FUNCTIONAL AND REGULATORY ANALYSIS OF THE OMPF-LIKE PORIN, OPNP, OF THE SYMBIOTIC BACTERIUM XENORHABDUS-NEMATOPHILUS

The function and novel regulation of OpnP of the symbiotic/pathogenic bacterium, Xenorhabdus nematophilus was studied. In vitro pore-functio n analysis of purified OpnP indicated that the single-channel-conducta nce values were similar to that measured for the porin protein, OmpF, of Esherichia coli. Nucleotide sequence analysis revealed that the mat ure OpnP protein contained 348 amino acid residues and shared 55% amin o acid sequence identity with OmpF. Similar to ompF, opnP mapped betwe en asnS and aspC. The 16 transmembrane beta-sheet structures and the i nternal loop 3 were highly conserved, while the remaining external loo p domains were more divergent. Primer extension analysis identified th e start site of transcription of opnP. A sigma(70)-type promoter, a pe rfect 20 bp OmpR-binding site, and a binding site for the antisense mo lecule, micF RNA, were found in the upstream region of opnP. While the overall sequence identity of the asn-opnP-aspC region was high, the i ntergenic region between asnS and opnP had diverged markedly. The asnS -opnP region was 313 bp shorter than the intergenic region between asn S and ompF and lacked the OmpR-binding site that is required for ompF repression by high osmolarity in E. coli. Results from osmolarity-shif t experiments indicated that OpnP was not repressed by high osmolarity . It was also found that OpnP was thermally regulated.