PORIN FROM KLEBSIELLA-PNEUMONIAE - SEQUENCE HOMOLOGY, 3-DIMENSIONAL MODEL, AND COMPLEMENT BINDING

A recombinant plasmid containing ompK36, the gene coding for the Klebs iella pneumoniae outer membrane protein OmpK36, was constructed by tra nsposon mutagenesis and subcloning. Clones were identified in a cosmid library in Escherichia coil on the basis of their reaction with antis erum against the OmpK36 protein and by the presence in gel electrophor etic analysis of a band in E. coli outer membranes migrating with a mo bility corresponding to 36 kDa, The ompK36-encoded protein exhibited c haracteristic properties of porins, such as heat modifiability and res istance to trypsin. The sequence of the gene revealed that OmpK36 is a close relative of the enterobacterial porin family, with a high degre e of homology with E. coli OmpC, PhoE, and OmpF. On the basis of the s tructures of OmpF and PhoE porins, determined previously by X-ray anal ysis, it appears likely that the three-dimensional structure of OmpK36 also contains the motif of a 16-stranded beta-barrel, with long loops on one end and short turns on the other. Like the OmpC porin from E. coli, OmpK36 contains a long insertion in loop 4. The results of a bin ding study of complement component Clq to OmpK36 and the analysis of t he OmpK36 model suggest that Clq binding sites are covered by the lipo polysaccharide core in the native porin.