, which has been previously implicated in a variety of platelet functions.
RAPID FINE SAND FILTRATION [with DISCUSSION] Field, Frederick E.; Van Loan, Seth M.; Baylis, John R. ...
Journal - American Water Works Association,
06/1926, Volume:
15, Issue:
6
Journal Article
PDF
