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Orthocaspases are proteolytically active prokaryotic caspase homologues: the case of M icrocystis aeruginosa
Author(s) -
Klemenčič Marina,
Novinec Marko,
Dolinar Marko
Publication year - 2015
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/mmi.13110
Subject(s) - biology , microbiology and biotechnology , computational biology
Summary Caspases are a family of cysteine‐dependent proteases known to be involved in the process of programmed cell death in metazoans. Recently, cyanobacteria were also found to contain caspase‐like proteins, but their existence has only been identified in silico up to now. Here, we present the first experimental characterisation of a prokaryotic caspase homologue. We have expressed the putative caspase‐like gene MaOC 1 from the toxic bloom‐forming cyanobacterium M icrocystis aeruginosa PCC 7806 in E scherichia coli . Kinetic characterisation showed that MaOC 1 is an endopeptidase with a preference for arginine in the P 1 position and a pH optimum of 7.5. MaOC 1 exhibited high catalytic rates with the k cat / K M value for Z‐RR‐AMC substrate of the order 10 6 M −1 s −1 . In contrast to plant or metazoan caspase‐like proteins, whose activity is calcium‐dependent or requires dimerisation for activation, MaOC 1 was activated by autocatalytic processing after residue A rg219, which separated the catalytic domain and the remaining 55 kDa subunit. The A rg219 A la mutant was resistant to autoprocessing and exhibited no proteolytic activity, confirming that processing of MaOC 1 is a prerequisite for its activity. Due to their structural and functional differences to other known caspase‐like proteins, we suggest to name these evolutionary primitive proteins orthocaspases.