STRUCTURAL AND FUNCTIONAL-CHARACTERIZATION OF OMPF PORIN MUTANTS SELECTED FOR LARGER PORE-SIZE .1. CRYSTALLOGRAPHIC ANALYSIS

OmpF porin is a nonspecific pore protein from the outer membrane of Es cherichia coli. Previously, a set of mutants was selected that allow t he passage of long maltodextrins that do not translocate through the w ild-type pore. Here, we describe the crystal structures of four point mutants and one deletion mutant from this set; their functional charac terization is reported in the accompanying paper (Saint, N,, Leu, K.-L ., Widmer, C,, Luckey, M., Schirmer, T,, Rosenbusch, J, P, (1996) J, B iol. Chem. 271, 20676-20680), All mutations have a local effect on the structure of the pore constriction and result in a larger pore cross- section, Substitution of each of the three closely packed arginine res idues at the pore constriction (Arg-42, Arg-82, and Arg-132) by shorte r uncharged residues causes rearrangement of the adjacent basic residu es, This demonstrates mutual stabilization of these residues in the wi ld-type porin, Deletion of six residues from the internal loop (Delta 109-114) results in disorder of seven adjacent residues but does not a lter the structure of the beta-barrel framework, Thus, the large hollo w beta-barrel motif can be regarded as an autonomous structure.