REPLACEMENT OF THE SOLE HISTIDINYL RESIDUE IN OMPF PORIN FROM ESCHERICHIA-COLI BY THREONINE (H21T) DOES NOT AFFECT CHANNEL STRUCTURE AND FUNCTION

The sole histidine residue in OmpF porin was replaced by threonine usi ng site-directed mutagenesis. This exchange affected neither channel p roperties nor channel structure, as determined by X-ray analysis to 3. 2 Angstrom. Conductance and critical voltage (V-c) were observed in th e pH range 4.3-9.4, with results indistinguishable from those observed in the wild-type protein. The validity of these observations is suppo rted by the independence of the methods used, and by the fact that mut ants in residues located in the channel constriction yielded significa ntly different values from wild-type protein. The binding of a glycoli pid molecule might be affected. (C) 1996 Academic Press, Inc.