Inorganic polyphosphate (polyP) is widely recognized for playing important roles and processes involved in energy and phosphate storage, regulation of gene expression, and calcium signaling. The less well-known role of polyP is as a direct mediator of ion transport across biological membranes. Here, we will briefly summarize current knowledge of the molecular mechanisms of how polyP can be involved in membrane ion transport. We discuss three types of mechanisms that might involve polyP: (1) formation of non-protein channel complex that includes calcium, polyP, and polyhydroxybutyrate (PHB); (2) modulation of the channel activity of PHBlated protein channels; and (3) direct effects of polyP on the function of the voltage-gated ion channels in the process that do not involve PHB.
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Cover Image
Cover Image
Single-molecule imaging techniques have revealed the dynamic nature of ion channels and shown that channel activity is sometimes dependent on their mobility and mechanical forces in the lipid membrane. The cover image shows a recent high-resolution cryo-EM image of the two-pore structure of the core complex of the mitochondrial outer membrane protein translocase (TOM) from the filamentous fungus
Neurospora crassa , together with a single-molecule false-color image illustrating the calcium flux through its two pores associated with conformational changes of this protein complex. The TOM core complex undergoes reversible transitions between active (high intensity pink dots), weakly active (medium intensity pink dots) and inactive (low intensity pink dots) channel states corresponding to the suspension of movement. For more information, see the article by Nussberger and colleagues (pp. 911–922) in this issue. Image provided by Shuo Wang.
Inorganic polyphosphate and ion transport across biological membranes
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