Crystal structure of P. falciparum Cpn60 bound to ATP reveals an open dynamic conformation before substrate binding

Plasmodium falciparum harbors group 1 and group 2 chaperonin systems to mediate the folding of cellular proteins in different cellular locations. Two distinct group 1 chaperonins operate in the organelles of mitochondria and apicoplasts, while group 2 chaperonins function in the cytosol. No structural information has been reported for any chaperonin from plasmodium. In this study, we describe the crystal structure of a double heptameric ring Plasmodium falciparum mitochondrial chaperonin 60 (Cpn60) bound with ATP, which differs significantly from any known crystal structure of chaperonin 60. The structure likely represents a unique intermediate state during conformational conversion from the closed state to the opened state. Three of the seven apical domains are highly dynamic while the equatorial domains form a stable ring. The structure implies large movements of the apical domain in the solution play a role in nucleotide-dependent regulation of substrate binding and folding. A unique 26–27 residue insertion in the equatorial domain of Plasmodium falciparum mitochondrial chaperonin greatly increases both inter-ring and intra-ring subunit–subunit interactions. The present structure provides new insights into the mechanism of Cpn60 in chaperonin assembly and function.

Brief report: Expression of TNF-α in chronic periapical lesions correlates with expression of bacterial chaperonin-60

Background/Aim: The aim of this study is to determine the quantitative expression of the bacterial heat shock protein, Chaperonin-60 (Cpn60) and pro-inflammatory and anti-inflammatory cytokine in periapical tissue, obtained from individuals with chronic periapical lesions and to determine the correlation between the expression of the bacterial heat shock protein and the expression of these cytokines. Methods. The study was performed on 18 periapical lesions and 6 control samples of healthy periapical tissue, taken at the Clinic of Dental Medicine, Faculty of Medical 4 Sciences University of Pristina, Kosovska Mitrovica. The levels of mRNA expression of pro- and anti- inflammatory cytokines and bacterial heat shock protein were determined by real time quantitative RT-PCR. Results. Analysis revealed significantly higher mRNA levels of TNF-? and Cpn60 in the tissue of periapical lesions compared with normal periapical tissue (P <0.05). Contrary to these results, the mRNA expression of anti-inflammatory IL-10 was significantly higher in the samples of normal periapical tissue compared with the mRNA levels of this cytokine in the tissue of periapical lesions (P <0.001). Expression of Cpn60 is in strong correlation with TNF-? expression in periapical lesions. Conclusion. Cpn60 released from bacteria in periapical tissue could be a strong stimulator of inflammatory response and one of the important players in the pathogenesis of periapical lesions.

OsCpn60β1 is Essential for Chloroplast Development in Rice (Oryza sativa L.)

The chaperonin 60 (Cpn60) protein is of great importance to plants due to its involvement in modulating the folding of numerous chloroplast protein polypeptides. In chloroplasts, Cpn60 is differentiated into two subunit types—Cpn60α and Cpn60β and the rice genome encodes three α and three β plastid chaperonin subunits. However, the functions of Cpn60 family members in rice were poorly understood. In order to investigate the molecular mechanism of OsCpn60β1, we attempted to disrupt the OsCpn60β1 gene by CRISPR/Cas9-mediated targeted mutagenesis in this study. We succeeded in the production of homozygous OsCpn60β1 knockout rice plants. The OsCpn60β1 mutant displayed a striking albino leaf phenotype and was seedling lethal. Electron microscopy observation demonstrated that chloroplasts were severely disrupted in the OsCpn60β1 mutant. In addition, OsCpn60β1 was located in the chloroplast and OsCpn60β1 is constitutively expressed in various tissues particularly in the green tissues. The label-free qualitative proteomics showed that photosynthesis-related pathways and ribosomal pathways were significantly inhibited in OsCpn60β1 mutants. These results indicate that OsCpn60β1 is essential for chloroplast development in rice.

Correction: Chaperonin 60 sustains osteoblast autophagy and counteracts glucocorticoid aggravation of osteoporosis by chaperoning RPTOR

Following publication of this article, the authors realized that there were 1) errors made in the author affiliations and that 2) a typo in a grant number needed to be corrected. The corrected author affiliations and grant numbers are listed below. We apologize for the inconvenience.

PAB is an assembly chaperone that functions downstream of chaperonin 60 in the assembly of chloroplast ATP synthase coupling factor 1

The chloroplast ATP synthase, a multisubunit complex in the thylakoid membrane, catalyzes the light-driven synthesis of ATP, thereby supplying the energy for carbon fixation during photosynthesis. The chloroplast ATP synthase is composed of both nucleus- and chloroplast-encoded proteins that have required the evolution of novel mechanisms to coordinate the biosynthesis and assembly of chloroplast ATP synthase subunits temporally and spatially. Here we have elucidated the assembly mechanism of the α3β3γ core complex of the chloroplast ATP synthase by identification and functional characterization of a key assembly factor, PAB (PROTEIN IN CHLOROPLAST ATPASE BIOGENESIS). PAB directly interacts with the nucleus-encoded γ subunit and functions downstream of chaperonin 60 (Cpn60)-mediated CF1γ subunit folding to promote its assembly into the catalytic core. PAB does not have any recognizable motifs or domains but is conserved in photosynthetic eukaryotes. It is likely that PAB evolved together with the transfer of chloroplast genes into the nucleus to assist nucleus-encoded CF1γ assembly into the CF1 core. Such coordination might represent an evolutionarily conserved mechanism for folding and assembly of nucleus-encoded proteins to ensure proper assembly of multiprotein photosynthetic complexes.