RESUMEN
The heterologous overexpression of integral membrane proteins in Escherichia coli often yields insufficient quantities of purifiable protein for applications of interest. The current study leverages a recently demonstrated link between co-translational membrane integration efficiency and protein expression levels to predict protein sequence modifications that improve expression. Membrane integration efficiencies, obtained using a coarse-grained simulation approach, robustly predicted effects on expression of the integral membrane protein TatC for a set of 140 sequence modifications, including loop-swap chimeras and single-residue mutations distributed throughout the protein sequence. Mutations that improve simulated integration efficiency were 4-fold enriched with respect to improved experimentally observed expression levels. Furthermore, the effects of double mutations on both simulated integration efficiency and experimentally observed expression levels were cumulative and largely independent, suggesting that multiple mutations can be introduced to yield higher levels of purifiable protein. This work provides a foundation for a general method for the rational overexpression of integral membrane proteins based on computationally simulated membrane integration efficiencies.
Asunto(s)
Proteínas de Escherichia coli/metabolismo , Escherichia coli/metabolismo , Membrana Dobles de Lípidos/metabolismo , Proteínas de Transporte de Membrana/metabolismo , Simulación de Dinámica Molecular , Proteínas de Escherichia coli/genética , Proteínas de Transporte de Membrana/genética , Mutación Puntual , Unión Proteica , Transporte de ProteínasRESUMEN
Integral membrane proteins (IMPs) control the flow of information and nutrients across cell membranes, yet IMP mechanistic studies are hindered by difficulties in expression. We investigate this issue by addressing the connection between IMP sequence and observed expression levels. For homologs of the IMP TatC, observed expression levels vary widely and are affected by small changes in protein sequence. The effect of sequence changes on experimentally observed expression levels strongly correlates with the simulated integration efficiency obtained from coarse-grained modeling, which is directly confirmed using an in vivo assay. Furthermore, mutations that improve the simulated integration efficiency likewise increase the experimentally observed expression levels. Demonstration of these trends in both Escherichia coli and Mycobacterium smegmatis suggests that the results are general to other expression systems. This work suggests that IMP integration is a determinant for successful expression, raising the possibility of controlling IMP expression via rational design.
Asunto(s)
Membrana Celular/metabolismo , Proteínas de Escherichia coli/química , Escherichia coli/genética , Regulación Bacteriana de la Expresión Génica , Proteínas de la Membrana/química , Proteínas de Transporte de Membrana/química , Mycobacterium smegmatis/genética , Secuencia de Aminoácidos , Membrana Celular/química , Clonación Molecular , Escherichia coli/metabolismo , Proteínas de Escherichia coli/genética , Proteínas de Escherichia coli/metabolismo , Proteínas de la Membrana/genética , Proteínas de la Membrana/metabolismo , Proteínas de Transporte de Membrana/genética , Proteínas de Transporte de Membrana/metabolismo , Modelos Moleculares , Mycobacterium smegmatis/metabolismo , Conformación Proteica en Hélice alfa , Dominios y Motivos de Interacción de Proteínas , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Alineación de Secuencia , Homología de Secuencia de AminoácidoRESUMEN
We report a fluorescence-based turn-on sensor for mapping the mechanical strain exerted by specific cell-surface proteins in living cells. The sensor generates force maps with high spatial and temporal resolution using conventional fluorescence microscopy. We demonstrate the approach by mapping mechanical forces during the early stages of regulatory endocytosis of the ligand-activated epidermal growth factor receptor (EGFR).
