Heme-binding by Drosophila retinoid- and fatty acid-binding glycoprotein (RFABG), a member of the proapolipophorin gene family.
We previously have cloned and characterized a retinoid- and fatty acid-binding glycoprotein (RFABG) isolated from the heads of Drosophila melanogaster. The protein is composed of two glycosylated subunits (Mr = >200,000 and 70,000) and is a member of the proapolipophorin gene family. Spectral analysis of purified RFABG revealed an absolute absorbance peak at 405 nm, which is typical for a heme-containing protein. The aim of the present study was to characterize the heme-binding properties of RFABG. Upon saturation of the protein solution with carbon monoxide followed by dithionite reduction, a red shift of the Soret peak to 424 nm and the characteristic alpha- and beta- bands at 567 and 539 nm were observed. Native RFABG contains approximately 0.175 moles of heme (mol/mol) indicating that purified RFABG is primarily the apoprotein. Hemin-agarose affinity chromatography of the native RFABG followed by Western blot analysis showed a single immunoreactive band at 70 kDa, indicating that the heme-binding domain resides in the 70 kDa subunit. Although retinoid and fatty acid also bind to the 70 kDa subunit, no competition was observed when an excess of heme was added to a solution of retinoid or fatty acid bound to RFABG. Heme added to a solution of purified RFABG bound in a saturable manner with an affinity of 3.8 x 10(-7) m.Thus, the current study clearly demonstrates that retinoid- and fatty acid-binding glycoprotein is a novel heme-binding protein, which may be involved in the transport and/or metabolism of heme in Drosophila.
Laboratory of Retinal Cell and Molecular Biology, National Eye Institute, National Institutes of Health, Bethesda, MD 20892, USA.
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T
Duncan
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Osawa
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RK
Kutty
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Kutty
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Wiggert
D000818:Animals; D001665:Binding Sites; D015153:Blotting, Western; D002352:Carrier Proteins / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D029721:Drosophila Proteins; D004331:Drosophila melanogaster; D050556:Fatty Acid-Binding Proteins; D006023:Glycoproteins / Q000378:metabolism*; D006418:Heme / Q000378:metabolism*; D008970:Molecular Weight; D011485:Protein Binding
D002352:Carrier Proteins; D029721:Drosophila Proteins; D050556:Fatty Acid-Binding Proteins; D006023:Glycoproteins; C101137:apolpp protein, Drosophila; D006418:Heme