First Insights on Organic Cosolvent Effects on FhuA Wildtype and FhuA Δ1-159

Circular dichroism (CD) and deconvolution were used to study the structural integrity of a plugged and an open FhuA transmembrane channel protein in the presence of varied concentrations of tetrahydrofuran (THF), ethanol (EtOH) and chloroform/methanol (C/M). FhuA is an Escherichia coli outer membrane protein (78.9 kDa) consisting of 22 beta-sheets and an internal globular cork domain which acts as an iron transporter. FhuA and the deletion variant FhuA Delta 1-159 showed comparable and remarkable resistance in the presence of THF (<= 40 vol%) and EtOH (<= 10 vol%). In C/M, significant differences in structural resistance were observed (FhuA stable <= 10 vol%; FhuA Delta 1-159 <= 1 vol%). Deconvolution of CD-spectra for FhuA and FhuA Delta 1-159 yielded beta-sheet contents of 61 % (FhuA) and 58% (FhuA Delta 1-159). Interestingly, FhuA and FhuA Delta 1-159 had comparable beta-sheet contents in the presence and absence of all three organic cosolvents. Additionally, precipitated FhuA and FhuA Delta 1-159 (in 40 vol% C/M or 65 vol% THF) redissolved by supplementing the detergent n-octyl-oligo-oxyethylene (oPOE).