| Summary: | <p>Abstract</p> <p>Background</p> <p>Inactive protein inclusion bodies occur commonly in <it>Escherichia coli </it>(<it>E. coli</it>) cells expressing heterologous proteins. Previously several independent groups have found that active protein aggregates or pseudo inclusion bodies can be induced by a fusion partner such as a cellulose binding domain from <it>Clostridium cellulovorans </it>(CBDclos) when expressed in <it>E. coli</it>. More recently we further showed that a short amphipathic helical octadecapeptide 18A (EWLKAFYEKVLEKLKELF) and a short beta structure peptide ELK16 (LELELKLKLELELKLK) have a similar property.</p> <p>Results</p> <p>In this work, we explored a third type of peptides, surfactant-like peptides, for performing such a "pulling-down" function. One or more of three such peptides (L<sub>6</sub>KD, L<sub>6</sub>K<sub>2</sub>, DKL<sub>6</sub>) were fused to the carboxyl termini of model proteins including <it>Aspergillus fumigatus </it>amadoriase II (AMA, all three peptides were used), <it>Bacillus subtilis </it>lipase A (LipA, only L<sub>6</sub>KD was used, hereinafter the same), <it>Bacillus pumilus </it>xylosidase (XynB), and green fluorescent protein (GFP), and expressed in <it>E. coli</it>. All fusions were found to predominantly accumulate in the insoluble fractions, with specific activities ranging from 25% to 92% of the native counterparts. Transmission electron microscopic (TEM) and confocal fluorescence microscopic analyses confirmed the formation of protein aggregates in the cell. Furthermore, binding assays with amyloid-specific dyes (thioflavin T and Cong red) to the AMA-L<sub>6</sub>KD aggregate and the TEM analysis of the aggregate following digestion with protease K suggested that the AMA-L<sub>6</sub>KD aggregate may contain structures reminiscent of amyloids, including a fibril-like structure core.</p> <p>Conclusions</p> <p>This study shows that the surfactant-like peptides L<sub>6</sub>KD and it derivatives can act as a pull-down handler for converting soluble proteins into active aggregates, much like 18A and ELK16. These peptide-mediated protein aggregations might have important implications for protein aggregation <it>in vivo</it>, and can be explored for production of functional biopolymers with detergent or other interfacial activities.</p>
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