Cloning and expression of glycolipid transfer protein from bovine and porcine brain.

Glycolipid transfer protein (GLTP) is a small (23-24 kDa), basic protein (pI congruent with 9.0) that accelerates the intermembrane transfer of various glycolipids. Here, we report the first cloning of cDNAs that encode the bovine and porcine GLTPs. The cDNA open reading frame for bovine GLTP was constructed by bridge-overlapping extension polymerase chain reaction (PCR) after obtaining partial coding cDNA clones by hot start, seminested, and rapid amplification of cDNA ends-PCR. The cDNA open reading frame for porcine GLTP was constructed by reverse transcriptase-PCR. The encoded amino acid sequences in the full-length bovine and porcine cDNAs were identical, consisting of 209 amino acid residues, and were nearly the same as the published sequence determined by Edman degradation. The cDNA encoded one additional amino acid at the N terminus (methionine), arginine at positions 10 and 200 instead of lysine, and threonine at position 65 instead of alanine. Expression of GLTP-cDNA in Escherichia coli using pGEX-6P-1 vector resulted in glutathione S-transferase (GST)-GLTP fusion protein. Regulation of growth and induction conditions led to approximately 50% of expressed fusion protein being soluble and active. Proteolytic cleavage of GST-GLTP fusion protein (bound to GST-Sepharose) and affinity purification resulted in fully active GLTP. Northern blot analyses of bovine tissues showed a single transcript of approximately 2.2 kilobases and the following hierarchy of mRNA levels: cerebrum > kidney > spleen congruent with lung congruent with cerebellum > liver > heart muscle. Reverse transcriptase-PCR analyses of mRNA levels supported the Northern blot results.