Scalaradial, a Dialdehyde‐Containing Marine Metabolite That Causes an Unexpected Noncovalent PLA₂ Inactivation

Abstract

Several marine terpenoids that contain at least one reactive aldehyde group, such as manoalide and its congeners, possess interesting anti-inflammatory activities that are mediated by the covalent inactivation of secretory phospholipase A(2) (sPLA(2)). Scalaradial, a 1,4-dialdehyde marine terpenoid that was isolated from the sponge Cacospongia mollior, is endowed with a relevant anti-inflammatory profile, both in vitro and in vivo, through selective sPLA(2) inhibition. Due to its peculiar dialdehyde structural feature, it has been proposed that scalaradial exerts its enzymatic inactivation by means of an irreversible covalent modification of its target. In the context of our on-going research on anti-PLA(2) natural products and their interaction at a molecular level, we studied scalaradial in an attempt to shed more light on the molecular mechanism of its PLA(2) inhibition. A detailed analysis of the reaction profile between scalaradial and bee venom PLA(2), a model sPLA(2) that shares a high structural homology with the human synovial enzyme, was performed by a combination of spectroscopic techniques, chemical reactions (selective modifications, biomimetic reactions), and classical protein chemistry (such as proteolytic digestion, HPLC and mass spectrometry), along with molecular modeling studies. Unexpectedly, our data clearly indicated the noncovalent forces to be the leading event in the PLA(2) inactivation process; thus, the covalent modification of the enzyme emerges as only a minor side event in the ligand-enzyme interaction. The overall picture might be useful in the design of SLD analogues as new potential anti-inflammatory compounds that target sPLA(2) enzymes.

Recent developments in anti‐inflammatory natural products

“…180 Due to its peculiar dialdehyde structural feature, it has been proposed that scalaradial exerts PLA 2 enzymatic inactivation by means of an irreversible covalent modification of its target. 220 Scalaradial also exerted an inhibitory effect on HL-60 cells proliferation, and inhibited the epidermal growth factor receptor (EGFR)-mediated Akt phosphorylation, and this effect was found to be independent of sPLA 2 . 221 Scalaradial showed an interesting finding in BEL-7402 cells by exhibiting the inhibition of ERK1/2 phosphorylation in early stage and stimulation of ERK1/2 phosphorylation in the later stage of its treatment, which displayed its biphasic regulatory responses.…”

Quantum mechanical binding free energy calculation for phosphopeptide inhibitors of the Lck SH2 domain

“…refs. [81][82][83] for methodological details of the Monte Carlo sampling). If all conformers were equally visited, and the bound state was characterized by a single conformation, the conformational entropy change on binding would be RTln100 5 2.8 kcal/mol, significantly smaller than the rigid body and vibrational entropies (cf.…”

The Binding Mode of Cladocoran A to the Human Group IIA Phospholipase A2

“…As already carried out in our previous studies on sPLA 2 , [13][14][15][16][17][21][22][23] we started with the analysis of sPLA 2 potential covalent modification by CLD A through liquid chromatography-nano-ESI MS (LC-nano-ESI-MS). Time-course analysis of the CLD A and sPLA 2 -IIA reaction mixture was performed, and the chromatograms revealed the presence of the unmodified sPLA 2 -IIA (M W 13 860.05(AE0.45) Da) and of a species corresponding to a 1:1 sPLA 2 -IIA-CLD A covalent adduct with a mass increment of approximately 384 Da ( Figure 1 and Table 1).…”

“…As we wanted to determine the role of the noncovalent interactions in sPLA 2 -IIA inactivation by CLD A, we resorted to the use of p-nitrophenacyl bromide (pNBr, M W = 244 Da), a well-known specific ligand of the catalytic His resi- [17,[22][23][24] Indeed, comparative pNBr modification experiments in the presence and absence of a given inhibitor provides valuable clues about the inhibition mechanism (if competitive or not). We incubated sPLA 2 -IIA in the presence of pNBr and detected by LC-MS a significant amount of sPLA 2 -IIA covalently modified by this agent (Figure 2, back).…”