PubMed · 1983264
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1990. Molecular chaperones.. https://pubmed.ncbi.nlm.nih.gov/1983264/
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Vitis vinifera L. cv. 'Thompson Seedless' presents a type of stenospermocarpy in grape where fertilization occurs but seeds abort and fail to develop. To unravel the molecular basis for stenospermocarpy in grapes, subtractive hybridization was carried out in order to isolate differentially regulated genes that participate in the seedlessness machinery. Two 'Thompson' lines, a seeded and a seedless, were screened during different flower developmental stages. One of the genes, that was differentially expressed between the seeded and seedless lines, was the chloroplast chaperonin 21 (ch-Cpn21). ch-Cpn21 is a 21-kDa co-chaperonin polypeptide formed by two GroES-like domains fused together in tandem. Silencing of ch-Cpn21 in Nicotiana benthamiana plants resulted in leaf stunting, chlorosis, as well as ovary necrogenesis leading to seed abortion. Moreover, organ-specific silencing of ch-Cpn21 only in Lycopersicum esculentum fruits resulted in the development of seedless tomatoes. These results suggest that ch-Cpn21 may play a role in seed abortion in stenospermocarpic grapes.
Electron capture dissociation (ECD) of proteins in Fourier transform ion cyclotron resonance mass spectrometry usually leads to charge reduction and backbone-bond cleavage, thereby mostly retaining labile, intramolecular noncovalent interactions. In this report, we evaluate ECD of the 84-kDa noncovalent heptameric gp31 complex and compare this with sustained off-resonance irradiation collisionally activated dissociation (SORI-CAD) of the same protein. Unexpectedly, the 21+ charge state of the gp31 oligomer exhibits a main ECD pathway resulting in a hexamer and monomer, disrupting labile, intermolecular noncovalent bonds and leaving the backbone intact. Unexpectedly, the charge separation over the two products is highly proportional to molecular weight. This indicates that a major charge redistribution over the subunits of the complex does not take place during ECD, in contrast to the behavior observed when using SORI-CAD. We speculate that the ejected monomer retains more of its original structure in ECD, when compared to SORI-CAD. ECD of lower charge states of gp31 does not lead to dissociation of noncovalent bonds. We hypothesize that the initial gas-phase structure of the 21+ charge state is significantly different from the lower charge states. These structural differences result in the different reaction pathways when using ECD.
RNA chaperones are nonspecific nucleic acid binding proteins with long disordered regions that help RNA molecules to adopt its functional conformation. Coronavirus nucleoproteins (N) are nonspecific RNA-binding proteins with long disordered regions. Therefore, we investigated whether transmissible gastroenteritis coronavirus (TGEV) N protein was an RNA chaperone. Purified N protein enhanced hammerhead ribozyme self-cleavage and nucleic acids annealing, which are properties that define RNA chaperones. In contrast, another RNA-binding protein, PTB, did not show these activities. N protein chaperone activity was blocked by specific monoclonal antibodies. Therefore, it was concluded that TGEV N protein is an RNA chaperone. In addition, we have shown that purified severe acute respiratory syndrome (SARS)-CoV N protein also has RNA chaperone activity. In silico predictions of disordered domains showed a similar pattern for all coronavirus N proteins evaluated. Altogether, these data led us to suggest that all coronavirus N proteins might be RNA chaperones.