Bacterial histidine kinases play an important role in the response to external Stimuli Structural studies of. the histidine kinase transmembrane domain are challenging due to difficulties in protein expression and sample preparation. After carrying out expression Screening of a series of histidine kinases, we investigated sample preparation methods for obtaining high quality samples of the periplasmic and transmembrane domain (PTD) of the bacterial histidine kinase SCO3062. Various sample conditions were tested for their ability to give homogeneous NMR spectra of the SCO3062 PTD with well-resolved resonances. Circular dichroism and 3D N-15-edited NOESY spectrum results demonstrate that the SCO3062 PTD is predominantly alpha-helical. This method should be applicable to the NMR analysis of other transmembrane proteins. (C) 2008 Elsevier Inc. All rights reserved.