No abstract

Ester bond hydrolysis of membrane phospholipids by Phospholipase A2 and consequent release of fatty acids are the initiating steps of inflammation. It is proposed in this study that the inhibition of phospholipase A2 is one of the ways to control inflammation. Investigations are carried out to identify the mode of inhibition of phospholipase A2 by the n‐hexadecanoic acid. It may help in designing of specific inhibitors of phospholipase A2 as anti‐inflammatory agents. The enzyme kinetics study proved that n‐hexadecanoic acid inhibits phospholipase A2 in a competitive manner. It was identified from the crystal structure at 2.5 Å resolution that the position of n‐hexadecanoic acid is in the active site of the phospholipase A2. The binding constant and binding energy have also been calculated using Isothermal Titration Calorimetry. Also, the binding energy of n‐hexadecanoic acid to phospholipase A2 was calculated by in silico method and compared with known inhibitors. It may be concluded from the structural and kinetics studies that the fatty acid, n‐hexadecanoic acid, is an inhibitor of phospholipase A2, hence, an anti‐inflammatory compound. The inferences from the present study validate the rigorous use of medicated oils rich in n‐hexadecanoic acid for the treatment of rheumatic symptoms in the traditional medical system of India, Ayurveda.

The three-dimensional structure of the diferric form of human lactoferrin has been refined at 2.2 A resolution, using synchrotron data combined with a lower resolution (3.2 A) diffractometer data set. Following restrained least-squares refinement and model rebuilding the final model comprises 5330 protein atoms (691 residues), 2Fe(3+) and 2CO(3)(2-) ions, 469 solvent molecules and 98 carbohydrate atoms (eight sugar residues). Root-mean-square deviations from standard geometry are 0.015 A for bond lengths and 0.038 A for angle (1-3) distances, and the final crystallographic R-factor is 0.179 for all 39 113 reflections in the resolution range 8.0-2.2 A. A close structural similarity is seen between the two lobes of the molecule, with differences mainly in loops and turns. The two binding sites are extremely similar, the only apparent differences being a slightly more asymmetric bidentate binding of the carbonate ion to the metal, and a slightly longer Fe-O bond to one of the Tyr ligands, in the N-lobe site relative to the C-lobe site. Distinct differences are seen in the interactions made by two cationic groups, Arg210 and Lys546, behind the iron site, and these may influence the stability of the two metal sites. Analysis of interdomain and interlobe interactions shows that these are few in number which is consistent with the known flexibility of the molecule with respect to domain and lobe movements. Internal water molecules are found in discrete sites and in two large clusters (in the two interdomain clefts) and one tightly bound water molecule is present 3.8 A from the Fe atom in each lobe. The carbohydrate is weakly defined and has been modelled to a limited extent; two sugar residues of the N-lobe glycan and six of the C-lobe glycan. Only one direct protein-carbohydrate contact can be found.

Background The nasal carriage of SARS-CoV-2 has been reported as the key factor transmitting COVID-19. Interventions that can reduce viral shedding from the nasopharynx could potentially mitigate the severity of the disease and its contagiousness. Herbal formulation of Citrus medica and Zingiber officinale is recommended in an Ayurvedic text as a nasal rinse in the management of contagious fevers. These herbs are also indicated in the management of respiratory illnesses and have been attributed with activity against pathogenic organisms in other texts. Molecular docking studies of the phytocompounds of C. medica and Z. officinale were done to find out whether these compounds could inhibit the receptor binding of SARS-CoV-2 spike protein (S protein) as well as the angiotensin-converting enzyme 2 (ACE-2), as evidenced from their docking into binding/active sites. Results The proteins of SARS-CoV-2, essential for its entry into human cells and highly expressed in the goblet and ciliated cells of nasal epithelium, play a significant role in contagiousness of the virus. Docking studies indicated that the specific compounds present in C. medica and Z. officinale have significant affinity in silico to spike protein of virus and ACE-2 receptor in the host. Conclusion In silico studies suggest that the phytochemical compounds in C. medica and Z. officinale may have good potential in reducing viral load and shedding of SARS-CoV-2 in the nasal passages. Further studies are recommended to test its efficacy in humans for mitigating the transmission of COVID-19.