Expression of Oligomeric Amiloride-Sensitive Epithelial Sodium Channel in Sf9 Insect Cells

Abstract

Elucidation of the structure and function of proteins isolated from cell lines or tissue source is limited by their lower abundance. Thus, it is a common practice to utilize a heterologous expression systems such as Escherichia coli (E. coli), yeast, mammalian, and Sf9 cells for the large-scale production of the protein so as to carry out detailed structure-function relations on the expressed protein (1–4). In most cases, the expressed recombinant proteins are monomeric and function independently without association with other proteins. However, the scenario is different for multimeric proteins, which require coexpression of all the subunits to elicit their functional characteristics (5–8). Similarly, although certain proteins, involved in cell signaling, for instance, may independently be expressed, the biological effects of the expressed proteins can only be ascertained by their interactions with other proteins. Production of biologically active multimeric recombinant proteins has been difficult because of a lack of simple procedures for the coexpression of all the required subunits in each of the expressing host cell. Whereas expression of such multimeric proteins in yeast can be accomplished easily as a result of the availability of multiple auxotrophic yeast strains and vector DNAs, the formidable and inefficient yeast cell-wall breakage procedures greatly reduce the recovery of the expressed proteins to unacceptable levels for any structural or functional analyses (9). The focus of our laboratory is to understand the amiloride-sensitive epithelial Na⁺ channel (ENaC)-mediated Na⁺ transport (10,11).