The McdAB system positions α‐carboxysomes in proteobacteria

Abstract

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Positioning the Model Bacterial Organelle, the Carboxysome

“…ParB proteins bind specifically to DNA-binding sites on a chromosome or plasmid, thus demarcating the genetic element as "cargo" for positioning by the cognate ParA. Consistently, a small partner protein expressed downstream of the mcdA gene, and in the same operon, was recently discovered called McdB (40,41). McdB proteins strongly colocalize with b-carboxysomes in S. elongatus (Fig.…”

“…In general, H. neapolitanus a-carboxysomes are greater in number (4 to 18) and smaller (40-to 200-nm diameter) compared to the fewer (3 to 5) and larger (90 to 600 nm) b-carboxysomes of S. elongatus (40,54,76,78,84,86). Despite these differences, H. neapolitanus a-carboxysomes are also distributed down the cell length (14,41,87).…”

“…In the absence of either McdA or McdB, aand b-carboxysomes still self-assemble but form aggregates that largely mislocalize toward polar regions of the cell (40,41). Interestingly, the degradation of inactive carboxysomes was recently found to also occur near polar regions of a cyanobacterial cell (109).…”

“…Second, we introduce the twocomponent McdAB system and summarize its proposed diffusion-ratchet mechanism of carboxysome positioning (40). We then highlight recent work showing that McdAB systems are widespread among carboxysome-containing bacteria (41,44). We also discuss recent findings that suggest how LLPS may play key roles in carboxysome homeostasis (12,(43)(44)(45)(46)(47).…”

“…Despite their importance, little is known about the mechanisms used by bacteria to regulate BMC "homeostasis," a term we use here to encompass the dynamic equilibrium among the interrelated aspects of BMC assembly, composition, size, copy number, maintenance, turnover, positioning, and ultimately, function in the cell. In this minireview, we focus on the only known BMC positioning system to date-the maintenance of carboxysome distribution (Mcd) system, which spatially organizes carboxysomes (40,41). We start with a general overview of carboxysome biology, as this is the focus of a number of excellent recent reviews (42,43).…”