Nucleotide binding kinetics and conformational change analysis of tissue transglutaminase with switchSENSE.

Function, activity, and interactions of proteins crucially depend on their three-dimensional structure and are often regulated by effector binding and environmental changes. Tissue transglutaminase (Transglutaminase 2, TG2) is a multifunctional protein, allosterically regulated by nucleotides and Ca2+ ions, which trigger opposing conformational changes. Here we introduce switchSENSE as a versatile tool for TG2 characterization and provide novel insights into protein conformation as well as analyte binding kinetics. For the first time, we succeeded in measuring the kinetic rate constants and affinities (k on , k off , K D) for guanosine nucleotides (GMP, GDP, GTP, GTPγS). Further, the conformational changes induced by GDP, Ca2+ and the covalent inhibitor Z-DON were observed by changes in TG2's hydrodynamic diameter. We confirmed the well-known compaction by guanosine nucleotides and extension by Ca2+, and provide evidence for TG2 conformations so far not described by structural analysis. Moreover, we analyze the influence of the peptidic Z-DON inhibitor and the R580A mutation on the conformational responsiveness of TG2 to its natural effectors. In summary, this work shows how the combination of structural and kinetic information obtained by switchSENSE opens new perspectives for the characterization of conformationally active proteins and their interactions with ligands, e.g. potential drug candidates. Image 1 • Introduction of switchSENSE as a tool for the characterization of TG2 interaction kinetics and conformational changes. • TG2 – guanosine nucleotide binding kinetics (k on , k off , K D) were resolved for the first time. • Conformational dynamics of TG2 is governed by multiple (at least two) mechanisms. • Direct proof that inhibition of TG2 with Z-DON requires Ca2+. • TG2's active conformation in presence of Ca2+ is not equivalent to the inhibitor bound Ca2+-free ("open") conformation. [ABSTRACT FROM AUTHOR]