Plant and animal transglutaminases: do similar functions imply similar structures?

In plants the post-translational modification of proteins by polyamines catalysed by transglutaminases has been studied since ’87: it was identified by the production of glutamyl-polyamine derivatives, biochemical features, recognition by animal antibodies and modification of typical animal substrates. Transglutaminases are widespread in all plant organs and cell compartments studied until now, chloroplast being the most studied. Substrates are: photosynthetic complexes and Rubisco in chloroplasts, cytoskeleton and cell wall proteins. Roles either specific of plants or in common with animals are related to photosynthesis, fertilisation, stresses, senescence and programmed cell death, showing that the catalytic function is conserved across the kingdoms. AtPng1p, the first plant transglutaminase sequenced shows undetectable sequence homology with the animal enzymes, except for the catalytic triad. It is however endowed with a calcium dependent activity that allowed us to build a three dimensional model adopting as a template the animal tranglutaminase 2.