The serological responses towards severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleoprotein, receptor-binding domain (RBD), and spike protein S1 are characterized by incomplete avidity maturation. Analysis with varying concentrations of urea allows to determine distinct differences in avidity maturation, though the total process remains at an unusually low level. Despite incomplete avidity maturation, this approach allows to define early and late stages of infection. It therefore can compensate for the recently described irregular kinetic patterns of immunoglobulin M and immunoglobulin G (IgG) directed towards SARS-CoV-2 antigens. The serological responses towards seasonal coronaviruses neither have a negative nor positive impact on SARS-CoV-2 serology in general. Avidity determination in combination with measurement of antibody titers and complexity of the immune response allows to clearly differentiate between IgG responses towards seasonal coronaviruses and SARS-CoV-2.Cross-reactions seem to occur with very low probability. They can be recognized by their pattern of response and through differential treatment with urea. As high avidity has been shown to be essential in several virus systems for the protective effect of neutralizing antibodies, it should be clarified whether high avidity of IgG directed towards RBD indicates protective immunity. If this is the case, monitoring of avidity should be part of the optimization of vaccination programs.

Avidity is defined as the binding strength of immunoglobulin G (IgG) toward its target epitope. Avidity is directly related to affinity, as both processes are determined by the best fit of IgG to epitopes. We confirm and extend data on incomplete avidity maturation of IgG toward severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) nucleoprotein (NP), spike protein‐1 (S1), and its receptor‐binding domain (RBD) in coronavirus disease 2019 (COVID‐19) patients. In SARS‐CoV‐2‐infected individuals, an initial rise in avidity maturation was ending abruptly, leading to IgG of persistently low or intermediate avidity. Incomplete avidity maturation might facilitate secondary SARS‐CoV‐2 infections and thus prevent the establishment of herd immunity. Incomplete avidity maturation after infection with SARS‐CoV‐2 (with only 11.8% of cases showing finally IgG of high avidity, that is, an avidity index > 0.6) was contrasted by regular and rapid establishment of high avidity in SARS‐CoV‐2 naïve individuals after two vaccination steps with the BioNTech messenger RNA (mRNA) Vaccine (78% of cases with high avidity). One vaccination step was not sufficient for induction of complete avidity maturation in vaccinated SARS‐CoV‐2 naïve individuals, as it induced high avidity only in 2.9% of cases within 3 weeks. However, one vaccination step was sufficient to induce high avidity in individuals with previous SARS‐CoV‐2 infection.

The mitochondrial Rieske iron-sulfur protein is an obligatory component of the respiratory electron transport chain that is encoded by a single-copy gene in mammals and fungi. In contrast, this protein is encoded by a small gene family in dicotyledonous tobacco and monocotyledonous maize. We cloned four cDNAs from tobacco that encode the mitochondrial Rieske iron-sulfur protein. These clones, along with a previously isolated cDNA, represent five independent members of the gene family that can be divided into three subfamilies. All of these genes were derived from the two progenitor species and were expressed in amphidiploid tobacco. The proteins encoded by these five genes are probably functional because they all contain the universally conserved hexyl peptides necessary for the 2Fe-2S cluster formation. The expression of the Rieske protein gene family is differentially regulated; a 6- to 11-fold higher level of steady state transcripts was found in flowers than in leaves, stems, and roots. Members of at least two subfamilies were preferentially expressed in flowers, indicating that they share a common cis-regulatory element(s), which can respond to a flower-specific signal(s). Although approximately 10 times more transcripts occurred in flowers than in leaves, flower and leaf mitochondria contained a similar amount of the Rieske protein. Flowers, however, contained seven times more Rieske proteins than leaves. These results indicated an increase in mitochondrion number in flowers. High-energy demands during anther development might bring about an increase in mitochondrion numbers in flowers and the flower-enhanced expression of the Rieske protein gene family. Our results suggested that nuclear genes encoding mitochondrial respiratory proteins could sense and respond to changes in energy metabolism and/or changes in mitochondrion numbers.

The mitochondrial Rieske iron-sulfur protein is an obligatory component of the respiratory electron transport chain that is encoded by a single-copy gene in mammals and fungi. In contrast, this protein is encoded by a small gene family in dicotyledonous tobacco and monocotyledonous maize. We cloned four cDNAs from tobacco that encode the mitochondrial Rieske iron-sulfur protein. These clones, along with a previously isolated cDNA, represent five independent members of the gene family that can be divided into three subfamilies. All of these genes were derived from the two progenitor species and were expressed in amphidiploid tobacco. The proteins encoded by these five genes are probably functional because they all contain the universally conserved hexyl peptides necessary for the 2Fe-2s cluster formation. The expression of the Rieske protein gene family is differentially regulated; a 6-to 11-fold higher leve1 of steady state transcripts was found in flowers than in leaves, stems, and roots. Members of at least two subfamilies were preferentially expressed in flowers, indicating that they share a common cis-regulatory element(s), which can respond to a flowerspecific signal(s). Although -10 times more transcripts occurred in flowers than in leaves, flower and leaf mitochondria contained a similar amount of the Rieske protein. Flowers, however, contained seven times more Rieske proteins than leaves. These results indicated an increase in mitochondrion number in flowers. High-energy demands during anther development might bring about an increase in mitochondrion numbers in flowers and the flower-enhanced expression of the Rieske protein gene family. Our results suggested that nuclear genes encoding mitochondrial respiratory proteins could sense and respond to changes in energy metabolism andlor changes in mitochondrion numbers. INTRODUCTIONThe mitochondrial electron transport chain of eukaryotes consists of four major multimeric enzyme complexes, one of which is the ubiquino1:cytochrome c oxidoreductase, commonly referred to as the cytochrome bcl complex or complex III. Electron flow through the cytochrome bcl complex is coupled with a vectorial transmembrane proton translocation, which generates an electrochemical gradient that is subsequently used for the synthesis of ATP by the Fo/Fl ATPase located in the mitochondrial inner membrane (for review, see Trumpower, 1981). The enzyme complex has been purified from bacteria (Yang and Trumpower, 1986), fungi (Siedow et al., 1978;Weiss and Kolb, 1979), plants (Nakajimaet al., 1984;Berry et al., 1991;Braun and Schmitz, 1992), and mammals (Rieske et al., 1964). Although the number of subunits in the complex varies from as few as three in some bacteria to as many as 11 in some higher eukaryotes, all bcl complexes contain a core of three catalytic subunits, including cytochrome b, which has two heme groups, cytochrome cl, and the Rieske iron-sulfur protein (RISP) that contains a nonheme 2Fe-2s cluster.To whom correspondence should be addressed.The RlSP was first observed in ...

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