We present a brief review of our recent computational studies of hydrogen bonds (H-bonds) in helical secondary structures of proteins, α-helix and 3₁₀-helix, using a Negative Fragmentation Approach with density functional theory. We found that the depolarized electronic structures of the carbonyl oxygen of the ith residue and the amide hydrogen of the (i + 4)th residue cause weaker H-bond in an α-helix than in an isolated H-bond. Our calculations showed that the H-bond energies in the 3₁₀-helix were also weaker than those of the isolated H-bonds. In the 3₁₀-helices, the adjacent N–H group at the (i + 1)th residue was closer to the C=O group of the H-bond pair than the adjacent C=O group in the 3₁₀-helices, whereas the adjacent C=O group at the (i + 1)th residue was close to the H-bond acceptor in α-helices. Therefore, the destabilization of the H-bond is attributed to the depolarization caused by the adjacent residue of the helical backbone connecting the H-bond donor and acceptor. The differences in the change in electron density revealed that such depolarizations were caused by the local electronic interactions in their neighborhood inside the helical structure and redistributed the electron density. We also present the improvements in the force field of classical molecular simulation, based on our findings.

Heme participates in a wide range of biological functions such as oxygen transport, electron transport, oxygen reduction, transcriptional regulation and so on. While the mechanism of each function has been investigated for many heme proteins, the origin of the diversity of the heme functions is still unclear and a crucial scientific issue. We have constructed a database of heme proteins, named Python-based database and analyzer for DIStortion of Heme porphyrin (PyDISH), which also contains some analysis tools. The aim of PyDISH is to integrate the information on the structures of hemes and heme proteins and the functions of heme proteins. This database will provide the structure–function relationships focusing on heme porphyrin distortion and lead to the elucidation of the origin of the functional diversity of heme proteins. In addition, the insights obtained from the database can be used for the design of protein function. PyDISH contains the structural data of more than 13 000 hemes extracted from the Protein Data Bank, including heme porphyrin distortion, axial ligands coordinating to the heme and the orientation of the propionate sidechains of heme. PyDISH also has information about the protein domains, including Uniprot ID, protein fold by CATH ID, organism, coordination distance and so on. The analytical tools implemented in PyDISH allow users to not only browse and download the data but also analyze the structures of heme porphyrin by using the analytical tools implemented in PyDISH. PyDISH users will be able to utilize the obtained results for the design of protein function. Database URL: http://pydish.bio.info.hiroshima-cu.ac.jp/

Hydrogen‐bond (H‐bond) interaction energies in α‐helices of short alanine peptides were systematically examined by precise density functional theory calculations, followed by a molecular tailoring approach. The contribution of each H‐bond interaction in α‐helices was estimated in detail from the entire conformation energies, and the results were compared with those in the minimal H‐bond models, in which only H‐bond donors and acceptors exist with the capping methyl groups. The former interaction energies were always significantly weaker than the latter energies, when the same geometries of the H‐bond donors and acceptors were applied. The chemical origin of this phenomenon was investigated by analyzing the differences among the electronic structures of the local peptide backbones of the α‐helices and those of the minimal H‐bond models. Consequently, we found that the reduced H‐bond energy originated from the depolarizations of both the H‐bond donor and acceptor groups, due to the repulsive interactions with the neighboring polar peptide groups in the α‐helix backbone. The classical force fields provide similar H‐bond energies to those in the minimal H‐bond models, which ignore the current depolarization effect, and thus they overestimate the actual H‐bond energies in α‐helices. © 2019 The Authors. Journal of Computational Chemistry published by Wiley Periodicals, Inc.

AlphaFold3 can predict protein–ligand complex structures. In this study, we examined the accuracy of prediction of heme–protein interactions by AlphaFold3. AlphaFold3 succeeded in predicting heme–protein interactions for most heme proteins except for those without homologous proteins in the Protein Data Bank. Our comparison of predictions by AlphaFold3 and AlphaFold2 suggests that heme–protein structures can be predicted from amino acid sequences of proteins alone using AlphaFold2.

Heme is located in the active site of proteins and has diverse and important biological functions, such as electron transfer and oxygen transport and/or storage. The distortion of heme porphyrin is considered an important factor for the diverse functions of heme because it correlates with the physical properties of heme, such as oxygen affinity and redox potential. Therefore, clarification of the relationship between heme distortion and the protein environment is crucial in protein science. Here, we analyzed the fluctuation in heme distortion in the protein environment for hemoglobin and myoglobin using molecular dynamics (MD) simulations and quantum mechanical (QM) calculations as well as statistical analysis of the protein structures of hemoglobin and myoglobin stored in Protein Data Bank. Our computation and statistical analysis showed that the protein environment for hemoglobin and myoglobin prominently affects the doming distortion of heme porphyrin, which correlates with its oxygen affinity, and that the magnitude of distortion is different between hemoglobin and myoglobin. These results suggest that heme distortion is affected by its protein environment and fluctuates around its fitted conformation, leading to physical properties that are appropriate for protein functions.