Optimized procedure to generate heavy isotope and selenomethionine-labeled proteins for structure determination using Escherichia coli-based expression systems

摘要

Generating sufficient quantities of labeled proteins represents a bottleneck in protein structure determination. A simple protocol for producing heavy isotope as well as selenomethionine (Se-Met)-labeled proteins was developed using T7-based Escherichia coli expression systems. The protocol is applicable for generation of single-, double-, and triple-labeled proteins (~(15)N, ~(13)C, and ~2H) in shaker flask cultures. Label incorporation into the target protein reached 99% and 97% for ~(15)N and ~(13)C, respectively, and 75% of (non-exchangeable) hydrogen for ~2H labeling. The expression yields and final cell densities (OD600 ～16) were the same as for the production of non-labeled protein. This protocol is also applicable for Se-Met labeling, leading to Se-Met incorporation into the target protein of 70% or 90% using prototrophic or methionine auxotrophic E. coli strains, respectively.