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The better tag remains unseen.

One of the most crucial steps in protein structure determination by nuclear magnetic resonance (NMR) spectroscopy is the preparation of highly concentrated and well behaving protein samples. Here we present a system of modular tags which allows for high level expression, sophisticated purification of full-length protein, and solubility enhancement while keeping the amount of additional resonances low. This system consists of two different expression constructs and utilizes the tight binding of human calmodulin (hCaM) to the calmodulin binding peptide (CBP), which has already been used as a purification tag.