Proteins with CHADs (Conserved Histidine α-Helical Domains) Are Attached to Polyphosphate Granules and Constitute a Novel Family of Polyphosphate-Associated Proteins (Phosins).

On the basis of bioinformatic evidence, we suspected that proteins with a CYTH (aB iamine triphosphatase) domain and/or a CHAD (onserved istidine -helical omain) motif might represent polyphosphate (polyP) granule-associated proteins. We found no evidence of polyP targeting by proteins with CYTH domains. In contrast, two CHAD motif-containing proteins from H16 (A0104 and B1017) that were expressed as fusions with enhanced yellow fluorescent protein (eYFP) colocalized with polyP granules.

Formation of polyphosphate by polyphosphate kinases and its relationship to poly(3-hydroxybutyrate) accumulation in Ralstonia eutropha strain H16.

A protein (PhaX) that interacted with poly(3-hydroxybutyrate) (PHB) depolymerase PhaZa1 and with PHB granule-associated phasin protein PhaP2 was identified by two-hybrid analysis. Deletion of phaX resulted in an increase in the level of polyphosphate (polyP) granule formation and in impairment of PHB utilization in nutrient broth-gluconate cultures. A procedure for enrichment of polyP granules from cell extracts was developed.