Characterization of the molecular properties of KtrC, a second RCK domain that regulates a Ktr channel in Bacillus subtilis

• Autor(a) principal: Rocha, R
• Data de Publicação: 2019
• Outros Autores: Teixeira-Duarte, CM, JMP, J, Morais-Cabral, JH
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: https://hdl.handle.net/10216/127799
• topic: Adenosine Diphosphate / chemistry; Adenosine Diphosphate / metabolism; Adenosine Triphosphate / chemistry; Adenosine Triphosphate / metabolism; Amino Acid Motifs; Bacillus subtilis / chemistry; Bacillus subtilis / metabolism; Bacterial Proteins / chemistry; Bacterial Proteins / genetics; Bacterial Proteins / metabolism; Binding Sites; Cation Transport Proteins / chemistry; Cation Transport Proteins / genetics; Cation Transport Proteins / metabolism; Cations, Monovalent; Cloning, Molecular; Crystallography, X-Ray; Dinucleoside Phosphates / chemistry; Dinucleoside Phosphates / metabolism; Escherichia coli / genetics; Escherichia coli / metabolism; Gene Expression; Genetic Complementation Test; Genetic Vectors / chemistry; Genetic Vectors / metabolism; Ion Transport; Models, Molecular; Potassium / chemistry; Potassium / metabolism; Protein Binding; Protein Conformation, alpha-Helical; Protein Conformation, beta-Strand; Protein Interaction Domains and Motifs; Protein Isoforms / chemistry; Protein Isoforms / genetics; Protein Isoforms / metabolism; Protein Multimerization; Recombinant Proteins / chemistry; Recombinant Proteins / genetics; Recombinant Proteins / metabolism

RCK (regulating conductance of K+) domains are common regulatory domains that control the activity of eukaryotic and prokaryotic K+ channels and transporters. In bacteria these domains play roles in osmoregulation, regulation of turgor and membrane potential and in pH homeostasis. Whole-genome sequencing unveiled RCK gene redundancy, however the biological role of this redundancy is not well understood. In Bacillus subtilis, there are two closely related RCK domain proteins (KtrA and KtrC) that regulate the activity of the Ktr cation channels. KtrA has been well characterized but little is known about KtrC. We have characterized the structural and biochemical proprieties of KtrC and conclude that KtrC binds ATP and ADP, just like KtrA. However, in solution KtrC exist in a dynamic equilibrium between octamers and non-octameric species that is dependent on the bound ligand, with ATP destabilizing the octameric ring relative to ADP. Accordingly, KtrC-ADP crystal structures reveal closed octameric rings similar to those in KtrA, while KtrC-ATP adopts an open assembly with RCK domains forming a super-helix. In addition, both KtrC-ATP and -ADP octamers are stabilized by the signaling molecule cyclic-di-AMP, which binds to KtrC with high affinity. In contrast, c-di-AMP binds with 100-fold lower affinity to KtrA. Despite these differences we show with an E. coli complementation assay that KtrC and KtrA are interchangeable and able to form functional transporters with both KtrB and KtrD. The distinctive properties of KtrC, in particular ligand-dependent assembly/disassembly, suggest that this protein has a specific physiological role that is distinct from KtrA.