A Chaperonin Subunit with Unique Structures Is Essential for Folding of a Specific Substrate

Type I chaperonins are large, double-ring complexes present in bacteria (GroEL), mitochondria (Hsp60), and chloroplasts (Cpn60), which are involved in mediating the folding of newly synthesized, translocated, or stress-denatured proteins. In Escherichia coli, GroEL comprises 14 identical subunits and has been exquisitely optimized to fold its broad range of substrates. However, multiple Cpn60 subunits with different expression profiles have evolved in chloroplasts. Here, we show that, in Arabidopsis thaliana, the minor subunit Cpn60β4 forms a heterooligomeric Cpn60 complex with Cpn60α1 and Cpn60β1–β3 and is specifically required for the folding of NdhH, a subunit of the chloroplast NADH dehydrogenase-like complex (NDH). Other Cpn60β subunits cannot complement the function of Cpn60β4. Furthermore, the unique C-terminus of Cpn60β4 is required for the full activity of the unique Cpn60 complex containing Cpn60β4 for folding of NdhH. Our findings suggest that this unusual kind of subunit enables the Cpn60 complex to assist the folding of some particular substrates, whereas other dominant Cpn60 subunits maintain a housekeeping chaperonin function by facilitating the folding of other obligate substrates

Chlorophyll Fluorescence Measurements in Arabidopsis Plants Using a Pulse-amplitude-modulated (PAM) Fluorometer

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Ribosome rescue activity of an Arabidopsis thaliana ArfB homolog

A homolog of the bacterial ribosome rescue factor ArfB was identified in Arabidopsis thaliana. The factor, named AtArfB for Arabidopsis thaliana ArfB, showed ribosome rescue activity in both in vivo and in vitro assays based on the bacterial translation system. As has been shown for ArfB, the ribosome rescue activity of AtArfB was dependent on the GGQ motif, the crucial motif for the function of class I release factors and ArfB. The C-terminal region of AtArfB was also important for its function. The N-terminal region of AtArfB, which is absent in bacterial ArfB, functioned as a transit peptide for chloroplast targeting in tobacco cells. These results strongly suggest that AtArfB is a ribosome rescue factor that functions in chloroplasts

Japan\u27s Lagging Gender Equality

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Maximizing the Potential of Scientists in Japan: promoting equal participation for women scientists through leadership development

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Hydroponic Culture of ‘Micro-Tom’ Tomato

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