Three-dimensional model for the membrane domain of Escherichia coli leader peptidase based on disulfide mapping

We have mapped the interface between the two transmembrane alpha-helices in the membrane domain of the Escherichia coli enzyme leader peptidase by analyzing disulfides formed between pairs of cysteine residues introduced near their respective periplasmic ends. The interface is formed primarily from aliphatic amino acids, and the two helices appear to pack against each other in a left-handed supercoil. We suggest that disulfide mapping may be a generally applicable approach for the construction of models of helix-helix interfaces in membrane proteins.