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Non-covalent interactions result in aggregation of surface antigens of the parasitic nematode Trichinella spiralis.

ABSTRACT: Surface antigens of three stages of the nematode worm Trichinella spiralis has been labelled with iodine and examined by sodium dodecyl sulphate (SDS)/polyacrylamide-gel electrophoresis under reducing and non-reducing conditions. A variety of interactions were defined: the infective larva surface antigens formed a spectrum of aggregates from 50kDa to greater than 1000kDa from subunits of 47kDa and 90kDa; in the adult worms of 60kDa complex arose fron interaction between two dissimilar molecules of 40kDa and 20kDa; the new-born larvae components formed homologous dimers from a 58kDa molecule. Aggregating molecules were adherent to lentil lectin-Sepharose and are therefore glycoproteins. The interactions observed were completely abolished by boiling in SDS/mercaptoethanol, but only partially destroyed by boiling in SDS/iodoacetamide. Based upon this, the associations can be characterized as non-covalent, but disulphide-bond-dependent. It is suggested, but not proved, that the aggregates arise from strong non-covalent hydrophobic interaction sites which are stabilized by intrachain disulphide bonds in the molecules concerned.

SUBMITTER: Clark NW

PROVIDER: S-EPMC1158545 | biostudies-other | 1982 Jul

REPOSITORIES: biostudies-other

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Project description:cDNAs were obtained for macrophage migration-inhibitory factor (MIF)/L-dopachrome methyl ester tautomerase homologues from the parasitic nematodes Trichinella spiralis (TsMIF) and Trichuris trichiura (TtMIF). The translated sequences, which were partly confirmed by sequencing of proteolytic fragments, show 42 and 44% identity respectively with human or mouse MIF, and are shorter by one C-terminal residue. Unlike vertebrate MIF and MIF homologues of filarial nematodes, neither TsMIF nor TtMIF contain cysteine residues. Soluble recombinant TsMIF, expressed in Escherichia coli showed secondary structure (by CD spectroscopy) and quaternary structure (by light-scattering and gel filtration) similar to that of the trimeric mammalian MIFs and D-dopachrome tautomerase. The catalytic specificity of recombinant TsMIF in the ketonization of phenylpyruvate (1.4x10(6) M(-1) x s(-1)) was comparable with that of human MIF, while that of p-hydroxyphenylpyruvate (9.1x10(4) M(-1) x s(-1)) was 71-fold lower. TsMIF showed high specificity in tautomerization of the methyl ester of L-dopachrome compared with non-esterified L-dopachrome (>87000-fold) and a high kcat (approximately 4x10(4) s(-1). The crystal structure, determined to 1.65 A (1 A=0.1 nm), was generally similar to that of human MIF, but differed in the boundaries of the putative active-site pocket, which can explain the low activity towards p-hydroxyphenylpyruvate. The central pore was blocked, but was continuous, with the three putative tautomerase sites. Recombinant TsMIF (5 ng/ml-5 pg/ml) inhibited migration of human peripheral-blood mononuclear cells in a manner similar to that shown by human MIF, but had no effect from 5 to 500 ng/ml on anti-CD3-stimulated murine T-cell proliferation. TsMIF was detected in supernatants of T. spiralis larvae cultured in vitro at 6 ng/ml (55 ng/mg total secreted protein). In conclusion TsMIF has structural, catalytic and cell-migration-inhibitory properties which indicate that it is partially orthologous to mammalian MIF.

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Non-covalent interactions result in aggregation of surface antigens of the parasitic nematode Trichinella spiralis.

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