We made fusions between Escherichia coil maltose-binding protein (MBP) and the mammalian aspartic proteinases pepsinogen or procathepsin D. When MBP was at the N-terminus, the fusions were soluble in E. coil. When the order was reversed, the chimeric proteins formed inclusion bodies. The data suggest that the solubility of fusion proteins is controlled by whether the protein domains emerging first from the ribosome normally fold into soluble or insoluble states. The soluble MBP-aspartic proteinase fusions were stable but proteolytically inactive. MBP-pepsinogen, however, was efficiently renatured from 8 M urea in vitro, suggesting that the E. coli cytoplasm does not support folding of the mammalian partner protein to the native state. Thus, inclusion body formation may be the consequence, rather than the cause, of non-native folding in vivo and in E. coil soluble proteins may fold into states different from those reached in vitro.
|Original language||English (US)|
|Number of pages||5|
|Journal||Biochemical and Biophysical Research Communications|
|State||Published - Mar 27 1998|
Bibliographical noteFunding Information:
The authors thank Drs. P. M. Horowitz and G. R. Mundy for reading the manuscript. This research was supported by Merit and Associate Career Research Scientist awards from the Veterans' Administration Research Service to J.M.C. and by NIH P01 CA 40035 to G.R.M.