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Ovalbumin (OVA) is the most abundant protein in chicken egg white. It is one of the major allergens in eggs. Micro- and nanoplatic particles (MNPs) are a widespread contaminant and have been found in food and water. It is still unclear how MNPs might affect human health. However, due to their large surface area they have been found to bind various biopolymers, including proteins. These biopolymers can be bound more strongly or loosely, and are referred to as hard and soft corona, respectfully [1]. MPs have been found in eggs, in the size range of 50-100 μm [2]. It is shown that these particles can interact with proteins and induce structural changes, but there is still not enough information on this topic [3]. These structural changes could lead to a decreased digestibility in the gastrointestinal tract, which could increase the immune response to known allergens. The aim of this study was to determine whether there are structural changes present in the OVA after incubation with two types of MPs – 120 μm polyethylene terephthalate (PET) and 120 μm polystyrene (PS) and whether they could influence digestion of OVA with gastrointestinal enzymes. 20 mg of MPs were incubated with 1.3 mg/mL ovalbumin for 4 h at room temperature in a 20 mM phosphate buffer at pH 7. Bulk ovalbumin was separated from the MPs by centrifugation and by filtration through a 0.22 μm PVDF filter. Soft corona was obtained by washing the MPs with water, and the MPs were later removed as described with bulk ovalbumin. Formation of amyloids was monitored with a Thioflavin T (ThT) assay at room temperature and after thermal treatment, and additional structural analysis was performed by circular dichroism (CD) spectrometry in the far-UV region. Thermal stability was also determined by spectrofluorimetry. Digestion with two proteases (pepsin and trypsin) was performed to determine whether there is a change in the gastrointestinal digestibility of OVA. Results from the ThT assay show that at room temperature there is no significant difference between the fluorescence emission obtained for all samples, with bulk OVA from both MPs showing a slight decrease. However, there is an increase of fluorescence after thermal treatment in all OVA samples, where OVA from the soft corona emits significantly less fluorescence than control and bulk samples for both types of MPs. Additionally, soft coronas have been shown to have more β-sheet content than other samples, which is more pronounced for OVA incubated with PET. For the heated samples there is a sharp change from α-helix to β-sheets in all the samples, but it is the most dramatic in the soft coronas. This could impose rigidity to the tertiary structure, which would explain why the ThT molecule does not bind as strongly. Despite differences in both the secondary and tertiary structure, the thermal stability is almost the same in all samples. Digestion of the samples shows that the soft corona incubated with PS tends to be more resistant to trypsin than other samples after 2 min, but it is not significant. For digestion with pepsin there is no difference between the samples. In conjunction with the previous results, which indicates a structural stabilisation of the soft corona at pH 7, it is not surprising that there is an increased resistance to trypsin, compared to pepsin which is a gastric enzyme and for which digestion is performed at an acidic pH. In conclusion, there is a structural change present in samples upon contact with MPs, particularly in the soft corona, of which the most pronounced is a decrease of α-helix content and increase in β-sheet content as determined by far-UV CD. This leads to a structural stabilization which could further impact the digestibility of the OVA protein and impact its allergenicity. However, this must be confirmed with further experiments. Acknowledgments: This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 965173. References: [1] M.P. Monopoli, C. Åberg, A. Salvati, K.A.Dawson, Nat. Nanotechnol., 7 (2012) 779-786. [2] Q. Liu, Z. Chen, Y. Chen, F. Yang, W. Yao, Y. Xie. Food Chem., 397 (2022) 133771. [3] P. Ju, Y. Zhang. Y. Zheng, F. Gao, F. Jiang, J. Li, C. Sun, Sci. Total Environ., 734 (2020) 139219.

Microplastic represents one of the major types of pollutants in modern era. Over several years of research in the field of microplastic, there are still many unknown gaps, including the effects and mechanisms of action of these particles on human health. Studies in this field conducted experiments on cells and human tissues or animals like rats and mice. While these studies suggest the toxic effects of microplastic, it is not clear if concentrations used for exposure are relevant for humans. Also, most of the studies used spherical polystyrene, which does not reflect well the diversity of microplastic particles found in nature. Another gap is lack of studies describing direct interactions of microplastics and proteins. While it is generally known that proteins form corona around microplastic particles, affinity studies and consequences on protein structure are usually missing. The aim of this work was to analyze interaction of a major egg white protein and allergen, ovalbumin to several to microplastic particles, including polystyrene (PS) of 120 and 500 μm in size and polyethylene terephthalate (PET) of 120 μm in size. Binding affinity was determined at both acidic, pH 3 and neutral, pH 7 conditions, at the room temperature, by measuring bulk ovalbumin concentration in supernatants at the equilibrium time. Several binding models, including Langmuir, Freundlich, Redlich–Peterson and Guggenheim-Anderson-de Boer (GAB), were used to determine binding parameters. The formation of soft and hard corona was analyzed according to the published protocol [1]. Structural analysis was performed using near and far-UV CD spectrometry. Obtained results showed that ovalbumin binds to both PS and PET. All binding models indicated that ovalbumin binds with higher affinity to tested microplastics on pH 3, compared to pH 7, with the highest affinity being calculated for PS 120 μm. Further analysis showed that ovalbumin forms both soft and hard corona onto the surface of all three microplastics. Structural alterations of ovalbumin as a consequence of its interaction with microplastic was shown to be both pH and microplastic type dependent. Also, more pronounced effect on its tertiary structure was observed, compared to secondary. At pH3, tertiary structure of bulk ovalbumin becomes destabilized, especially in the presence of PET 120 μm and PS 500 μm, while at pH 7, structural stabilization is observed, especially in the presence of PS 120 μm. Considering that the microplastic was discovered in eggs [2], obtained results suggest that direct interactions of native ovalbumin with microplastic particles could have influence on its structure and thus affect its techno-functional properties. Acknowledgments: This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 96517. References: [1] D. Magrì, P. Sánchez-Moreno, G. Caputo, F. Gatto, M. Veronesi, G. Bardi, T. Catelani, D. Guarnieri, A. Athanassiou, P.P. Pompa, D. Fragouli, ACS Nano, 12 (2018) 7690-7700. [2] Q. Liu, Z. Chen, Y. Chen, F. Yang, W. Yao, Y. Xie, Food Chemistry, 397 (2022) 133771

Ta na dijagnoza ljudi sa sumnjom na infekciju SARS-CoV-2 je od suštinskog zna aja za suzbijanje globalnog širenja COVID-19. Prisustvo SARS-CoV-2 može se otkriti RT-PCRom (otkriva RNK virusa) ili detekcijom prisustva virusnih antigena u biološkim te nostima ELISA-om ili sli nom tehnikom koje koriste antitela razvijena u životinjama. Cilj studije je bio uspostavljanje kvantitativnog testa koji se zasniva na koriš enju poliklonskih seruma za rutinsko odre ivanje koncentracije SARS-CoV-2 nukleokapsidnog proteina merenjam apsorbancije u standardnoj mikrotitarskoj plo ici sa 96 bunara. Za potrebe razvoja testa proizveden je rekombinantni N-protein i koriš en za proizvodnju antiseruma u miševima i ze evima. Proizvedeni antiserumi su pre iš eni i odre en im je titar. Poliklonskiantiserumi visokog afiniteta specifi ni za N-protein koriš eni su za razvoj ELISA testa specifi nog za ovaj protein. Test se zasniva na koriš enju poliklonskih seruma miševa koji su adherirani na dno bunara mikrotitarske plo ice za hvatanje N-proteina iz uzorka. Razli ite koncentracije rekombinantnog N-proteina su koriš ene za standardnu krivu za kvantifikaciju proteina. N-protein vezan za antitela miševa je detektovan ze jim poliklonskim serumom i anti-ze jim antitelom povezanim sa enzimom koji obezbe uje spektrofotometrijsko merenje. Uspešno smo razvili prototip ELISA testa za kvantifikaciju N-proteina sa granicom detekcije u opsegu od ng/mL. Prose na vrednost LOD za prototip ELISA testa za detekciju N-proteina je 9,2 ng/mL, dok je prose na vrednost LOQ 10,2 ng/mL. Pokazali smo da su proizvedeni poliklonski antiserumi pogodni za detekciju N-proteina sa sli nim ili boljim afinitetom i specifi noš u od komercijalnih antitela. Štaviše, prototip ELISA testa se može koristiti sa zadovoljavaju om pouzdanoš u za kvantifikaciju N-proteina u uzorcima bogatim proteinima, poput ljudskih seruma. The accurate diagnosis of people with suspected infection with the SARS-CoV-2 is essential to curb the global spread of COVID-19. The presence of SARS-CoV-2 can be detected by RT-PCR (it detects RNA of the virus) or by the presence of viral antigens in biological fluids in ELISA or similar techniques using antibodies developed in animals. The aim of the study was the establishment of a quantitative polyclonal sera-based test for routine measurement of the concentration of SARS CoV-2 nucleocapsid protein using absorbance measurement in a standard 96-well microtiter plate. For the purposes of the test development, recombinant N protein was produced and used for the production of mice and rabbit antisera. Produced antisera were purified and titer was determined. High-affinity polyclonal N-protein specific antisera were used for N-protein specific ELISA test development. The test is based on mice polyclonal sera adhered to microtiter plate bottom for the capture of the N protein from the specimen. Various concentrations of the recombinant N-protein were used to generate a standard curve for protein quantification. The N-protein bound to the mice antibodies was detected with rabbit polyclonal sera and anti-rabbit antibody coupled to an enzyme that provides spectrophotometric measurement. We have successfully developed the prototype ELISA for the quantification of N-protein with the detection limit being in the range of ng/mL. The average LOD value for the prototype ELISA was determined to be 9.2 ng/mL, while the average LOQ value was 10.2 ng/mL. We have demonstrated that produced polyclonal antisera are suitable for the detection of N-protein with affinity and specificity similar to, or better than commercial antibodies. Furthermore, the prototype ELISA can be used with satisfactory confidence for quantification of the N-protein in protein-rich samples, similar to human sera. Poster: [https://cherry.chem.bg.ac.rs/handle/123456789/5362]

The emergence of the coronavirus SARS-CoV-2 has attracted attention of the whole scientific community. The SARS-CoV-2 spike (S) protein plays the most important role in viral attachment to host receptor angiotensin-converting enzyme 2 (ACE2), via the receptor-binding domain (RBD), fusion and entry into the host, and it serves as a target for the development of antibodies, entry inhibitors and vaccines. It has been demonstrated that phycocyanobilin (PCB), a bioactive open-chain tetrapyrrole chromophore of phycocyanin (PC), chromoprotein derived from the cyanobacterium Arthrospira platensis, can bind a plethora of different proteins, both in a noncovalent and covalent manner. This study aimed to investigate interactions of PCB with S protein and RBD respectively. Electrophoretic techniques, fluorescence spectroscopy, and inhibition of S–PCB and RBD–PCB covalent adduct formation using iodoacetamide and N-ethylmaleimide, were employed to examine interactions of PCB with S protein and RBD, while the effects of PCB binding on RBD structure were studied by CD spectroscopy. SDS-PAGE with Zn2+ staining has revealed that PCB covalently binds to both S protein and RBD, via free cysteine residues. Binding constants determined by the fluorescence quenching method were: 2.1×107 M–1 for PCB and S protein and 8.4×104 M–1 for PCB and RBD. Far-UV circular dichroism spectra showed that the binding of PCB influences RBD structure by decreasing the disordered structure content. Due to moderately strong noncovalent interactions of PCB with S protein and RBD, as well as covalent adducts formation, it may exert one of its many bioactive effects via impact on S protein binding to ACE2 receptor.

The prevalence of microplastics (MP) pollution in different zones of the environment has been established by several studies [1]. Due to its widespread presence, MP have found its way into food items. Fish, shellfish, water, milk, salt, and sugar are just some examples of the food we commonly consume that are contaminated with MP [2]. Human ingestion of MP is already well-established but there is limited data regarding how MP affect human gastric digestion of food components, especially proteins. In this study, we investigated the effects of polystyrene (PS) MP on pepsin, the major protease in human gastric digestion. Pepsin activity was tested during exposure to two different sizes -10 μm (PS10) and 100 μm (PS100), and three different quantities- low count (142 particles), moderate count (1420 particles), and high count (14200 particles), of PS using haemoglobin as substrate. Results showed that exposure to PS100 has no effect on enzyme activity. However, exposure to high count PS10 considerably reduced pepsin activity from 2957 ± 310 U/mg to 1674 ± 270 U/mg. To test the effect on food digestion, high count PS10 was added to a sample of commercially available liquid bovine milk (defatted). In this case, the static in vitro simulation of gastric digestion was followed to mimic human digestion of food [3]. Milk digesta at different time points (5, 10, 15, 20, 30, 60, 90, 120 minutes) were obtained to monitor the progress of protein degradation. SDS-PAGE showed no difference in the peptide bands from 30-120 minutes. However, bands corresponding to caseins were not observed at 5 minutes when PS10 was present. Additionally, 14 kDa fragments were not observed at 10-20 minutes. Washing of the PS particles followed by SDSPAGE revealed a faint pepsin band from all time points. At 5 and 10 minutes, faint peptide bands >10kDa were also observed. These suggest that pepsin and some milk peptides were adsorbed on the surface of PS10. Zeta potential analysis of PS revealed a slightly negative surface charge which could explain the adsorption and disappearance of peptide bands. This adsorption of pepsin on PS did not seem to affect its overall protease activity. However, the interaction of milk peptides with PS may reduce the nutrients human could acquire from milk. Acknowledgements This study was supported by Ghent University Global Campus; Special Research Fund (BOF) of Ghent University (grant number 01N01718) and IMPTOX European Union’s Horizon 2020 research and innovation program (grant number 965173). References [1] S. Sharma, S. Basu, N. P. Shetti, M. N. Nadagouda, T. M. Aminabhavi (2021) Chem. Eng. J., 408, 127317. [2] K. D. Cox, G. A. Covernton, H. L. Davies, J. F. Dower, F. Juanes, S. E. Dudas (2019) Environ. Sci. Technol., 53(12), 7068–7074. [3] A. Brodkorb et al. (2019) Nat. Protoc., 14(4), 991– 1014.