Molecular mimicry of the receptor-binding domain of the SARS-CoV-2 spike protein: from the interaction of spike-specific antibodies with transferrin and lactoferrin to the antiviral effects of human recombinant lactoferrin

The pathogenesis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection involves dysregulations of iron metabolism, and although the mechanism of this pathology is not yet fully understood, correction of iron metabolism pathways seems a promising pharmacological target. The previously observed effect of inhibiting SARS-CoV-2 infection by ferristatin II, an inducer of transferrin receptor 1 (TfR1) degradation, prompted the study of competition between Spike protein and TfR1 ligands, especially lactoferrin (Lf) and transferrin (Tf). We hypothesized molecular mimicry of Spike protein as cross-reactivity of Spike-specific antibodies with Tf and Lf. Thus, strong positive correlations (R² > 0.95) were found between the level of Spike-specific IgG antibodies present in serum samples of COVID-19-recovered and Sputnik V-vaccinated individuals and their Tf-binding activity assayed with peroxidase-labeled anti-Tf. In addition, we observed cross-reactivity of Lf-specific murine monoclonal antibody (mAb) towards the SARS-CoV-2 Spike protein. On the other hand, the interaction of mAbs produced to the receptor-binding domain (RBD) of the Spike protein with recombinant RBD protein was disrupted by Tf, Lf, soluble TfR1, anti-TfR1 aptamer, as well as by peptides RGD and GHAIYPRH. Furthermore, direct interaction of RBD protein with Lf, but not Tf, was observed, with affinity of binding estimated by K_D to be 23 nM and 16 nM for apo-Lf and holo-Lf, respectively. Treatment of Vero E6 cells with apo-Lf and holo-Lf (1–4 mg/mL) significantly inhibited SARS-CoV-2 replication of both Wuhan and Delta lineages. Protective effects of Lf on different arms of SARS-CoV-2-induced pathogenesis and possible consequences of cross-reactivity of Spike-specific antibodies are discussed.

[INTERACTION OF THE DYE CONGO RED WITH FIBRILS OF LYSOZYME, BETA2-MICROGLOBULIN AND TRANSTHYRETIN]

By means of spectrophotometric assay we investigated interaction of the dye Congo red (CR) with fibrils of model proteins--hen egg white lysozyme, recombinant human beta2-microglobulin (b2M) and recombinant human transthyretin (TTR). The commercial dye sample was found to contain a significant amount of impurities. Methods for the dye purification are disclosed and CR molar extinction coefficient at 490 nm (ε490) was determined to be 3.3 x 10(4) M(-1) x cm(-1) at pH above 6.0. Formation of the CR-fibril complex results in changes in the dye visible absorption spectrum. According to the data on titration of fibril solutions with excess of the dye, CR binds to lysozyme fibrils at a ratio of about 5 molecules per protein monomer within fibril structure, to b2M fibrils--about 4 molecules per monomer, to TTR fibrils--about 4 molecules per subunit of the protein.

CHARACTERISTICS OF AMYLOID DEPOSITS DETECTED IN THE INTERNAL ORGANS OF mdx MICE

The dystrophin-deficient mdx mouse is the most commonly used experimental model of Duchenne muscular dystrophy (DMD). Although the amyloid has been shown in the muscle biopsies of patients with different types of muscular dystrophies, there are no data on the amyloid accumulations in the biopsy of DMD patients or mdx mouse. Therefore, the aim of the present study was to testify the hypothesis of probable accumulation of amyloid in the visceral organs of mdx mouse. Specimens of myocardium, kidneys, and liver of male and female mdx mice aged from 2 months to 1.5 years (n = 9) were used in the study. The histochemical staining with Congo red demonstrated amyloid accumulations in the studied organs of the mdx mice. Morphology and localization of the found accumulations were described in details and analyzed. The mass-spectrometric study determined the vitronectin and apolipoprotein A-II as the most probable components of the amyloid accumulations in the mdx mouse.

"Finnish" mutations in LDL receptor gene: a rare cause of familial hypercholesterolemia in St. Petersburg and Petrozavodsk

The search for two mutations, FH-Helsinki and FH-North Karelia, in LDL receptor gene was carried out in patients with familial hypercholesterolemia from St. Petersburg (80 families) and Petrozavodsk (80 families) using allele-specific PCR and analysis of single-stranded DNA fragment conformation polymorphism (SSCP analysis) with subsequent sequencing. The FH-North Karelia mutation was found in one family in St. Petersburg and in one family in Petrozavodsk, while FH-Helsinki mutation was not detected in any of the samples. Hence, the two "Finnish" mutations together responsible for 2/3 familial hypercholesterolemia cases in Finland were extremely rare in the Russian regions neighboring Finland.

[THE INFLUENCE OF THE PREPARATION PRETREATMENT ON IN SITU DETECTION OF 5-METHYLCYTOSINE IN METAPHASE CHROMOSOMES AND IN INTERPHASE NUCLEI]

Qualitative and quantitate analysis of DNA methylation in situ at the level of cells, chromosomes and chromosomal domains is extremely important for the diagnosis and treatment of various diseases, the study of ageing and the consequences of environmental impacts. An important question arises, whether the revealed in situ methylation pattern reflects DNA methylation per se and (or) availability of the DNA for antibodies, which in turn depends on the peculiarities of chromatin structure and chromosome condensation. These events can lead to an incorrect evaluation of the actual pattern of DNA methylation. To avoid this shortcoming as far as possible, we have modified the most widely used method of revealing 5-methylcytosine in situ with monoclonal antibodies. Here we have shown that the detection of DNA methylation staining of chromosomes including C-heterochromatin, chromosomal arms and sister chromatids is drastically dependent on pretreatment of chromosomal preparations for immunocytochemical study using fluorescent antibodies. Using undifferentiated stem cells of mouse embryonal carcinoma line F9, it has been found that change in preparations storage results in a sharp fluorescence decrease up to complete disappearance of the signal in centromeric heterochromatin. With the help of the method described in the work, we have first revealed the asymmetry of sister chromatids methylation in metaphase chromosomes of F9 cell and lymphocytes of human periphery blood. This may lead to asymmetry of transcriptional signature of daughter cells after division. The proposed here modification of 5-methylcytosine detection in situ provides a more complete characterization of methylation of chromosomes and chromosomal domains, compared to previously published methods.

[New mutations in low-density lipoprotein receptor gene in familial hypercholesterolemia patients from Petrozavodsk]

Using an automated fluorescent single-strand conformation polymorphism (SSCP) analysis of the entire coding region, promoter zone, and exon-intron junctions of the low-density lipoprotein (LDL) receptor gene, we examined 80 DNA samples of patients with familial hypercholesterolemia (FH) from Petrozavodsk. We revealed mutations that might cause FH in five probands, including FH-North Karelia (c.925-931del7) mutation and four previously unknown mutations. These novel mutations included a transversion (c.618T>G (p.S206R), one nucleotide insertion c.195_196insT (p.FsV66:D129X), a complex gene rearrangement c.192del10/ins8 (p.FsS65:D129X), and a single nucleotide deletion c.2191delG (p.FsV731:V736X). Three out of four novel mutations produce an open reading frame shift and the premature termination of translation. An analysis of the cDNA sequence of the LDL receptor showed that this might result in the formation of a transmembrane-domain-deficient receptor that is unable to bind and internalize the ligand. Our results suggest the absence of a strong founder effect associated with FH in the Petrozavodsk population.

[Comparative aspects of structural organization of astrocytes of the first layer of the human and rat cerebral cortex]

Importance of study of astrocytes for fundamental biology and medicine is due their key role in formation of the brain barrier system. On taking into consideration the controversial data on structure of the mammalian neocortex superficial layers, of great actuality are the comparative studies of the structural and cytochemical organization of astrocytes in human and in the laboratory animals used in the experimental studies connected with modeling of brain diseases and traumas. The goal of the present work was to study structural organization of astrocytes in the human and rat neocortical layer I. The work was on the autopsy and experimental material from Wistar rats. Astrocytes were revealed immunocytochemically by using antibodies to GFAP, vimentin and nestin. The preparations were examined with aid of light and confocal laser microscopy. No significant difference in the sizes of perinuclear areas were established between the rat and human astrocytes. In the majority of cortex regions, the specter of proteins forming intermediate filaments in these cells was identical. However, there were essential differences revealed in organization of the superficial glial bordering lamina (SGBL). The human SGBL is formed by interlacing of thin processes in the layer I processes, whereas the rat SGBL is represented by specialized astrocytes spread along the cortical surface and connected with the wide-blade processes. The human layer I astrocytes have translaminar processes passing via several cortical layers, whereas in rats such processes are located within the limits of one layer. The revealed differences in the astrocyte structural organization should be taken into account when interpreting results of experimental studies carried out on rats and extrapolating these results to human.

Expression in E. coli and purification of the fibrillogenic fusion proteins TTR-sfGFP and β2M-sfGFP

The possibility of obtaining recombinant fibrillogenic fusion proteins such as transthyretin (TTR) and β2-microglobulin (β2M) with a superfolder green fluorescent protein (sfGFP) was studied. According to the literature data, sfGFP is resistant to denaturating influences, does not aggregate during renaturation, possesses improved kinetic characteristics of folding, and folds well when fused to different polypeptides. The corresponding DNA constructs for expression in Escherichia coli were created. It could be shown that during expression of these constructs in E. coli, soluble forms of the fusion proteins are synthesized. Efficient isolation of the fusion proteins was performed with the help of nickel-affinity chromatography. For this purpose a polyhistidine sequence (6-His-tag) was incorporated into the C-terminus of the sfGFP. We could show that the purified fusion proteins contained full-size sequences of the most amyloidogenic TTR variant, TTR(L55P) and β2M, and also sfGFP possessing fluorescent properties. In the course of fibrillogenesis both fusion proteins demonstrated their ability to form fibrils that were clearly detectable by atomic force microscopy. Furthermore, with the help of confocal microscopy we were able to reveal structures (exhibiting fluorescence) that are formed during fibrillogenesis. Thus, the use of sfGFP has made it possible to avoid formation of inclusion bodies (IB) during the synthesis of recombinant fusion proteins and to obtain soluble forms of TTR(L55P) and β2M that are suitable for further studies.

[Transthyretin gene V30M, H90N, and del9 mutations in cardiomyopathy patients from St. Petersburg]

A search of transthyretin (TTP) gene mutations was conducted in patients with cardiomyopathies from St. Petersburg. Mutations H90N, V30M, G47A, and deletion (del9) of nucleotides GACTTCTCC in position 6776 from the start codon of the TTP gene (in position 98782 according to reference sequence AC079096 (NCBI) was found. The H90N mutation in the third exon of TTP gene was detected in a son of a cardiomyopathy patient and in his mother, which lacked any clinical manifestations. Mutations V30M and G47A in exon 2 of TTP gene were found in heterozygous and homozygous state, respectively, in one of the probands. Deletion (del9) was revealed in a patient with cardiomyopathy and in his two daughters from different marriages, who had no clinical manifestations of the disease. All the mutations revealed in this study were previously identified in other populations.

[Structural organization of superficial glial limiting membrane and layer I astrocytes in rat brain cortex]

A study of structural and functional organization of the boundaries separating CNS compartments is a fundamental task of neurobiology. Taking into account the contradictory data on the structure of superficial layers of mammalian neocortex, it is pertinent to study structural and cytochemical organization of astrocytes--the main components of the brain barrier system in animals that are often used for experimental modeling of brain diseases and injuries. The aim of the present work was to study the structural organization of layer I astrocytes of rat neocortex. Astrocytes were demonstrated immunocytochemically using anti-GFAP, anti-vimentin and anti-nestin antibodies using light and confocal laser microscopy. The results of the study demonstrated that the superficial glial limiting membrane had significant structural differences in different cortical regions. Astrocytes in layer I of rat neocortex were different from typical protoplasmic astrocytes, common to gray matter The regional peculiar features of superficial glial limiting membrane organization that were found in this study, are probably determined by the differences in functional characteristics of CSF-encephalic barrier in the specific regions of the brain.

[Human intra-intronic minisatellite UPS29 associated with neurological diseases regulates reporter gene EGFP expression depending on cell type]

Earlier, it was established that polymorphism of minisatellite UPS29 located in one of introns of human gene CENTB5 (ACAP3) was associated with Parkinson's disease and epilepsy. The main aim of this work was to elucidate if that minisatellite could regulate reporter gene activity, and if such activity was tissue (cell)-specific. To this end there was used transient transfection of HeLa cells, mouse embryonal carcinoma line F9, and rat astrocytes cultures with plasmides which contained reporter gene EGFP under eukaryotic promoter ROSA26 and different allelles of minisatellite UPS29. It was found that UPS29 possessed enhancer-like activity in neuronal type cells.

[Genetic variants of CYP1B1 and WDR36 in the patients with primary congenital glaucoma and primary open angle glaucoma from Saint-Petersburg]

In 32 patients with primary congenital glaucoma (PCG), a search for mutations in the myocilin (MYOC), cytochrome P450B1 (CYP1B1), and WDR36 genes was performed. The Q368X mutation in myocilin gene, typical of the patients with adult-onset primary open-angle glaucoma (POAG), was not detected in the PCG patients. Screening of the CYP1B1 introns 2 and 3 for the presence of mutations in PCG patients revealed only six DNA polymorphisms, including IVS1-12ntT>C (g.3793 T>C), A119S (g.4160 G>T; GCC>TCC), G188G (g.4369 C>A; GGC>GGA), L432V (G.8131 C>G; CTG>GTG), D449D (g.8184 C>T; GAC>GAT), and N453S (g.8195 A>G; AAC>AGC) (nucleotide numbering is given in accordance with the GenBank sequence U56438). In the groups of PCG patients and donors without eye diseases, the frequencies of these variants were not statistically significantly different, pointing to the neutrality of these polymorphisms. Furthermore, the CYP1B1 polymorphism L432V, considered to be associated with POAG in some world populations, was not associated with this disease in the patients from St. Petersburg. DNA collections obtained from the POAG and PCG patients and from the control group were tested for the carriage of the worldwide distributed mutations of the WRD36 gene, D658G, R529Q, A449T, and N355S. D658G variant was found with equally low frequencies in the groups of POAG and PCG patients, as well as in the control group. Mutations A449T and R529Q were found only once each, while mutation N355S was not detected in any of the groups examined. Our results indicate that the WDR36 variants make no substantial contribution to the development of POAG and PCG in the patients from St. Petersburg and represent normal DNA polymorphism. It is likely that in most of the PCG patients from the population examined the disease is not associated with the CYP1B1 gene defects.

[The study of cerebral astrocyte spatial organization using confocal laser microscopy]

Three-dimensional reconstruction of cytoarchitectonic relations of the main components of the nervous tissue appears to be an important, yet an extremely laborious task of neuromorphology. The aims of the present study were: to develop the method permitting accurate visualization of astrocytes in rat brain slices thicker then 30 microm, to create an adequate algorithm for the study of the slides received using a confocal microscope and to perform the three-dimensional reconstructions of astrocytes from Z-series of confocal images. Different variants of slide preparation (various clearing reagents, fluorochromes, mounting media) were investigated, together with the operating modes of confocal microscope, methods of digital image processing etc. The methodical approaches are recommended that may be successfully applied for three-dimensional reconstruction and detection of spatial relations of astrocytes in mammalian brain.

[Novel BRCA1 gene mutations in breast cancer patients from St. Petersburg]

Screening of patients with familial breast cancer from St. Petersburg for BRCA1 gene mutations resulted in identification of three mutations (414del3, 276delA, and A622V) and two polymorphisms (P871L and S1436S). Mutations 4146del3 and 276delA are novel, never previously described elsewhere. Deletion 2761delA produces a reading frame shift, premature protein synthesis termination and can cause predisposition for breast cancer. Deletion 414de13 does not cause a frame shift, but can result both in the disappearance of amino acid residue (D1343del) in the BRCA1 protein and in alteration of folding of the protein, entailing loss of its functional activity. Two variants of nucleotide sequence observed in the number of patients were classified as DNA polymorphisms (P871L and S1436S) rather than mutations as they were not tightly associated with the increased risk of breast cancer.

Atomic Force Microscopy Study of Peptides Homologous to Beta-Domain of Alpha-Lactalbumins

Symmetrical peptide GYDTQAIVENNESTEYG (WT, Wild Type) identical to 35-51 aminoacid residues of human alpha-lactalbumin (HLA) and peptide GYDTQTVVNNNGHTDYG (ID, IDeal symmetry) homologous to beta-domain of mammalian alpha-lactalbumins can form amyloid-like fibrils in conditions required for fibrillogenesis of HLA. The latter peptide can also form fibrils in deionized water. Fibrils formed by these peptides can cause forming of HLA amyloid-like aggregates in physiological conditions. These results provide an evidence for presence of amyloidogenic determinant in beta-domain of alpha-lactalbumin. Thus, symmetry in the primary structure may play the role in fibrillogenesis of proteins.

[Prevalence of widespread BRCA1 gene mutations in patients with familial breast cancer from St. Petersburg]

Ten variants different from the canonical nucleotide sequence (GenBank, U14680) has been identified when studying the mutation spectrum in gene BRCA1. Six of them (5382insC, 2963del10, 3819de15, 3875del4, 2274insA, and R1203X) cause premature termination of protein synthesis, thus predisposing to breast cancer. A missense mutation E1250K is presumed to be a factor of predisposition to cancer. We classified three variants of nucleotide sequence found in some patients as DNA polymorphisms S694S, L771L, and E1038G. The 5382insC and 3819de15 mutations have been detected in four and two families, respectively. Five of the mutations detected have not been found in Russia before. However, all mutations except for 2963del10 have been found in other populations of the world, which indicates their long evolutionary history. Two mutations found in patients from St. Petersburg (5382insC and 3875de14) have also been found in oncological patients from other regions of the Russian Federation.