Xenorhabdus luminescens HW is the only known luminous bacterium isolated from a human (wound) source. A recombinant plasmid was constructed that contained the X. luminescens HW luxA and luxB genes, encoding the luciferase a and j subunits, respectively, as well as luxC, luxD, and a portion of luxE. The nucleotide sequences of these lux genes, organized in the order luxCDABE, were determined, and overexpression of the cloned luciferase genes was achieved in Escherichia coli host cells. The cloned luciferase was indistinguishable from the wild-type enzyme in its in vitro bioluminescence kinetic properties. Contrary to an earlier report, our findings indicate'that neither the specific activity nor the size of the a (362 amino acid residues, Mr 41,389) and 1B(324 amino acid residues, M, 37,112) subunits of the X. luminescens HW luciferase was unusual among known luminous bacterial systems. Significant sequence homologies of the a and ,B subunits of the X. luminescens HW luciferase with those of other luminous bacteria were observed. However, the X. luminescens HW luciferase was unusual in the high stability of the 4a-hydroperoxyflavin intermediate and its sensitivity to aldehyde substrate inhibition.Most of the known luminous bacteria are of marine origin and fall within two genera, Vibrio and Photobacterium (references 13 and 23'and references therein). Luciferases from the marine bacteria Vibrio harveyi, Vibrio fischeri, Photobacterium leiognathi, and Photobacterium phosphoreum are all a1 heterodimers (14,19,25), with molecular weights of approximately 40,000 for a and 37,000 for P3. For the former three species, the luxA and luxB genes, encoding the luciferase a and P subunits, respectively, have been sequenced (4,9,15,17).A few nonmarine luminous bacterial species have also been identified (13, 23); among them are Xenorhabdus luminescens Hb and Hm, both of which are insect-pathogenic symbionts with nematodes of the family Heterorhabditidae (24,27,30). The luciferases from X. luminescens Hm and Hb have identical a subunits and only a single different amino acid residue in the P subunit. Moreover, they are similar in specific activity and subunit sizes to and have significant sequence homology with luciferases from marine luminous bacteria (16, 27, 29). The luxA and luxB genes from these two X. luminescens strains differ by only one and two bases, respectively (16,29). In fact, the known sequences of the lux operon, starting with the last 142 bases of luxD through the first four bases of luxE (with luxA, luxB, and noncoding regions in between) show 99% identity for X. luminescens Hm and Hb (16,29).A different luminous strain of X. luminescens has been isolated from a human wound (8), now designated strain HW. Some unusual properties have been reported for this strain and its luciferase (5) in comparison with all other known luminous bacteria, including X. luminescens Hm and Hb. X. luminescens HW bioluminescence activities both in vivo and in vitro have been found to be substantially lower in intensity but higher i...

The fluorescent alpha-parinaric acid (alpha-PAC) and beta-parinaric acid (beta-PAC) were converted to the corresponding aldehydes and alcohols all of which exhibited absorption and fluorescence properties closely resembling those of the parent acids. alpha-PAC and beta-PAC each binds to luciferase in competition with aldehyde. The hydrophobic nature of the aldehyde site was indicated by the enhanced fluorescence quantum yields of the bound alpha-PAC and beta-PAC. These two polyene acids and the beta-parinaryl alcohol were shown to stabilize the luciferase flavin-peroxide intermediate. alpha-Parinaraldehyde (alpha-PAD) and beta-parainaraldehyde (beta-PAD) were active substrates for Vibrio harveyi and Vibrio fischeri luciferases and, for the former enzyme, exhibited Km values similar to and quantum yields about 20-30% as those for decanal and dodecanal. For the V. harveyi luciferase with reduced FMN as a co-substrate, the alpha-PAD- or beta-PAD-initiated luminescence was indistinguishable from the normal emission obtained with octanal (lambda max 495 nm) showing no additional 430-nm component correlatable with emission from excited alpha-PAC or beta-PAC. In reactions using reduced 2-thioFMN for V. harveyi luciferase or reduced FMN for V. fischeri luciferase plus yellow fluorescent protein, the replacement of octanal by beta-PAD again resulted in no additional 430-nm emission. The lack of any emission correlatable with excited alpha-PAC, beta-PAC, or equivalent carbonyl product was not due to the quenching of the polyene moiety by chemical transformation, binding to luciferase, or a 100% energy transfer to the flavin 4a-hydroxide emitter.(ABSTRACT TRUNCATED AT 250 WORDS)