Native uridine 5'-diphosphate-sulfoquinovose synthase, SQD1, from spinach purifies as a 250-kDa complex.
Sulfoquinovosyldiacylglycerol is a polar lipid present in photosynthetic membranes. It contributes to the negative surface charge of the membrane and plays a pivotal role under phosphate stress. The SQD1 protein is the key enzyme involved in the formation of the sulfolipid head group precursor, uridine 5(')-diphosphate (UDP)-sulfoquinovose, from UDP-glucose and sulfite. A cDNA encoding the spinach SQD1 protein was isolated and functionally expressed in Escherichia coli. The recombinant enzyme was compared to the native enzyme purified from isolated spinach chloroplasts. While the K(m) for UDP-glucose was indistinguishable for the two forms, the K(m) for sulfite was more than fourfold lower (< microM) for the native enzyme. Sizing by gel filtration indicated that the native form purified as a large complex of approximately 250 kDa, which is more than twice as large as the calculated size for the homodimer. It is proposed that in vivo SQD1 forms a complex with accessory proteins.
Shimojima
Mie
M
Department of Biochemistry and Molecular Biology, Michigan State University, 224 Biochemistry Building, East Lansing 48824-1319, USA.
Benning
Christoph
C
D000595:Amino Acid Sequence; D029681:Arabidopsis Proteins / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D001483:Base Sequence; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D006602:Hexosyltransferases / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010940:Plant Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D018724:Spinacia oleracea / Q000201:enzymology* / Q000235:genetics; D014532:Uridine Diphosphate Glucose / Q000031:analogs & derivatives* / Q000096:biosynthesis*
D029681:Arabidopsis Proteins; D018076:DNA, Complementary; D018744:DNA, Plant; D010940:Plant Proteins; D011994:Recombinant Proteins; C096386:uridine diphosphate sulfoquinovose; D006602:Hexosyltransferases; C456289:SQD2 protein, Arabidopsis; D014532:Uridine Diphosphate Glucose