Structure-Activity Relationships of Ligand Binding to Oxysterol-Binding Protein (OSBP) and OSBP-Related Protein 4.

Oxysterol-binding protein (OSBP) and OSBP-related protein 4 (ORP4) have emerged as potentially druggable targets in antiviral and precision cancer drug development. Multiple structurally diverse small molecules function through targeting the OSBP/ORP family of proteins, including the antiviral steroidal compounds OSW-1 and T-00127-HEV2. Here, the structure-activity relationships of oxysterols and related compound binding to human OSBP and ORP4 are characterized. Oxysterols with hydroxylation at various side chain positions (i.e., C-20, C-24, C-25, and C-27)─but not C-22─confer high affinity interactions with OSBP and ORP4. A library of 20(S)-hydroxycholesterol analogues with varying sterol side chains reveal that side chain length modifications are not well tolerated for OSBP and ORP4 interactions. This side chain requirement is contradicted by the high affinity binding of T-00127-HEV2, a steroidal compound lacking the side chain. The binding results, in combination with docking studies using homology models of OSBP and ORP4, suggest multiple modes of steroidal ligand binding to OSBP and ORP4.

Modulating the nitrite reductase activity of globins by varying the heme substituents: Utilizing myoglobin as a model system.

Globins, such as hemoglobin (Hb) and myoglobin (Mb), have gained attention for their ability to reduce nitrite (NO2(-)) to nitric oxide (NO). The molecular interactions that regulate this chemistry are not fully elucidated, therefore we address this issue by investigating one part of the active site that may control this reaction. Here, the effects of the 2,4-heme substituents on the nitrite reductase (NiR) reaction, and on the structures and energies of the ferrous nitrite intermediates, are investigated using Mb as a model system. This is accomplished by studying Mbs with hemes that have different 2,4-R groups, namely diacetyldeuteroMb (-acetyl), protoMb (wild-type (wt) Mb, -vinyl), deuteroMb (-H), and mesoMb (-ethyl). While trends on the natural charge on Fe and O-atom of bound nitrite are observed among the series of Mbs, the Fe(II)-NPyr (Pyr=pyrrole) and Fe(II)-NHis93 (His=histidine) bond lengths do not significantly change. Kinetic analysis shows increasing NiR activity as follows: diacetyldeuteroMb

Binding interaction of hypocrellin B to myoglobin: a spectroscopic and computational study.

Hypocrellin B (Hyp B), a perylenequinone naturally present in Hypocrella bambusae, is commonly used to treat a variety of diseases. Its versatile role in different biomedical applications necessitates a thorough investigation of its interaction with different biomolecules, particularly enzymes. To address this need, the binding mode of Hyp B to myoglobin (Mb) was studied using UV-visible absorption, emission, and synchronous fluorescence spectroscopies, as well as flexible docking simulations. Analyses of the absorbance and fluorescence data establish that Hyp B quenches tyrosine (Tyr) and tryptophan (Trp) fluorescence via the formation of two unique ground-state complexes on the surface of Mb, with one site being more energetically preferred than the other (the fraction of fluorophores accessible by Hyp B is 0.32). Molecular modeling simulations demonstrate preferential Hyp B binding at the Tyr103 site first, followed by the Trp7 site. In both cases, a ground-state complex is generated through H-bonding interaction between Hyp B and the respective residues, with the Tyr103 complex being more stable than that of the Trp7 complex. Synchronous fluorescence measurements indicate that the microenvironment surrounding Trp7 becomes more hydrophilic upon Hyp B interaction. This is evidenced by a red-shift of the band associated with this residue, while that of Tyr103 remains the same. Electrostatic potential surfaces reveal a more pronounced shift in electron density of Trp7 upon Hyp B binding compared to Tyr103. The binding constant of Hyp B to Mb is 1.21×10(5)M(-1), suggesting a relatively strong interaction between the ligand and enzyme.