Imidazole Nitrogens of Two Histidine Residues Participating in N–H···N Hydrogen Bonds in Protein Structures: Structural Bioinformatics Approach Combined with Quantum Chemical Calculations
Protein structures are stabilized by different types of hydrogen bonds. However, unlike the DNA double helical structure, the N–H···N type of hydrogen bonds is relatively rare in proteins. N–H···N hydrogen bonds formed by imidazole groups of two histidine residues have not been investigated. We have systematically analyzed 5333 high-resolution protein structures with resolution 1.8 Å or better and identified 285 histidine pairs in which the nitrogen atoms of the imidazole side chains can potentially participate in N–H···N hydrogen bonds. The histidine pairs were further divided into two groups, neutral–neutral and protonated–neutral, depending on the protonation state of the donor histidine. Quantum chemical calculations were performed on imidazole groups adopting the same geometry observed in the protein structures. Average interaction energies between the interacting imidazole groups are −6.45 and −22.5 kcal/mol for neutral–neutral and protonated–neutral, respectively. Hydrogen bond interaction between ...
Abhishek Hariharan Iyer; R. N. V. Krishna Deepak; Ramasubbu Sankararamakrishnan
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