Interhelical hydrogen bonds in the CFTR membrane domain

Critical mutations in the membrane-spanning domains of proteins cause many human diseases. We report the expression in Escherichia coli of helix-loop- helix segments of the cystic fibrosis transmembrane conductance regulator ( CFTR) chloride channel domain in milligram quantities. Analysis of gel migr ation patterns of these constructs, in conjunction with circular dichroism spectroscopy, demonstrate that a neutral-to-charged, CF-phenotypic point mu tation of a hydrophobic residue (V232D) in the CFTR transmembrane (TM) heli x 4 induces a hydrogen bond with neighboring wild type Gln 207 in TM helix 3. As an electrostatic crosslink within a hydrocarbon phase, such a hydroge n bond could alter the normal assembly and alignment of CFTR TM helices and /or impede their movement in response to substrate transport. Our results i mply that membrane proteins may be vulnerable to loss of function through f ormation of membrane-buried interhelical hydrogen bonds by partnering of pr oximal polar side chains.