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Evolution of alpha 2-macroglobulin. The structure of a protein homologous with human alpha 2-macroglobulin from plaice (Pleuronectes platessa L.) plasma.

ABSTRACT: The plaice (Pleuronectes platessa L.) papain-binding protein previously demonstrated to be homologous with human alpha(2)-macroglobulin, and designated plaice alpha(2)-macroglobulin homologue or alphaMh, was shown to be a glycoprotein of s(20,w) 11.86S. In polyacrylamide-gel pore-limit electrophoresis under non-denaturing conditions plaice alphaMh migrated to the same position as half-molecules of human alpha(2)-macroglobulin, and treatment with methylamine or a proteinase caused no change in its electrophoretic properties. Either denaturation in urea (4m) or mild reduction by dithiothreitol (1mm) partially dissociated plaice alphaMh into half-molecules. Denaturation with reduction further dissociated the protein into quarter-subunits. In sodium dodecyl sulphate/polyacrylamide-gel electrophoresis under reducing conditions plaice alphaMh dissociated into subunits of M(r) 105000 (I) and 90000 (II). Approximately equal amounts of each subunit were formed, and peptide ;mapping' showed subunits I and II to be distinct polypeptide chains. Under alkaline denaturing conditions, a proportion of the I chains of alphaMh were cleaved into fragments of M(r) about 60000 and 40000. This cleavage was favoured by reducing conditions and prevented by prior inactivation of the alphaMh with methylamine. [(14)C]Methylamine allowed to react with alphaMh became covalently linked to subunit I. These properties suggested the existence of an autolytic site on subunit I analogous to the autolytic site of human alpha(2)-macroglobulin. Reaction of alphaMh with a proteinase resulted in cleavage of a fragment of M(r) 10000-15000 from subunit I. A proportion of the proteinase molecules trapped by alphaMh became covalently linked to the inhibitor. A scheme is proposed for the evolution of human alpha(2)-macroglobulin and plaice alphaMh from a common ancestral protein, which may also have been an ancestor of complement components C3 and C4.

SUBMITTER: Starkey PM

PROVIDER: S-EPMC1158452 | biostudies-other | 1982 Jul

REPOSITORIES: biostudies-other

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Project description:Similar to other marine holobionts, fish are colonized by complex microbial communities that promote their health and growth. Fish-associated microbiota is emerging as a promising source of bioactive metabolites. Pleuronectes platessa (European plaice, plaice), a flatfish with commercial importance, is common in the Baltic Sea. Here we used a culture-dependent survey followed by molecular identification to identify microbiota associated with the gills and the gastrointestinal tract (GIT) of P. platessa, then profiled their antimicrobial activity and metabolome. Altogether, 66 strains (59 bacteria and 7 fungi) were isolated, with Proteobacteria being the most abundant phylum. Gill-associated microbiota accounted for higher number of isolates and was dominated by the Proteobacteria (family Moraxellaceae) and Actinobacteria (family Nocardiaceae), whereas Gram-negative bacterial families Vibrionaceae and Shewanellaceae represented the largest group associated with the GIT. The EtOAc extracts of the solid and liquid media cultures of 21 bacteria and 2 fungi representing the diversity of cultivable plaice-associated microbiota was profiled for their antimicrobial activity against three fish pathogens, human bacterial pathogen panel (ESKAPE) and two human fungal pathogens. More than half of all tested microorganisms, particularly those originating from the GIT epithelium, exhibited antagonistic effect against fish pathogens (Lactococcus garvieae, Vibrio ichthyoenteri) and/or human pathogens (Enterococcus faecium, methicillin-resistant Staphylococcus aureus). Proteobacteria represented the most active isolates. Notably, the solid media extracts displayed higher activity against fish pathogens, while liquid culture extracts were more active against human pathogens. Untargeted metabolomics approach using feature-based molecular networking showed the high chemical diversity of the liquid extracts that contained undescribed clusters. This study highlights plaice-associated microbiota as a potential source of antimicrobials for the control of human and the aquaculture-associated infections. This is the first study reporting diversity, bioactivity and chemical profile of culture-dependent microbiota of plaice.

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Evolution of alpha 2-macroglobulin. The structure of a protein homologous with human alpha 2-macroglobulin from plaice (Pleuronectes platessa L.) plasma.

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