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Publication Abstract from PubMed

Hornworts are the only land plants that employ a pyrenoid to optimize Rubisco's CO(2) fixation. Yet, hornwort Rubisco remains poorly characterized. Here we assemble the hornwort Anthoceros agrestis Rubisco (AaRubisco) using the Arabidopsis thaliana SynBio expression system and observed the formation of stalled intermediates, prompting us to develop a new SynBio system with A. agrestis cognate chaperones. We successfully assembled AaRubisco and Rubisco from three other hornwort species. Unlike A. thaliana Rubisco, AaRubisco assembly is not dependent on RbcX or Raf2. Kinetic characterization reveals that hornwort Rubiscos exhibit a range of catalytic rates (3-10 s(-1)), but with similar affinity ( approximately 30 muM) and specificity ( approximately 70) for CO(2). In other words, hornwort Rubiscos do not comply with the long held canonical catalytic trade-off observed in other land plants, providing experimental support that Rubisco kinetics may be phylogenetically constrained. Unexpectedly, we observed a 50% increase in AaRubisco catalytic rates when RbcX was removed from our SynBio system, without any reduction in specificity. Structural biology, biochemistry and proteomic analysis suggest that subtle differences in Rubisco large subunit interactions, when RbcX is absent during biogenesis, increases the accessibility of active sites and catalytic turnover rate. This study uncovered a previously unknown Rubisco kinetic parameter space and provides a SynBio chassis to expand the survey of other Rubisco kinetics. Our discovery could thus reshape the approaches for engineering Rubisco with superior kinetics.

Unique biogenesis and kinetics of hornwort Rubiscos revealed by synthetic biology systems.,Oh ZG, Robison TA, Loh DH, Leong Ang WS, Ng J, Li FW, Gunn LH Mol Plant. 2024 Nov 2:S1674-2052(24)00352-6. doi: 10.1016/j.molp.2024.10.013. PMID:39491367^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.