The effect of membrane composition on the interaction between human CYP51 and its flavonoid inhibitor - luteolin 7,3'-disulfate

Cytochromes P450 (CYP) are a family of membrane proteins involved in the production of endogenous molecules and the metabolism of xenobiotics. It is well-known that the composition of the membrane can influence the activity and orientation of CYP proteins. However, little is known about how membrane composition affects the ligand binding properties of CYP. In this study, we utilized surface plasmon resonance and fluorescence lifetime analysis to examine the impact of membrane micro-environment composition on the interaction between human microsomal CYP51 (CYP51A1) and its inhibitor, luteolin 7,3'-disulphate (LDS). We observed that membranes containing cholesterol or sphingomyelin exhibited the lowest apparent equilibrium dissociation constant for the CYP51A1-LDS complex. Additionally, the tendency for relation between kinetic parameters of the CYP51A1-LDS complex and membrane viscosity and overall charge was observed. These findings suggest that the specific composition of the membrane, particularly the presence of cholesterol and sphingomyelin, plays a vital role in regulating the interaction between CYP enzymes and their ligands.

New APETx-like peptides from sea anemone Heteractis crispa modulate ASIC1a channels

Sea anemones are an abundant source of various biologically active peptides. The hydrophobic 20% ethanol fraction of tropical sea anemone Heteractis crispa was shown to contain at least 159 peptide compounds including neurotoxins, proteinase and α-amylase inhibitors, as well as modulators of acid-sensing ion channels (ASICs). The three new peptides, π-AnmTX Hcr 1b-2, -3, and -4 (41 aa) (short names Hcr 1b-2, -3, -4), identified by a combination of reversed-phase liquid chromatography and mass spectrometry were found to belong to the class 1b sea anemone neurotoxins. The amino acid sequences of these peptides were determined by Edman degradation and tandem mass spectrometry. The percent of identity of Hcr 1b-2, -3, and -4 with well-known ASIC3 inhibitors Hcr 1b-1 from H. crispa and APETx2 from Anthopleura elegantissima is 95-78% and 46-49%, respectively. Electrophysiological experiments on homomeric ASIC channels expressed in Xenopus laevis oocytes establish that these peptides are the first inhibitors of ASIC1a derived from sea anemone venom. The major peptide, Hcr 1b-2, inhibited both rASIC1a (IC₅₀ 4.8 ± 0.3 μM; nH 0.92 ± 0.05) and rASIC3 (IC₅₀ 15.9 ± 1.1 μM; nH 1.0 ± 0.05). The maximum inhibition at saturating peptide concentrations reached 64% and 81%, respectively. In the model of acid-induced muscle pain Hcr 1b-2 was also shown to exhibit an antihyperalgesic effect, significantly reducing of the pain threshold of experimental animals.