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A synthetic biology window into hornwort Rubisco assembly and its kinetics

ABSTRACT: Heterologous expression of hornwort Rubisco from Anthoceros agrestis in Escherichia coliwith expression of Rubisco large and small subunits, chaperonins 60alpha/beta and chaperonin 20 as well as a suite of assembly factors, Raf1/Raf2/RbcX2/BSD2/RbcX1. Rubisco kinetics show differences in Rubisco assembled with and without RbcX1/2.

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ORGANISM(S): Anthoceros Agrestis

SUBMITTER: Zhen Guo Oh

LAB HEAD: Laura Gunn

PROVIDER: PXD052489 | Pride | 2024-11-04

REPOSITORIES: Pride

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Project description:The slow kinetics and poor substrate specificity of the key photosynthetic CO2-fixing enzyme Rubisco have prompted the repeated evolution of Rubisco containing compartments known as pyrenoids in diverse algal lineages and carboxysomes in prokaryotes. Inside these compartments actively transported bicarbonate is converted into CO2 gas, which saturates the carboxylase with its substrate. Using co-immunoprecipitation experiments in Phaeodactylum tricornutum we have identified the Rubisco linker protein PYCO1. Similar to the green algal Rubisco linker protein EPYC1, PYCO1 is intrinsically disordered, possesses repeats and is positively charged at physiological pH. However, it possesses no sequence similarity to EPYC1, as expected for convergent evolution of a red Rubisco containing pyrenoid. Fluorescent PYCO1 fusion proteins localize as a rod shaped structure in the diatom chloroplast, consistent with the shape of the pyrenoid defined by transmission electron microscopy. To test the hypothesis that PYCO1 is the diatom pyrenoid scaffold we produced pure protein in Escherichia coli. Recombinant PYCO1 protein undergoes homotypic liquid liquid phase separation in a salt dependent manner. Diatom Rubisco specifically partitions into PYCO1 condensates. Heterotypic PYCO1-Rubisco condensates can bind up to three Rubisco hexadecamers per PYCO1 protein. Rubisco carboxylase function is unaffected in the condensates. PYCO1 is highly mobile in homotypic condensates. In contrast PYCO1 condensates saturated with diatom Rubisco have greatly reduced dynamics, with both PYCO1 and Rubisco becoming immobile. Consistently, FRAP experiments indicate that PYCO1 is not mobile in vivo. A combination of Cryo-electron microscopy and site-directed mutagenesis data show that the KWSP motif found in PYCO1 repeats binds to small subunits at the entrance of the Rubisco hexadecamer’s solvent channel. Analysis of mutant PYCO1 proteins show that both the “KWSP” tryptophan and another repeating tyrosine are essential for homotypic phase separation. We speculate that the unusual material properties of the PYCO1-Rubisco condensate are necessary to support the unusual non-spherical shape of the Phaeodactylum pyrenoid. Careful characterization of multiple diverse Rubisco condensates will strengthen translational approaches aiming to introduce pyrenoids and other metabolic condensates into new host organisms.

			Action	DRS
	AaRbc.raw	Raw
	AaRbcwandwoRbcx.msf	Msf
	AaRbcwithoutRbcX.raw	Raw
	BL21DE3proteome.fasta	Fasta
	MSgel.PNG	Other

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A synthetic biology window into hornwort Rubisco assembly and its kinetics

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