Research Article

Plant RuBisCo assembly in E. coli with five chloroplast chaperones including BSD2

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Science  08 Dec 2017:
Vol. 358, Issue 6368, pp. 1272-1278
DOI: 10.1126/science.aap9221

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A biotech tour de force

RuBisCo, the key enzyme of photosynthesis, is a complex of eight large and eight small subunits. It mediates the fixation of atmospheric CO2 in the Calvin-Benson-Bassham cycle. In addition to being enzymatically inefficient, RuBisCo has a problem with distinguishing between CO2 and O2. The fixation of O2 results in the energetically wasteful reaction of photorespiration. Thus, there is a strong incentive to improve RuBisCo's catalytic properties by engineering. However, for decades, it has been impossible to express the enzyme from plants in an easily manipulatable bacterial host. Aigner et al. succeeded in functionally expressing plant RuBisCo in Escherichia coli (see the Perspective by Yeates and Wheatley). This should allow for the systematic mutational analysis of RuBisCo and selection of favorable variants for improved crop yields.

Science, this issue p. 1272; see also p. 1253

Abstract

Plant RuBisCo, a complex of eight large and eight small subunits, catalyzes the fixation of CO2 in photosynthesis. The low catalytic efficiency of RuBisCo provides strong motivation to reengineer the enzyme with the goal of increasing crop yields. However, genetic manipulation has been hampered by the failure to express plant RuBisCo in a bacterial host. We achieved the functional expression of Arabidopsis thaliana RuBisCo in Escherichia coli by coexpressing multiple chloroplast chaperones. These include the chaperonins Cpn60/Cpn20, RuBisCo accumulation factors 1 and 2, RbcX, and bundle-sheath defective-2 (BSD2). Our structural and functional analysis revealed the role of BSD2 in stabilizing an end-state assembly intermediate of eight RuBisCo large subunits until the small subunits become available. The ability to produce plant RuBisCo recombinantly will facilitate efforts to improve the enzyme through mutagenesis.

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