Excess Copper-Induced Alterations of Protein Profiles and Related Physiological Parameters in Citrus Leaves

This present study examined excess copper (Cu) effects on seedling growth, leaf Cu concentration, gas exchange, and protein profiles identified by a two-dimensional electrophoresis (2-DE) based mass spectrometry (MS) approach after Citrus sinensis and Citrus grandis seedlings were treated for six months with 0.5 (control), 200, 300, or 400 μM CuCl2. Forty-one and 37 differentially abundant protein (DAP) spots were identified in Cu-treated C. grandis and C. sinensis leaves, respectively, including some novel DAPs that were not reported in leaves and/or roots. Most of these DAPs were identified only in C. grandis or C. sinensis leaves. More DAPs increased in abundances than DAPs decreased in abundances were observed in Cu-treated C. grandis leaves, but the opposite was true in Cu-treated C. sinensis leaves. Over 50% of DAPs were associated with photosynthesis, carbohydrate, and energy metabolism. Cu-toxicity-induced reduction in leaf CO2 assimilation might be caused by decreased abundances of proteins related to photosynthetic electron transport chain (PETC) and CO2 assimilation. Cu-effects on PETC were more pronounced in C. sinensis leaves than in C. grandis leaves. DAPs related to antioxidation and detoxification, protein folding and assembly (viz., chaperones and folding catalysts), and signal transduction might be involved in Citrus Cu-toxicity and Cu-tolerance.

Assembly pathway of a bacterial complex iron sulfur molybdoenzyme

Protein folding and assembly into macromolecule complexes within the living cell are complex processes requiring intimate coordination. The biogenesis of complex iron sulfur molybdoenzymes (CISM) requires use of a system specific chaperone – a redox enzyme maturation protein (REMP) – to help mediate final folding and assembly. The CISM dimethyl sulfoxide (DMSO) reductase is a bacterial oxidoreductase that utilizes DMSO as a final electron acceptor for anaerobic respiration. The REMP DmsD strongly interacts with DMSO reductase to facilitate folding, cofactor-insertion, subunit assembly and targeting of the multi-subunit enzyme prior to membrane translocation and final assembly and maturation into a bioenergetic catalytic unit. In this article, we discuss the biogenesis of DMSO reductase as an example of the participant network for bacterial CISM maturation pathways.

Chaperone-assisted degradation: multiple paths to destruction

Molecular chaperones are well known as facilitators of protein folding and assembly. However, in recent years multiple chaperone-assisted degradation pathways have also emerged, including CAP (chaperone-assisted proteasomal degradation), CASA (chaperone-assisted selective autophagy), and CMA (chaperone-mediated autophagy). Within these pathways chaperones facilitate the sorting of non-native proteins to the proteasome and the lysosomal compartment for disposal. Impairment of these pathways contributes to the development of cancer, myopathies, and neurodegenerative diseases. Chaperone-assisted degradation thus represents an essential aspect of cellular proteostasis, and its pharmacological modulation holds the promise to ameliorate some of the most devastating diseases of our time. Here, we discuss recent insights into molecular mechanisms underlying chaperone-assisted degradation in mammalian cells and highlight its biomedical relevance.