Protein splicing and tryptophan fluorescence of salt‐dependent inteins from Haloquadratum walsbyi

Protein splicing is a self‐catalyzed reaction by which an intein, an intervening polypeptide, catalyzes its own removal from exteins, the flanking polypeptides, as well as ligation of the exteins. We are studying the inteins that interrupt a cell division control protein in the halophilic archaea Haloquadratum walsbyi. Halophiles like H. walsbyi are able to survive in water with high concentrations of sodium chloride. H. walsbyi has four inteins that interrupt the cdc21 gene, and we have studied the two inteins (Hwa cdc21A and Hwa cdc21D) that lack an intervening homing endonuclease domain. We are studying the splicing activity under various salt concentrations for the inteins both separately and when expressed as part of a single fusion protein. Hwa cdc21A splices optimally at 2.5 M NaCl, while Hwa cdc21D splices optimally at 1.5 M NaCl. We also are using native Trp fluorescence to study the influence of salt concentration on the proper folding of the inteins. Support or Funding Information This work was supported by NSF grant MCB‐1517138, a Henry Dreyfus Teacher‐Scholar Award, and NIH Grant 1R15GM132817‐01.