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Type III metacaspases: calcium‐dependent activity proposes new function for the p10 domain
Author(s) -
Klemenčič Marina,
Funk Christiane
Publication year - 2018
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/nph.14660
Subject(s) - biochemistry , chemistry , enzyme , endopeptidase , calcium , active site , biology , organic chemistry
Summary Metacaspases are a subgroup of caspase homologues represented in bacteria, algae and plants. Although type I and type II metacaspases are present in plants, recently discovered and uncharacterized type III metacaspases can only be found in algae which have undergone secondary endosymbiosis. We analysed the expression levels of all 13 caspase homologues in the cryptophyte Guillardia theta in vivo and biochemically characterized its only type III metacaspase, Gt MC 2, in vitro . Type III metacaspase Gt MC 2 was shown to be an endopeptidase with a preference for basic amino acids in the P1 position, which exhibited specific N‐terminal proteolytic cleavage for full catalytic efficiency. Autolytic processing, as well as the activity of the mature enzyme, required the presence of calcium ions in low millimolar concentrations. In Gt MC 2, two calcium‐binding sites were identified, one with a dissociation constant at low and the other at high micromolar concentrations. We show high functional relatedness of type III metacaspases to type I metacaspases. Moreover, our data suggest that the low‐affinity calcium‐binding site is located in the p10 domain, which contains a well‐conserved N‐terminal region. This region can only be found in type I/II/III metacaspases, but is absent in calcium‐independent caspase homologues.