The influence of commonly used tags on structural propensities and internal dynamics of peptides

The influence of biotin and fluorescein tags attached to the N-terminus of peptides on their structural propensities is assessed by NMR methods. While the small peptides investigated are highly mobile with no uniquely preferred conformation, the introduction of the tags, in particular hydrophobic ones, clearly shows an influence on NMR parameters such as chemical shifts and relaxation properties, which are not restricted to the nearby residues, but also affect distant parts. Thus, long-range effects on structural propensities become evident and are cause for concern with respect to the interpretation of weak interaction tests, which rely upon the assumption that tags do not exert influence on intermolecular interactions.