Self-assembly And Mechanism Of Polyoxometalates With The Peptides From Human Papillomavirus Capsid Protein L1

Polyoxometalates (POMs) are a typical class of metal-oxygen anionic clusters. Theirunique electronic, optical, magnetic and redox properties lead to attractive applications in avariety fields such as nanotechnology, photochemistry, catalysis and so on. On the other hand,POMs are found to have biological activities and have been tried to use in biological systems,such as antibacteria, antivirus, anticancer and so forth, which attracted more research interestin the past two decades.Human papillomavirus (HPVs) are a family of non-enveloped double-stranded DNAviruses that infect epithelial cells in the skin and mucosa, and have attracted extensivelyattentions recently because of their high hazard for human health. Both epidemiologic andbiochemical studies indicate that infection with certain high-risk types of HPV is directlyassociated with anogenital malignancies, particularly the cervical cancer.Recently, it is recognized that POM can induce cell apoptosis, inhibit aggregation ofamyloid peptides. Apparently, clarification the molecular interaction between POMs andspecific proteins are the critical step towards understanding the bio-functions. The reportedinvestigations on POMs-protein interactions have illustrated that the binding between themare mainly dependent on favourable electrostatic attraction and POM size effects, which aregenerally robust but not specific. Few studies have dealt with the selective recognition ofPOMs to specific binding site or peptidic segments including in the functional proteins.Therefore, figuring out the special association of POM with representative peptides insolution will benefit for understanding the locations and specific sites of the interactionbetween POMs and proteins. The interactions of several arginine-and lysine-rich peptides ofHPV-16and HPV-18capsid proteins, called nuclear localization signals (NLS), with thenegatively charged cell surface receptor heparan/heparin have been reported forunderstanding the infection of virus particles to host cells. To recognize the binding generatedchange of protein assembly structure and to find out a possible POM inhibitor, we hereininvestigate the highly charged POM binding NLS peptides toward revealing the selectiverecognition to HPVs capsid protein for possible antiviral mechanism in the future work.In the present study, we chose two polyoxometalates (EuW10and EuSiWMo) and twohigh risk type peptides from human papillomavirus capsid protein L1(HPV18Ctb and HPV16Ctb), hope that through the study of the interaction and mechanism between themextend the understanding of the interactions of POMs with proteins. Furthermore, theclarification of binding mechanism between POMs and the peptides at molecular level wouldpromote to understand the biological activity of inorganic chemicals, either to promote designof multi-functional targeting agents for future virus treatment.In the first part work, through a self-assembly of arginine/lysine-rich peptide from HPVcapsid protein and an Eu-containing polyoxometalate (Na9[EuW10O36]·32H2O), nanosphereswhich formation in the aqueous solution was presented, in showing large luminescenceenhancement of POM and can be used as a potential “turn-on” fluorescence probe in biology.The binding mechanisms between them have been explored at molecular level by using TEM,SEM, fluorescence spectra, ITC, zeta-potential and1H NMR titration spectra. ITC studyconfirmed the assembly was completely enthalpy driven, zeta-potential proved that thedriving force was governed mainly by the electrostatic interaction,1H NMR spectroscopyindicated changes in hydrogen-bond of EuW10and the peptide segment, and the bindingmodel were clarified finally. Our design constructed the self-assembly fabrication ofwell-defined nanoparticles by using inorganic POM and bio-applicable peptide, and especiallyit combined with strong fluorescence characterization together. The enhanced luminescenceand specific targeted-HPV peptide ability would be important and useful in the detection ofHPV capsid protein and/or HPV genotypes. Therefore, the present report will be helpful topromote the development of anti-virus agents in future.In the second part work, a two-step assembly of a peptide from HPV16L1with a highlycharged europium-substituted polyoxometalate (K13[Eu(SiW10MoO39)2]·28H2O, EuSiWMo)cluster, accompanying a great luminescence enhancement of the inorganic polyanions, isreported. The mechanism is discussed in detail by analyzing the thermodynamic parametersfrom isothermal titration calorimetry, the time-resolved fluorescent and NMR spectra. Bycomparing the actions of the peptide analogues, the binding process and model are proposedaccordingly. The driving forces in each binding step are clarified, and the initial POMaggregation, basic-sequence and hydrophobic C-termini of peptide are revealed to contributeto the two-step assembly. It should be noted, the highly charged EuSiWMo might bring newinteraction force when binding with peptides or proteins, which were not take much ofattention in the previous investigations. Therefore, the present study demonstrates both ameaningful preparation for biocompatible inorganic materials and a strategy using POMs tomodulate the assembly of peptides and even proteins, which could be extended to otherproteins and/or viruses by using the peptides and POMs with similar properties, and therefore, will promote the future treatment of virus.