Ernst EG, Behnke WD. Construction and expression of synthetic wild-type and mutant genes encoding porcine pancreatic colipase: tryptophan fluorescence studies.
BIOCHIMICA ET BIOPHYSICA ACTA 1991;
1089:331-8. [PMID:
1859837 DOI:
10.1016/0167-4781(91)90173-j]
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Abstract
Based on the known (95-residue) amino acid (aa) sequence of porcine pancreatic colipase (CLP), a cofactor of pancreatic lipase, a 297 bp gene was designed and assembled from eight synthetic, overlapping DNA fragments. Optimized for expression in bacteria, the CLP-encoding gene (CLP) was inserted into the lacZ gene fragment contained in the small expression vector, pUC8, and cloned in Escherichia coli JM109. Expression of this construct yielded a protein approx. 11 kDa in size, equivalent to CLP, with an Mr of 10,336, plus ten additional amino acids at the N-terminus. The recombinant CLP (reCLP) was solubilized from bacterial inclusion bodies and then purified and refolded. A mutant CLP gene, changing Tyr-55 to Trp, was then constructed by site-directed mutagenesis. Since porcine CLP contains no Trp, this strategy provided a protein with an internal fluorescent probe for biophysical studies. The presence of Trp in the mutant protein was confirmed using fluorescence spectroscopy. Both wild-type (wt) and mutant reCLP reacted on Western blots with an affinity-purified rabbit anti-CLP antibody, raised against native CLP. The Tyr-55 to Trp exchange did not affect the activity of reCLP. Fluorescence studies of the interaction between reCLP and the bile salt, taurodeoxycholate (TDOC), showed that Trp-55 in the hydrophobic binding site of mutant reCLP inserted into the interior of the bile salt micelle.
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