Screening of the Protein Data Bank led to identification of a recurring structural motif where lysine NH3 + group interacts with backbone carbonyl. This interaction is characterized by linear atom arrangement, with carbonyl O atom positioned on the three-fold symmetry axis of the NH3 + group (angle Cε-Nζ-O close to 180°, distance Nζ-O ca. 2.7-3.0 Å). Typically, this linear arrangement coexists with three regular hydrogen bonds formed by lysine NH3 + group (angle Cε-Nζ-acceptor atom close to 109°, distance Nζ-acceptor atom ca. 2.7-3.0 Å). Our DFT calculations using polarizable continuum environment suggest that this newly identified linear interaction makes an appreciable contribution to protein’s energy balance, up to 2 kcal/mol. In the context of protein structure, linear interactions play a role in capping the C-termini of α-helices and 310-helices. Of note, linear interaction involving conserved lysine is consistently found in the P-loop of numerous NTPase domains, where it stabilizes the substrate-binding conformation of the P-loop. Linear interaction NH3 + – carbonyl represents an interesting example of ion-dipole interactions that has so far received little attention compared to ion-ion interactions (salt bridges) and dipole-dipole interactions (hydrogen bonds), but nevertheless represents a distinctive element of protein architecture.
Rogacheva, O. N., Izmailov, S. A., Slipchenko, L. V., & Skrynnikov, N. R. (2017). A new structural arrangement in proteins involving lysine NH3+ group and carbonyl. Scientific Reports, 7(1), 16402. https://doi.org/10.1038/s41598-017-16584-y