The solution structure of the C-terminal domain of the Mu B transposition protein

Mu B is one of four proteins required for the strand transfer step of bacte riophage Mu DNA transposition and the only one where no high resolution str uctural data is available. Structural work on Mu B has been hampered primar ily by solubility problems and its tendency to aggregate. We have overcome this problem by determination of the three-dimensional structure of the C-t erminal domain of Mu B (B223-312) in 1.5 M NaCl using NMR spectroscopic met hods. The structure of Mu B223-312 comprises four helices (backbone r.m.s.d . 0.46 Angstrom) arranged in a loosely packed bundle and resembles that of the N-terminal region of the replication helicase, DnaB. This structural mo tif is likely to be involved in the inter-domainal regulation of ATPase act ivity for both Mu A and DnaB. The approach described here for structural de termination in high salt may be generally applicable for proteins that do n ot crystallize and that are plagued by solubility problems at low ionic str ength.