Replacement of the Sole Histidinyl Residue in OmpF Porin from E. Coli by Threonine (H21T) Does Not Affect Channel Structure and Function

The sole histidine residue in OmpF porin was replaced by threonine using site-directed mutagenesis. This exchange affected neither channel properties nor channel structure, as determined by X-ray analysis to 3.2 A. Conductance and critical voltage (Vc) were observed in the pH range 4.3-9.4, with results indistinguishable from those observed in the wild-type protein. The validity of these observations is supported by the independence of the methods used, and by the fact that mutants in residues located in the channel constriction yielded significantly different values from wild-type protein. The binding of a glycolipid molecule might be affected.