Introduction
Phoenix is an immortal bird that cyclically regenerates. Like a phoenix, SARS-CoV-2 has cyclically regenerated several dozen times through mutations from Hu-1 to the newest Omicron BA.2.86 Pirola variant. With every new mutation and new variant, SARS-CoV-2 has obtained a new life appearing slightly different from its predecessor. Some of the variants have caused pandemic waves of high amplitude [Campi et al., 2022; Dutta, 2022; Nasir et al., 2023; Thakur et al., 2022; Amin et al., 2022]. Differently from the mythological phoenix, the SARS-CoV-2 phoenix has disappeared and reborn in front of our eyes during the three years of the pandemic. Thus, SARS-CoV-2 has appeared in late-2019 in Wuhan and was labeled as the Hu-1 wild type [Holmes et al., 2021; Hu et al., 2021; WHO, 2021; Andersen et al., 2020; Chan et al., 2020]. Mutations have occurred mostly in the part of the genome that encodes the spike glycoprotein [Magazine et al., 2022; Souza et al., 2022; Kumar et al., 2023; Harvey et al., 2021; Rahbar et al., 2021; Gobeil et al., 2021]. However, mutations have occurred in other viral proteins as well [Senthilazhagan et al., 2023; Ichikawa et al., 2022]. Evolution of viruses and formation of new variants has been described in the literature [ECDC, 2023a; CDC, 2023b; WHO, 2023b; Aleem et al., 2023; NCBI, 2023a; Carabelli et al., 2023; Chen et al., 2022; Rahman et al., 2022; Dubey et al., 2021; Singh et al., 2022; Ramesh et al., 2021; Popovic, 2023a, 2022b; Popovic et al., 2023a, 2023b].
BA.2.86 Pirola is the latest variant of SARS-CoV-2, which is characterized by many mutations [CDC, 2023a]. The number of mutations in BA.2.86 variant compared to the XBB.1.5 variant is similar to the difference between the first Omicron variant and its predecessor Delta variant [CDC, 2023a]. This might give the BA.2.86 variant the ability to infect people who have previously had COVID-19 or who have received COVID-19 vaccines [CDC, 2023a], which has raised concerns in the public [EuroNews, 2023; CNBC, 2023]. Globally, as of 30 August 2023, there have been 770,085,713 confirmed cases of COVID-19, including 6,956,173 deaths [WHO, 2023a]. Even though there has been a decrease in number of daily infections worldwide since late 2022, with the appearance of the new Omicron BA.2.86 variant, the number of COVID-19 cases has increased since the mid-2023. Due to this situation, it would be good to perform a physicochemical analysis of the BA.2.86 variant to compare its ability to infect host cells with that of the previous variants of SARS-CoV-2.
SARS-CoV-2 belongs to the Coronaviridae family [Coronaviridae Study Group of the International Committee on Taxonomy of Viruses, 2020; Yang et al., 2020; Rajagopalan, 2021; Abdelrahman et al., 2020; Zhu et al., 2020]. It is an enveloped virus, with a single stranded positive sense RNA genome [Bartas et al., 2022; Alexandersen et al., 2020; Cao et al., 2021; Brant et al., 2021; Lee et al., 2022; Chai et al., 2021]. SARS-CoV-2 virus particles contain four kinds of structural proteins: nucleocapsid (N), membrane (M), envelope (E) and spike (S) [Troyano-Hernáez et al., 2021; Satarker and Nampoothiri, 2020; Jackson et al., 2022; Schoeman and Fielding, 2019; Dolan et al., 2022; Yao et al., 2020]. The nucleocapsid protein binds to the viral RNA and forms the nucleocapsid [Wu et al., 2023, 2021; Cubuk et al., 2021; Perdikari et al., 2020; Jack et al., 2021; Wang et al., 2022]. The nucleocapsid is enclosed in a lipid bilayer envelope that contains membrane and envelope proteins [Kumar and Saxena, 2021; Ke et al., 2020; Hardenbrook and Zhang, 2022; Motsa and Stahelin, 2021; Mesquita et al., 2021; Mandala et al., 2020]. The spike proteins point out from the surface of the virus particle [Taha et al., 2023; Huang et al., 2020; Kordyukova et al., 2023; Chen et al., 2021; Zeng et al., 2021; Almehdi et al., 2021]. They represent the virus antigens that bind to host cell receptors [Gale, 2022; Popovic, 2023b, 2023c, 2023d; Popovic and Popovic, 2022].
SARS-CoV-2 belongs to RNA viruses [V’kovski et al., 2021; Khan et al., 2021; Zhang et al., 2021]. RNA viruses exhibit a great tendency to mutate [Duffy, 2018; Villa et al., 2021; Drake and Holland, 1999; Sanjuán and Domingo-Calap, 2016; Domingo et al., 2021; Elena et al., 2000; Dolan et al., 2018; Schulte et al., 2015; Popovic, 2022c]. Mutations lead to change in information content of the viral genome, chemical changes in elemental composition, as well as thermodynamic properties (enthalpy, entropy and Gibbs energy of formation and biosynthesis) [Popovic, 2022d, 2022e, 2022f]. Mutation as a biological phenomenon, except through sequencing, can be detected through the atom counting method, which allows detection of changes in elemental composition that appear as a consequence of mutations [Popovic, 2022g]. Furthermore, changes in elemental composition lead to changes in thermodynamic properties [Battley, 2013, 1999a, 1998; Battley and Stone, 2000; Patel and Erickson, 1981; Ozilgen and Sorgüven, 2017; Hurst and Harrison, 1992; Popovic, 2019; Popovic et al., 2021].
Since 2019, in the literature, elemental composition and thermodynamic properties have been reported for several virus species: Ebola [Popovic, 2022h], Monkeypox [Popovic, 2022a], SARS-CoV-2 [Şimşek et al., 2021; Degueldre, 2021; Gale, 2022; Popovic and Popovic, 2022; Popovic, 2022e, 2022d; Popovic et al., 2023a, 2023b; Popovic and Minceva, 2020b], MERS-CoV [Popovic and Minceva, 2020b], SARS-CoV [Popovic and Minceva, 2020b], HIV [Gale, 2020], arboviruses [Gale, 2020, 2019, 2018] and bacteriophages [Maskow et al., 2010; Guosheng et al., 2003; Popovic, 2023e]. Biothermodynamic mechanisms that influence infectivity and pathogenicity of different variants and the consequences on epidemiology and mechanisms of spreading of SARS-CoV-2 are available in the literature [Lucia et al., 2021, 2020a, 2020b; Kaniadakis et al., 2020; Head et al., 2022; Özilgen and Yilmaz, 2021; Pateras et al., 2022; Yilmaz et al., 2020; Trancossi et al., 2021].
The aim of this paper is to explore changes in empirical formula, molar mass, biosynthesis reactions, and thermodynamic properties (enthalpy, entropy, Gibbs energy) of formation and biosynthesis of the BA.2.86 Pirola variant. Based on the obtained results, the goal is to perform an assessment of the risk of spreading of an epidemic/pandemic of the BA.2.86 variant in late 2023. Moreover, the pathogenicity of the BA.2.86 variant will be compared to those of the earlier variants of SARS-CoV-2.
Methods
Data sources
The genetic sequence of the Omicron BA.2.86 Pirola variant of SARS-CoV-2 was taken from GISAID, the global data science initiative [Khare et al., 2021; Elbe and Buckland-Merrett, 2017; Shu and McCauley, 2017]. It can be found under the accession number EPI_ISL_18138566 and is labeled hCoV-19/USA/OH-ODH-SC3032044/2023. It was isolated on July 29, 2023 in Cuyahoga County, Ohio. Thus, the findings of this study are based on metadata associated with one sequence available on GISAID up to September 24, 2023, and accessible at
https://doi.org/10.55876/gis8.230924yd (please see the Supplementary Material for more details).
The sequence of the nucleocapsid phosphoprotein of SARS-CoV-2 was obtained from the NCBI database [Sayers et al., 2022; NCBI, 2023b], under the accession number QIK50455.1 [NCBI, 2023c]. The sequence of the membrane protein of SARS-CoV-2 was obtained from the NCBI database [Sayers et al., 2022; NCBI, 2023a], under the accession number QHR63293.1 [NCBI, 2023d]. The sequence of the spike glycoprotein of SARS-CoV-2 was obtained from the NCBI database [Sayers et al., 2022; NCBI, 2023a], under the accession number QHR63290.2 [NCBI, 2023e]. The number of protein copies in the virus particle was taken from [Neuman and Buchmeier, 2016; Neuman et al., 2011; Neuman et al., 2006]. In a SARS-CoV-2 particle, there are 2368 copies of the nucleocapsid phosphoprotein, 1184 copies of the membrane protein and 222 copies of the spike glycoprotein [Neuman and Buchmeier, 2016; Neuman et al., 2011; Neuman et al., 2006].
Empirical formulas
The empirical formulas and molar masses of the virus particle and nucleocapsid of the Omicron BA.2.86 Pirola variant of SARS-CoV-2 were determined through the atom counting method [Popovic, 2022g]. They were determined based on the genetic sequence, protein sequences and virus morphology.
The atom counting method is a computational approach for determination of empirical formulas, chemical formulas and molar masses of macromolecules and macromolecular assemblies [Popovic, 2022g; Popovic et al., 2023c]. The atom counting method can analyze a wide range of macromolecules, including be double-stranded DNA, single-stranded DNA, single-stranded RNA, double-stranded RNA, proteins, polypeptides, oligopeptides etc. [Popovic, 2022g; Popovic et al., 2023c]. Furthermore, the atom counting method can be used to analyze macromolecular assemblies, such as virus particles, virus nucleocapsids, protein complexes, complexes of nucleic acids and proteins etc. [Popovic, 2022g; Popovic et al., 2023c].
The atom counting method is implemented with a computer program [Popovic, 2022g]. The input of the program are genetic sequences, protein sequences and morphological data [Popovic, 2022g]. The morphological data include protein copy numbers in macromolecular assemblies, size of the macromolecular assembly, whether the macromolecular assembly possesses lipids and carbohydrates etc. [Popovic, 2022g]. The output of the atom counting method are chemical formulas of macromolecules, empirical formulas of macromolecules, chemical formulas of macromolecular assemblies, empirical formulas of macromolecular assemblies, molar masses of empirical formulas of macromolecules, molar masses of empirical formulas of macromolecular assemblies, molar masses of macromolecules and molar masses of macromolecular assemblies [Popovic, 2022g].
The program that implements the atom counting method goes along the sequences of macromolecules (e.g. nucleic acids or proteins), which consist of residues [Popovic, 2022g]. Every residue has a well-defined chemical formula [Popovic, 2022g]. Thus, the program adds the atoms of different elements that come from every residue [Popovic, 2022g]. This gives the chemical formula of the macromolecule [Popovic, 2022g]. In case of macromolecular assemblies, the numbers of atoms of different elements are multiplied by the numbers of copies of the macromolecule in the macromolecular assembly [Popovic, 2022g]. If a macromolecular assembly contains lipids, the atoms coming from lipids are taken into account based on morphological data [Popovic, 2022g]. Then atoms coming from all the macromolecules are added to find the numbers of atoms of different elements in the macromolecular assembly [Popovic, 2022g]. These are used to find the empirical formula through the equation
where
nJ is the number of atoms of element
J in the empirical formula,
NJ is the total number of atoms of element
J in the molecule or macromolecular assembly, and
NC is the total number of carbon atoms in the molecule or macromolecular assembly [Popovic, 2022g].
Thermodynamic properties of live matter
Thermodynamic properties of virus particle and nucleocapsid of the Omicron BA.2.86 variant were determined with the Patel-Erickson model [Patel and Erickson, 1981; Battley, 1998] and Battley model [Battley, 1999a; Battley and Stone, 2000]. They were determined based on empirical formulas. The Patel-Erickson model was used to find enthalpy [Patel and Erickson, 1981; Battley, 1998] and the Battley model was used to find entropy [Battley, 1999a; Battley and Stone, 2000], which were then combined to find Gibbs energy.
To find enthalpy of live matter (i.e. virus particle or nucleocapsid) with the Patel-Erickson model, the empirical formula is used to find the number of electrons transferred to oxygen during complete oxidation,
E, with the equation [Patel and Erickson, 1981; Battley, 1998]
E is then used to find standard enthalpy of combustion of live matter, Δ
CH⁰, with the equation
The Patel-Erickson model is based on Thornton’s theory of combustion, sometimes called Thornton’s rule [Thornton, 1917]. Thornton’s rule states that the process that releases energy during combustion is acceptance of electrons by oxygen which is highly electronegative [Thornton, 1917]. Δ
CH⁰ is then used to calculate standard enthalpy of formation of live matter, Δ
fH⁰, with the equation [Battley, 1998, 1999b, 1992]
Entropy of live matter is calculated with the Battley model, based on its elemental composition. Standard molar entropy of live matter,
S⁰m, is given by the equation
where
S⁰m(
J) is standard molar entropy of element
J,
aJ number of atoms of element
J in its standard state elemental form, and
nJ the number of atoms of element
J in the empirical formula of live matter [Battley, 1999a; Battley and Stone, 2000]. The summation is over all elements
J of which the live matter consists [Battley, 1999a; Battley and Stone, 2000]. The changed environment of the atoms of elements in live matter is taken into account by the constant 0.187. The Battley model can also be used to find standard entropy of formation of live matter, Δ
fS⁰, if the constant 0.187 is changed to -0.813 [Battley, 1999a; Battley and Stone, 2000]
Finally, Δ
fS⁰ and Δ
fH⁰ are combined to find standard Gibbs energy of formation, Δ
fG⁰, of live matter
where
T is temperature [Atkins and de Paula, 2011, 2014].
Biosynthesis reactions
Biosynthesis reactions of the virus particle and nucleocapsid of the Omicron BA.2.86 variant were formulated based on their empirical formulas. Biosynthesis reactions are macrochemical equations of conversion of nutrients into new live matter in metabolism [Assael et al., 2022; von Stockar, 2013a, 2013b; Battley, 2013, 1999b]. The general biosynthesis reaction for viruses has the form
where (Amino acid) represents a mixture of amino acids, which has the empirical formula CH
1.798O
0.4831N
0.2247S
0.022472 [Popovic et al., 2023a, 2023b; Popovic, 2023a, 2023b, 2022c]. Newly synthetized live matter, (Bio), is represented with its empirical formula [Popovic et al., 2023a, 2023b; Popovic, 2023a, 2023b, 2022c]. The source of energy, carbon, nitrogen and sulfur for biosynthesis are the amino acids [Popovic et al., 2023a, 2023b; Popovic, 2023a, 2023b, 2022c]. The electron acceptor is O
2 [Popovic et al., 2023a, 2023b; Popovic, 2023a, 2023b, 2022c; Annamalai, 2021]. The source of phosphorus is HPO
42- [Popovic et al., 2023a, 2023b; Popovic, 2023a, 2023b, 2022c]. Excess H
+ ions generated during biosynthesis are absorbed by the HCO
3- ion, which is a part of the bicarbonate buffer [Popovic et al., 2023a, 2023b; Popovic, 2023a, 2023b, 2022c]. Excess sulfur atoms are released in the form of the SO
42- ion, which is an additional metabolic product [Popovic et al., 2023a, 2023b; Popovic, 2023a, 2023b, 2022c]. The oxidized carbon atoms are released in the form of H
2CO
3, which is also a part of the bicarbonate buffer [Popovic et al., 2023a, 2023b; Popovic, 2023a, 2023b, 2022c].
Thermodynamic properties of biosynthesis
Thermodynamic properties of biosynthesis of the virus particle and nucleocapsid of the Omicron BA.2.86 variant of SARS-CoV-2 were calculated with the Hess’s law. They were found based on the biosynthesis reactions and thermodynamic properties of live matter. Thermodynamic properties of biosynthesis include standard enthalpy of biosynthesis, Δ
bsH⁰, standard entropy of biosynthesis, Δ
bsS⁰, and standard Gibbs energy of biosynthesis, Δ
bsG⁰ [von Stockar, 2013a, 2013b]. They can be found by application of the Hess’s law to the biosynthesis reactions
where
ν represents a stoichiometric coefficient [Popovic et al., 2023a, 2023b; Popovic, 2023a, 2023b, 2022c; Atkins and de Paula, 2011, 2014; von Stockar, 2013b; Battley, 1998]. Of particular importance among these properties is Δ
bsG⁰, since it represents the physical driving force for the process of multiplication of microorganisms [von Stockar, 2013a, 2013b; von Stockar and Liu, 1999], including viruses [Popovic et al., 2023a, 2023b; Popovic, 2023a, 2023b, 2022c].
Results
Empirical formulas and molar masses were determined for the first time for the virus particle and nucleocapsid of the Omicron BA.2.86 Pirola variant of SARS-CoV-2. They are shown in
Table 1. The empirical formulas were determined through the atom counting method [Popovic, 2022g], based on the genetic sequence, protein sequences and morphology of the virus. The empirical formula of the virus particle of the Omicron BA.2.86 variant is CH
1.639023O
0.284130N
0.230031P
0.006440S
0.003765 and has a molar mass of 21.75 g/C-mol. The molar mass of the entire virus particle of the Omicron BA.2.86 variant is 219.7 MDa. The empirical formula of the nucleocapsid of the Omicron BA.2.86 variant is CH
1.570946O
0.343118N
0.312432P
0.006007S
0.003349 and has a molar mass of 23.75 g/C-mol. The molar mass of the entire nucleocapsid of the Omicron BA.2.86 variant is 117.6 MDa.
Table 2 shows thermodynamic properties of the virus particle and nucleocapsid of the Omicron BA.2.86 variant. They were determined through the Patel-Ericson model [Patel and Erickson, 1981; Battley, 1998] and Battley model [Battley, 1999a; Battley and Stone, 2000], based on the empirical formulas (
Table 1). They include standard enthalpy of formation, Δ
fH⁰, standard molar entropy,
Sm⁰, and standard Gibbs energy of formation, Δ
fG⁰. For the virus particle of the Omicron BA.2.86 variant, standard enthalpy of formation is -64.43 kJ/C-mol, standard molar entropy is 30.70 J/C-mol K and standard Gibbs energy of formation is -24.64 kJ/C-mol. For the nucleocapsid of the Omicron BA.2.86 variant, standard enthalpy of formation is -75.41 kJ/C-mol, standard molar entropy is 32.47 J/C-mol K and standard Gibbs energy of formation is -33.32 kJ/C-mol.
Table 3 shows the biosynthesis stoichiometry of the virus particle and nucleocapsid of the Omicron BA.2.86 variant. They were formulated based on the empirical formulas (
Table 1). The general biosynthesis reaction has the form (Amino acid) + CH
2O + O
2 + HPO
42- + HCO
3- → (Bio) + SO
22- + H
2O + H
2CO
3, where (Amino acid) represents a mixture of amino acids with the formula CH
1.798O
0.4831N
0.2247S
0.022472 and (Bio) represents the empirical formula of live matter.
Table 4 gives thermodynamic properties of biosynthesis of the virus particle and nucleocapsid of the Omicron BA.2.86 variant of SARS-CoV-2. They were calculated with the Hess’s law [Atkins and de Paula, 2011, 2014; von Stockar, 2013a, 2013b], based on the biosynthesis stoichiometry (
Table 3) and thermodynamic properties of live matter (
Table 2). They include standard enthalpy of biosynthesis, Δ
bsH⁰, standard entropy of biosynthesis, Δ
bsS⁰, and standard Gibbs energy of biosynthesis, Δ
bsG⁰. For the virus particle of the Omicron BA.2.86 variant, standard enthalpy of biosynthesis is -4.80 kJ/C-mol, standard entropy of biosynthesis is 6.94 J/C-mol K and standard Gibbs energy of biosynthesis is -6.94 kJ/C-mol. For the nucleocapsid of the Omicron BA.2.86 variant, standard enthalpy of biosynthesis is -232.88 kJ/C-mol, standard entropy of biosynthesis is -37.48 J/C-mol K and standard Gibbs energy of biosynthesis is -221.75 kJ/C-mol.