Characterization of the third member of the MCAT family of cationic amino acid transporters. Identification of a domain that determines the transport properties of the MCAT proteins.
We have identified the third member of a family of cationic amino acid transporters in lipopolysaccharide-stimulated murine macrophages. The deduced amino acid sequence of this transporter is the same as MCAT-2 (mouse cationic amino acid transporter-2), the low affinity transporter expressed in hepatocytes, except for a stretch of 41 amino acids that connects the eighth and ninth membrane-spanning domains. These transporters apparently result from differential splicing of transcripts from a single gene and therefore have been named MCAT-2A (hepatocyte) and MCAT-2B (macrophage). Despite their similarity, MCAT-2B is saturated at one-fifth the arginine concentration, has a lower apparent Vmax, and is more sensitive to trans-stimulation than MCAT-2. Introduction of the unique regions of MCAT-2A and MCAT-2B into the equivalent portion of the related protein, MCAT-1, created chimeric transporters with properties most like the donor of this region. Our findings suggest these 41 amino acids contain a domain that binds the amino acid substrate during its translocation across the membrane.
Closs
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EI
Howard Hughes Medical Institute, Brigham and Women's Hospital, Boston, Massachusetts 02115.
Lyons
C R
CR
Kelly
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Cunningham
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JM
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001692:Biological Transport; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D002412:Cations; D002478:Cells, Cultured; D018076:DNA, Complementary; D008099:Liver / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism; D008562:Membrane Glycoproteins; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D011991:Receptors, Virus; D017386:Sequence Homology, Amino Acid; D014982:Xenopus laevis
D002352:Carrier Proteins; D002412:Cations; D018076:DNA, Complementary; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D011991:Receptors, Virus; C070506:ecotropic murine leukemia virus receptor