AOBPreview originally published online on May 20, 2008
Annals of Botany 2008 102(2):145-152; doi:10.1093/aob/mcn075
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BOTANICAL BRIEFING |
Transglutaminases: Widespread Cross-linking Enzymes in Plants
Dipartimento di Biologia evoluzionistica sperimentale University of Bologna, Via Irnerio 42, 40126 Bologna, Italy
* For correspondence. E-mail donatella.serafini{at}unibo.it
Received: 17 January 2008 Returned for revision: 19 February 2008 Accepted: 14 April 2008 Published electronically: 20 May 2008
Background: Transglutaminases have been studied in plants since 1987 in investigations aimed at interpreting some of the molecular mechanisms by which polyamines affect growth and differentiation. Transglutaminases are a widely distributed enzyme family catalysing a myriad of biological reactions in animals. In plants, the post-translational modification of proteins by polyamines forming inter- or intra-molecular cross-links has been the main transglutaminase reaction studied.
Characteristics of Plant Transglutaminases: The few plant transglutaminases sequenced so far have little sequence homology with the best-known animal enzymes, except for the catalytic triad; however, they share a possible structural homology. Proofs of their catalytic activity are: (a) their ability to produce glutamyl-polyamine derivatives; (b) their recognition by animal transglutaminase antibodies; and (c) biochemical features such as calcium-dependency, etc. However, many of their fundamental biochemical and physiological properties still remain elusive.
Transglutaminase Activity is Ubiquitous: It has been detected in algae and in angiosperms in different organs and sub-cellular compartments, chloroplasts being the best-studied organelles.
Possible Roles: Possible roles concern the structural modification of specific protein substrates. In chloroplasts, transglutaminases appear to stabilize the photosynthetic complexes and Rubisco, being regulated by light and other factors, and possibly exerting a positive effect on photosynthesis and photo-protection. In the cytosol, they modify cytoskeletal proteins. Preliminary reports suggest an involvement in the cell wall construction/organization. Other roles appear to be related to fertilization, abiotic and biotic stresses, senescence and programmed cell death, including the hypersensitive reaction.
Conclusions: The widespread occurrence of transglutaminases activity in all organs and cell compartments studied suggests a relevance for their still incompletely defined physiological roles. At present, it is not possible to classify this enzyme family in plants owing to the scarcity of information on genes encoding them.
Key words: Transglutaminases, polyamines, cross-links, chloroplast, light-dependence, cell wall, stress, programmed cell death, monocotyledons, dicotyledons, algae
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