Sequence-level prediction and control of the production of a membrane protein

Abstract

Integral membrane proteins (IMP) play crit. cellular roles by controlling the flow of information and nutrients across lipid bilayers, yet mechanistic understanding of IMPs is hindered by difficulties in IMP expression. We provide evidence that IMP expression can be understood and controlled at the amino-acid level. For homologs of the IMP TatC, obsd. expression levels vary widely and are affected by small changes in protein sequence. A key step in IMP expression is insertion of the IMP into the lipid membrane via the Sec translocon, a minutetimescale process that takes place during IMP synthesis by the ribosome. Computational modeling of Sec facilitated co-translational integration reveals a strong correlation between the effect of mutations on the exptl. obsd. expression levels and on calcd. efficiency of membrane integration. We further demonstrate that calcd. integration efficiency can be used to det. sequence modifications that increase the exptl. obsd. expression levels. Reprodn. of these trends in both Escherichia coli and Mycobacterium smegmatis suggests that the results are general to other expression systems. This work indicates that IMP expression can be enhanced via rational design, potentially enabling the expansion of accessible IMP systems.