Abstract
Random mutations and selective pressure drive protein adaptation to the changing demands of the environment. As a consequence, nature favors the evolution of protein diversity. A group of proteins subject to exceptional environmental stress and known for their widespread diversity are the pore-forming hemolytic proteins from sea anemones, known as actinoporins. In this study, we identified and isolated new isoforms of actinoporins from the sea anemone Actinia fragacea (fragaceatoxins). We characterized their hemolytic activity, examined their stability and structure, and performed a comparative analysis of their primary sequence. Sequence alignment reveals that most of the variability among actinoporins is associated with non-functional residues. The differences in the thermal behavior among fragaceatoxins suggest that these variability sites contribute to changes in protein stability. In addition, the protein–protein interaction region showed a very high degree of identity (92%) within fragaceatoxins, but only 25% among all actinoporins examined, suggesting some degree of specificity at the species level. Our findings support the mechanism of evolutionary adaptation in actinoporins and reflect common pathways conducive to protein variability.
Highlights
Protein toxins have diversified through evolution to acquire specialized functions such as predation, defense, and digestion [1,2,3,4]
After the identification and isolation of a new actinoporin from the sea anemone Actinia fragacea [22], we studied the applicability of this concept to actinoporins and made a comparative analysis at the single-residue level
Five actinoporins from Actinia fragacea were purified as described in Materials and Methods
Summary
Protein toxins have diversified through evolution to acquire specialized functions such as predation, defense, and digestion [1,2,3,4]. This diversification is the result of different kinds of evolutionary adaptation. Toxins 2019, 11, 401 favors the rapid segregation of new phenotypes [5,6]. Others, such as cnidarian pore-forming toxins, are mostly influenced by negative (purifying) selection where proteins retain functionally important regions [7], leading to a wide distribution of highly similar protein species. Influenced by negative selection [3,7], actinoporins have conserved important functional sites to ensure the preservation of their mechanism of pore formation, a complex process involving many different steps [9,10]
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