Structure and identification of a pterin dehydratase-like protein as a ribulose-bisphosphate carboxylase/oxygenase (RuBisCO) assembly factor in the α-carboxysome.
Carboxysomes are proteinaceous bacterial microcompartments that increase the efficiency of the rate-limiting step in carbon fixation by sequestering reaction substrates. Typically, α-carboxysomes are genetically encoded as a single operon expressing the structural proteins and the encapsulated enzymes of the microcompartment. In addition, depending on phylogeny, as many as 13 other genes are found to co-occur near or within α-carboxysome operons. One of these genes codes for a protein with distant homology to pterin-4α-carbinolamine dehydratase (PCD) enzymes. It is present in all α-carboxysome containing bacteria and has homologs in algae and higher plants. Canonical PCDs play an important role in amino acid hydroxylation, a reaction not associated with carbon fixation. We determined the crystal structure of an α-carboxysome PCD-like protein from the chemoautotrophic bacterium Thiomonas intermedia K12, at 1.3-Å resolution. The protein retains a three-dimensional fold similar to canonical PCDs, although the prominent active site cleft present in PCD enzymes is disrupted in the α-carboxysome PCD-like protein. Using a cell-based complementation assay, we tested the PCD-like proteins from T. intermedia and two additional bacteria, and found no evidence for PCD enzymatic activity. However, we discovered that heterologous co-expression of the PCD-like protein from Halothiobacillus neapolitanus with RuBisCO and GroELS in Escherichia coli increased the amount of soluble, assembled RuBisCO recovered from cell lysates compared with co-expression of RuBisCO with GroELS alone. We conclude that this conserved PCD-like protein, renamed here α-carboxysome RuBisCO assembly factor (or acRAF), is a novel RuBisCO chaperone integral to α-carboxysome function.
From the Molecular Biology Interdepartmental Ph.D. Program and.
Nicole M
NM
Wheatley
Christopher D
CD
Sundberg
Soheil D
SD
Gidaniyan
Duilio
D
Cascio
Todd O
TO
Yeates
D042521:Burkholderiaceae / Q000201:enzymology / Q000235:genetics; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D005816:Genetic Complementation Test; D006836:Hydro-Lyases / Q000737:chemistry*; D008958:Models, Molecular; D018832:Molecular Chaperones / Q000737:chemistry; D009876:Operon; D011485:Protein Binding; D017433:Protein Structure, Secondary; D011622:Pterins / Q000737:chemistry; D012273:Ribulose-Bisphosphate Carboxylase / Q000737:chemistry*
D018832:Molecular Chaperones; D011622:Pterins; D012273:Ribulose-Bisphosphate Carboxylase; D006836:Hydro-Lyases; C076392:pterin-4a-carbinolamine dehydratase
Carbon Dioxide; Carbon Fixation; Carboxysome; Molecular Chaperone; Protein Assembly; Protein Evolution; Protein Folding; Pseudo-enzyme; Pterin Dehydratase; RuBisCO