hide
Free keywords:
-
Abstract:
The PII superfamily consists of widespread signal transduction proteins found in all domains of life. In addition to canonical PII proteins involved in C/N sensing, structurally similar PII-like proteins evolved to fulfill diverse, yet poorly understood cellular roles1. Cyanobacteria evolved highly specialized carbon concentrating mechanism (CCM) to cope with limiting atmospheric CO2 levels, augmenting intracellular inorganic carbon (Ci) levels to ensure efficient CO2-fixation2. The sodium-dependent bicarbonate transporter SbtA is highly expressed under Ci limitation together with the conserved PII-like SbtB protein3. SbtB can bind a variety of adenine nucleotides (ATP, ADP, AMP, and cAMP). The nucleotide-binding pocket was identified to be located between the subunit clefts of SbtB3, perfectly matching the structure of canonical PII proteins. Our previous results suggest that the novel PII-like protein SbtB acts as Ci sensor protein via integrating the energy state of the cell and cAMP binding3. The evolutionary conserved role of cAMP/AMP as an indicator of cellular carbon status is well understood3,4, but the function of ATP/ADP binding has remained unresolved. Here, we solved crystal structures of SbtB with ATP and ADP. Our structural and biochemical analysis revealed that SbtB has an ATPase activity. The slow ATPase activity of SbtB leads to a conformational change in the surface exposed T-loop of SbtB protein. We propose that the role of ATP/ADP binding is a molecular switch that drives a conformational change in the T-loops. We therefore suggest that the ATPase activity is likely to be a general property of most members of the PII superfamily5. However, the physiological role of the ATPase activity of SbtB remains obscure.
