The SpoIIQ landmark protein has different requirements for septal localization and immobilization

Abstract

Summary Bacillus subtilis sporulation depends on the forespore membrane protein SpoIIQ, which interacts with the mother cell protein SpoIIIAH at the septum to localize other sporulation proteins. It has remained unclear how SpoIIQ localizes. We demonstrate that localization of SpoIIQ is achieved by two pathways: SpoIIIAH and the SpoIID, SpoIIM, SpoIIP engulfment proteins. SpoIIQ shows diffuse localization only in a mutant lacking both pathways. Super-resolution imaging shows that in the absence of SpoIIIAH, SpoIIQ forms fewer, slightly larger foci than in wild type. Surprisingly, photobleaching experiments demonstrate that, although SpoIIQ localizes without SpoIIIAH, it is no longer immobilized, and is therefore able to exchange subunits within a localized pool. SpoIIQ mobility is further increased by the additional absence of the engulfment proteins. However an enzymatically inactive SpoIID protein immobilizes SpoIIQ even in the absence of SpoIIIAH, indicating that complete septal thinning is not required for SpoIIQ localization. This suggests that SpoIIQ interacts with both SpoIIIAH and the engulfment proteins or their peptidoglycan cleavage products. They further demonstrate that apparently normal localization of a protein without a binding partner can mask dramatic alterations in protein mobility. We speculate that SpoIIQ assembles foci along the path defined by engulfment proteins degrading peptidoglycan.

The SpoIIQ‐SpoIIIAH complex of Clostridium difficile controls forespore engulfment and late stages of gene expression and spore morphogenesis

“…Therefore, although SpoIIQ and SpoIIIAH are largely co‐dependent for localization, some SpoIIIAH can localize to asymmetric septa and the engulfing membranes independently of SpoIIQ. This contrasts with the situation in B. subtilis , where the localization of SpoIIIAH is dependent on SpoIIQ, but SpoIIQ localizes in the absence of SpoIIIAH (Rubio and Pogliano, ; Rodrigues et al ., ; Fredlund et al ., ). It suggests that in addition to SpoIIQ, tethering of SpoIIIAH at the septum and engulfing membranes involves additional factors.…”

“…SpoIIIAH and SpoIIQ localize to the asymmetric septum and to the engulfing membranes, and the two proteins interact in the intermembrane space via their extracytoplasmic domains Blaylock et al, 2004;Doan et al, 2005;. This interaction localizes SpoIIIAH to the septum and to the engulfing membranes but the primary tether for SpoIIQ, although dependent on mother cell gene expression, is still unclear (Blaylock et al, 2004;Rubio and Pogliano, 2004;Fredlund et al, 2013;Rodrigues et al, 2013). SpoIIQ and SpoIIIAH are thought to form a scaffold for the assembly of a larger complex that includes the remaining spoIIIA-encoded proteins Doan et al, 2009).…”

Diverse mechanisms regulate sporulation sigma factor activity in the Firmicutes

“…By thinning the peptidoglycan layer of the polar septum, the complex permits the assembly of a channel composed of components controlled by both forespore-specific σ F and mother cell-specific σ E [24,25]. This channel, consisting of SpoIIQ (σ F -controlled) and SpoIIIAA-AH (σ E -controlled), also known as the ‘feeding tube’, bridges the mother cell and forespore compartments and is necessary for σ G activation in the forespore [26–28].…”

Optical and force nanoscopy in microbiology

“…Cell envelopes play essential roles, such as defining cell shape and division, resisting turgor pressure, providing receptor sites for viruses and antibiotics, and controlling cell adhesion and biofilm formation. At this level, optical nanoscopy continues to enable the mapping of unique membrane distribution patterns and dynamics of a variety of membrane proteins, including chemotaxis receptors 111 , sporulation complexes 112 , toxins 113 , respiratory systems 114 and surface sugar metabolizing complexes 115 , and helped elucidate possible mechanisms of how a membrane protein’s localization and dynamics are coupled to its biological function. Yet here, force nanoscopy offers unique advantages over optical nanoscopy in probing structural and biophysical properties of cell surfaces with unmatched spatiotemporal resolution.…”