Biochemical study of sortase E2 from Streptomyces mobaraensis and determination of transglutaminase cross-linking sites

The metal-binding properties of the long chaplin from Streptomyces mobaraensis: A bioinformatic and biochemical approach

Chaplins are amphiphilic proteins coating the surface of aerial hyphae under formation of amyloid-like rodlet layers in streptomycetes. The long chaplin from Streptomyces mobaraensis, Sm-Chp1, harbors extended histidine-rich stretches allowing protein attachment to metal affinity resins. A comprehensive BLASTP search revealed similarity with many putative metal-binding proteins but the deduced sequence motifs were not shared by histidine-rich domains of well-studied proteins. Biochemical analyses showed affinity of Sm-Chp1 for Ni²⁺, Cu²⁺ and Zn²⁺, a binding capacity of 7-8 metal ions, and dissociation constants in a double digit micromolar range. The occurrence of genes for membrane-bound metal transporters and several intra- and extracellular metalloenzymes in the genome of S. mobaraensis suggests that Sm-Chp1 may be a novel type of translocase shifting metals across the rodlet layer from the environment into the cell wall.