Article

R UBISCO : Structure, Regulatory Interactions, and Possibilities for a Better Enzyme

Department of Biochemistry, Institute of Agriculture and Natural Resources, University of Nebraska, Lincoln, Nebraska 68588-0664, USA.
Annual review of plant biology (Impact Factor: 23.3). 02/2002; 53(1):449-75. DOI: 10.1146/annurev.arplant.53.100301.135233
Source: PubMed

ABSTRACT

Ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (Rubisco) catalyzes the first step in net photosynthetic CO2 assimilation and photorespiratory carbon oxidation. The enzyme is notoriously inefficient as a catalyst for the carboxylation of RuBP and is subject to competitive inhibition by O2, inactivation by loss of carbamylation, and dead-end inhibition by RuBP. These inadequacies make Rubisco rate limiting for photosynthesis and an obvious target for increasing agricultural productivity. Resolution of X-ray crystal structures and detailed analysis of divergent, mutant, and hybrid enzymes have increased our insight into the structure/function relationships of Rubisco. The interactions and associations relatively far from the Rubisco active site, including regulatory interactions with Rubisco activase, may present new approaches and strategies for understanding and ultimately improving this complex enzyme.

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Available from: Michael E Salvucci
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    • "In wheat, variation in V c has been observed across different genotypes and it has been suggested that many of the catalytic properties of Rubisco are determined by the large subunit (Evans and Austin, 1986;Terachi et al., 1987;Kasai et al., 1997), which contains the catalytic sites. The rbcL gene is chloroplast encoded (Spreitzer and Salvucci, 2002) and the chloroplast genome tends to be evolutionarily highly conserved . However, within the Poaceae, rbcL has evolved at a relatively rapid rate compared with other families of flowering plants (Bousquet et al., 1992;Gaut et al., 1992). "
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    ABSTRACT: Rubisco is a major target for improving crop photosynthesis and yield, yet natural diversity in catalytic properties of this enzyme is poorly understood. Rubisco from 25 genotypes of the Triticeae tribe, including wild relatives of bread wheat (Triticum aestivum), were surveyed to identify superior enzymes for improving photosynthesis in this crop. In vitro Rubisco carboxylation velocity (V c), Michaelis–Menten constants for CO2 (K c) and O2 (K o) and specificity factor (S c/o) were measured at 25 and 35 °C. V c and K c correlated positively, while V c and S c/o were inversely related. Rubisco large subunit genes (rbcL) were sequenced, and predicted corresponding amino acid differences analysed in relation to the corresponding catalytic properties. The effect of replacing native wheat Rubisco with counterparts from closely related species was analysed by modelling the response of photosynthesis to varying CO2 concentrations. The model predicted that two Rubisco enzymes would increase photosynthetic performance at 25 °C while only one of these also increased photosynthesis at 35 °C. Thus, under otherwise identical conditions, catalytic variation in the Rubiscos analysed is predicted to improve photosynthetic rates at physiological CO2 concentrations. Naturally occurring Rubiscos with superior properties amongst the Triticeae tribe can be exploited to improve wheat photosynthesis and crop productivity.
    Full-text · Article · Jan 2016 · Journal of Experimental Botany
    • "Feng et al. ( 2007 ) have shown that the overexpression of SBPase in rice plants increased CO 2 assimilation and enhanced tolerance to high temperatures in young seedlings by maintaining the activity of Rubisco. The thermal inactivation of Rubisco is primarily attributed to the temperature-dependent inactivation of Rubisco activase (Portis 2003 ; Spreitzer and Salvucci 2002 ). Therefore, the activation state of the Rubisco and the CO 2 assimilation rate decrease in concert, once the leaf temperature exceeds the optimum for photosynthesis. "
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    ABSTRACT: Climate change and global warming are considered to be major threats for agricultural production and food safety. Decreased yield of several important crops has already been related to frequently occurring extreme environmental conditions such as heat waves. Since most of the economically and dietary important crops are sensitive to high temperatures, the development of cultivars that can withstand adverse temperatures is a prerequisite for meeting the demands for increased food production. The processes of sensing and responding to heat are complex phenomena in plants which comprise the activation of numerous regulatory and signaling pathways that eventually lead to a fine metabolic adjustment to ensure cell survival. Currently, our knowledge of heat stress response is greatly advanced by the massive production of datasets derived from -omics studies which supplement the current models with new genes, proteins, and metabolites or even introduce whole new pathways. This information is essential for the improvement of plant thermotolerance either through breeding programs or approaches using genetic engineering. This chapter contains an assembly of several aspects regarding heat stress response and thermotolerance. The effects of high temperatures on major aspects of plant growth and development are described, and different methods for thermotolerance screening are presented. In addition, putative heat sensing mechanisms are discussed and the most important metabolic changes are elaborated. Last, a summary of efforts and strategies to improve thermotolerance by breeding or genetic engineering is given.
    No preview · Chapter · Jan 2016
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    • "However, RubisCO is a sluggish catalyst and its efficiency is further limited by its poor ability to discriminate between the gaseous substrates CO2 and O2 (Spreitzer and Salvucci, 2002;Andersson, 2008), with the oxygen fixation reaction leading to energetically wasteful metabolism. Because of RubisCO's importance in CO2 bioconversions, a number of studies have endeavoured to increase carbon capture through various artificial evolution and bioengineering methods to produce RubisCO enzymes with increased activity or higher CO2 specificity (Spreitzer and Salvucci, 2002;Smith and Tabita, 2003;Parikh et al., 2006;Yoshida et al., 2007;Mueller-Cajar and Whitney, 2008;Satagopan et al., 2009;2014;Cai et al., 2014;Lin et al., 2014). While these and recent studies to manipulate the properties of RubisCO are especially promising (Lin et al., 2014;Hauser et al., 2015), it is clear that sequence or structural analyses alone are not accurate predictors of enzyme function. "
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    ABSTRACT: Ribulose 1, 5-bisphosphate carboxylase/oxygenase (RubisCO) is a critical yet severely inefficient enzyme that catalyzes the fixation of virtually all of the carbon found on Earth. Here, we report a functional metagenomic selection that recovers physiologically-active RubisCO molecules directly from uncultivated and largely unknown members of natural microbial communities. Selection is based on CO2 -dependent growth in a host strain capable of expressing environmental DNA, precluding the need for pure cultures or screening of recombinant clones for enzymatic activity. Seventeen functional RubisCO-encoded sequences were selected using DNA extracted from soil and river autotrophic enrichments, a photosynthetic biofilm, and a subsurface groundwater aquifer. Notably, three related form II RubisCOs were recovered which share high sequence similarity with metagenomic scaffolds from uncultivated members of the Gallionellaceae family. One of the Gallionellaceae RubisCOs was purified and shown to possess CO2 /O2 specificity typical of form II enzymes. X-ray crystallography determined that this enzyme is a hexamer, only the second form II multimer ever solved and the first RubisCO structure obtained from an uncultivated bacterium. Functional metagenomic selection leverages natural biological diversity and billions of years of evolution inherent in environmental communities, providing a new window into the discovery of CO2 -fixing enzymes not previously characterized.
    Full-text · Article · Nov 2015 · Environmental Microbiology
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