scholarly journals The McdAB system positions α-carboxysomes in proteobacteria

2020 ◽  
Author(s):  
Joshua S. MacCready ◽  
Lisa Tran ◽  
Joseph L. Basalla ◽  
Pusparanee Hakim ◽  
Anthony G. Vecchiarelli
Keyword(s):  
Carbon Fixation ◽  
Synechococcus Elongatus ◽  
Bacterial Protein ◽  
Metabolic Processes ◽  
Two Component System ◽  
Component System ◽  
Two Component ◽  
Pcc 7942

SummaryCarboxysomes are protein-based organelles essential for carbon fixation in cyanobacteria and proteobacteria. Previously, we showed that the cyanobacterial nucleoid is utilized as a surface for the equidistant-spacing of β-carboxysomes across cell lengths by a two-component system (McdAB) in the model cyanobacterium Synechococcus elongatus PCC 7942. More recently, we found that McdAB systems are widespread among β-cyanobacteria, which possess β-carboxysomes, but are absent in α-cyanobacteria, which possess structurally distinct α-carboxysomes. Since cyanobacterial α-carboxysomes are thought to have arisen in proteobacteria and were subsequently horizontally transferred into cyanobacteria, this raised the question whether α-carboxysome containing proteobacteria possess a McdAB system for positioning α-carboxysomes. Here, using the model chemoautotrophic proteobacterium H. neapolitanus, we show that a McdAB system distinct from that of β-cyanobacteria operates to position α-carboxysomes across cell lengths. We further show that this system is widespread among α-carboxysome containing proteobacteria and that cyanobacteria likely inherited an α-carboxysome operon from a proteobacterium lacking the mcdAB locus. These results demonstrate that McdAB is a cross-phylum two-component system necessary for positioning α- and β-carboxysomes. The findings have further implications for understanding the positioning of other bacterial protein-based organelles involved in diverse metabolic processes.

scholarly journals Dissection of the ATPase active site of McdA reveals the sequential steps essential for carboxysome distribution

2021 ◽  
pp. mbc.E21-03-0151
Author(s):  
Pusparanee Hakim ◽  
Y Hoang ◽  
Anthony G. Vecchiarelli
Keyword(s):  
Active Site ◽  
Carbon Fixation ◽  
Binding Region ◽  
Two Component System ◽  
Component System ◽  
Ratchet Mechanism ◽  
Bacterial Microcompartment ◽  
Two Component ◽  
Bacterial Nucleoid

Carboxysomes, the most prevalent and well-studied anabolic bacterial microcompartment, play a central role in efficient carbon fixation by cyanobacteria and proteobacteria. In previous studies, we identified the two-component system called McdAB that spatially distributes carboxysomes across the bacterial nucleoid. McdA, a ParA-like ATPase, forms a dynamic oscillating gradient on the nucleoid in response to carboxysome-localized McdB. As McdB stimulates McdA ATPase activity, McdA is removed from the nucleoid in the vicinity of carboxysomes, propelling these proteinaceous cargos toward regions of highest McdA concentration via a Brownian-ratchet mechanism. How the ATPase cycle of McdA governs its in vivo dynamics and carboxysome positioning remains unresolved. Here, by strategically introducing amino acid substitutions in the ATP-binding region of McdA, we sequentially trap McdA at specific steps in its ATP cycle. We map out critical events in the ATPase cycle of McdA that allows the protein to bind ATP, dimerize, change its conformation into a DNA-binding state, interact with McdB-bound carboxysomes, hydrolyze ATP and release from the nucleoid. We also find that McdA is a member of a previously unstudied subset of ParA family ATPases, harboring unique interactions with ATP and the nucleoid for trafficking their cognate intracellular cargos. [Media: see text] [Media: see text] [Media: see text]

scholarly journals Dissection of the ATPase active site of McdA reveals the sequential steps essential for carboxysome distribution

2021 ◽  
Author(s):  
Pusparanee Hakim ◽  
Anthony G. Vecchiarelli
Keyword(s):  
Active Site ◽  
Carbon Fixation ◽  
Binding Region ◽  
Two Component System ◽  
Component System ◽  
Ratchet Mechanism ◽  
Bacterial Microcompartment ◽  
Two Component ◽  
Bacterial Nucleoid

ABSTRACTCarboxysomes, the most prevalent and well-studied anabolic bacterial microcompartment, play a central role in efficient carbon fixation by cyanobacteria and proteobacteria. In previous studies, we identified the two-component system called McdAB that spatially distributes carboxysomes across the bacterial nucleoid. McdA, a ParA-like ATPase, forms a dynamic oscillating gradient on the nucleoid in response to carboxysome-localized McdB. As McdB stimulates McdA ATPase activity, McdA is removed from the nucleoid in the vicinity of carboxysomes, propelling these proteinaceous cargos toward regions of highest McdA concentration via a Brownian-ratchet mechanism. However, how the ATPase cycle of McdA governs its in vivo dynamics and carboxysome positioning remains unresolved. Here, by strategically introducing amino acid substitutions in the ATP-binding region of McdA, we sequentially trap McdA at specific steps in its ATP cycle. We map out critical events in the ATPase cycle of McdA that allows the protein to bind ATP, dimerize, change its conformation into a DNA-binding state, interact with McdB-bound carboxysomes, hydrolyze ATP and release from the nucleoid. We also find that McdA is a member of a previously unstudied subset of ParA family ATPases, harboring unique interactions with ATP and the nucleoid for trafficking their cognate intracellular cargos.

scholarly journals Iron oxidation is regulated by the two-component system, RegSR, and plays a role in photolithoheterotrophic growth in Rhodopseudomonas palustris

2021 ◽  
Author(s):  
Nicholas W Haas ◽  
Abhiney Jain ◽  
Zachary Hying ◽  
Sabrina J Arif ◽  
Jeffrey A Gralnick ◽  
...  
Keyword(s):  
Carbon Fixation ◽  
Rhodopseudomonas Palustris ◽  
Iron Oxidation ◽  
Anaerobic Respiration ◽  
Carbon Substrate ◽  
Two Component System ◽  
Component System ◽  
Two Component ◽  
Oxidized Carbon

Purple nonsulfur bacteria (PNSB) are metabolically versatile organisms generate energy through both aerobic and anaerobic respiration as well as anoxygenic photosynthesis. In many PNSB, the redox-sensing, two-component system RegBA is a global regulator of energy generating and consuming pathways, such as photosynthesis, carbon fixation, and nitrogen fixation, when cells are shifted from an aerobic to an anaerobic environment. However, in the PNSB Rhodopseudomonas palustris, the role of the RegBA homolog, RegSR, was unclear since global regulation of these same pathways involves the oxygen-sensing signal transduction system, FixJL-K, in R. palustris. Using RNA-seq analysis, we found that RegSR plays a role in regulating the operon pioABC, which encodes genes required for Fe(II) oxidation. We found that transcript levels of pioABC under photoheterotrophic conditions was dependent on the oxidation state of the carbon substrate and whether the cells were fixing nitrogen. We also found that R. palustris can carry out photolithoheterotrophic growth using Fe(II) oxidation when grown with the oxidized carbon substrate, malate, requiring regSR and pioABC. We present a model in which RegSR regulates pioABC in response to a cellular redox signal, allowing R. palustris to use Fe(II) oxidation to access more electrons when there is an increased cellular demand for reducing equivalents.

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