Molecular characterization of Golgin-245, a novel Golgi complex protein containing a granin signature

Abstract

The serum from a Sjogren's syndrome patient with anti-Golgi antibodies was used as a probe to isolate a 4.6-kilobase pair cDNA insert from a HeLa cDNA library. Expression of the cDNA in Escherichia coli and the in vitro translation products of the cDNA yielded a recombinant protein that migrated in SDS-polyacrylamide gel electrophoresis at 180 kDa. This protein was immunoprecipitated by the human anti-Golgi serum and by immune rabbit serum but not by normal human serum or preimmune rabbit serum. Western blot analysis showed that the prototype human and immune rabbit sera recognized a 245-kDa protein, suggesting that the isolated clone contained a partial cDNA. The 5'-upstream sequence obtained by the rapid amplification of cDNA ends methodology using human placental cDNA and the combined HeLa cDNA contained 6965 base pairs and encoded a protein of 245 kDa and, like other Golgi autoantigens described earlier, is highly rich in coiled-coils. The deduced amino acid sequence included the decapeptide ESLALEELEL, which was identified as one of two signature sequences previously reported in a family of peptide hormones and neuropeptides known as 'granins.' This is the first report of a Golgi complex autoantigen that bears structural similarities to the granin family of proteins.