SEQUENCE, EXPRESSION AND EVOLUTION OF THE GLOBINS OF THE PARASITIC NEMATODE NIPPOSTRONGYLUS-BRASILIENSIS

The globins of the nematode parasite Nippostrongylus brasiliensis have oxygen affinities 100-fold higher than the rodent host's haemoglobins . Two isoforms are found, one located in the cuticle, and the other in the body of the nematode. Both isoforms have been cloned and analysed for clues as to function and evolution. The body globin isoform is fi rst expressed upon invasion of the mammalian host. The abundant cuticu lar globin is expressed only by adult nematodes in the gut, and differ s significantly from the body globin. Both globins are found as trans- spliced mRNAs: the development pattern of expression of the mRNA paral lels the protein expression. The pattern of evolution of the nematode globin genes is complex. Comparison with other nematode globin sequenc es suggest that N. brasiliensis is more closely related to Caenorhabdi tis elegans than to ascarid species. At least two gene duplication eve nts are predicted: gene duplication preceded the radiation of the impo rtant vertebrate-parasitic strongylid nematode species. Both N. brasil iensis globins have a central intron the exact position of which sugge sts that it arose from an independent insertion event in the strongyli d-rhabditid line. The globins have been expressed in Escherichia coli as functional holoenzymes as a prelude to studies to elucidate the ori gin of their extraordinary oxygen affinity.