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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

AtPng1p. The First Plant Transglutaminase^1,[w]

Dipartimento di Biologia Evoluzionistica Sperimentale, Università di Bologna, 40126 Bologna, Italy (M.D.M., D.S.-F.); and Consorci CSIC-IRTA Laboratori de Genètica Molecular Vegetal, Jordi Girona 18-26, 08034 Barcelona, Spain (D.C.-R., I.C., J.R.)

Studies have revealed in plant chloroplasts, mitochondria, cell walls, and cytoplasm the existence of transglutaminase (TGase) activities, similar to those known in animals and prokaryotes having mainly structural roles, but no protein has been associated to this type of activity in plants. A recent computational analysis has shown in Arabidopsis the presence of a gene, AtPng1p, which encodes a putative N-glycanase. AtPng1p contains the Cys-His-Asp triad present in the TGase catalytic domain. AtPng1p is a single gene expressed ubiquitously in the plant but at low levels in all light-assayed conditions. The recombinant AtPng1p protein could be immuno-detected using animal TGase antibodies. Furthermore, western-blot analysis using antibodies raised against the recombinant AtPng1p protein have lead to its detection in microsomal fraction. The purified protein links polyamines—spermine (Spm) > spermidine (Spd) > putrescine (Put)—and biotin-cadaverine to dimethylcasein in a calcium-dependent manner. Analyses of the -glutamyl-derivatives revealed that the formation of covalent linkages between proteins and polyamines occurs via the transamidation of -glutamyl residues of the substrate, confirming that the AtPng1p gene product acts as a TGase. The Ca²⁺- and GTP-dependent cross-linking activity of the AtPng1p protein can be visualized by the polymerization of bovine serum albumine, obtained, like the commercial TGase, at basic pH and in the presence of dithiotreitol. To our knowledge, this is the first reported plant protein, characterized at molecular level, showing TGase activity, as all its parameters analyzed so far agree with those typically exhibited by the animal TGases.

² These authors contributed equally to the paper.

^[w] The online version of this article contains Web-only data.

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.104.042549.

^* Corresponding author; e-mail donatella.serafini{at}unibo.it; fax 39–051242576.

Received March 12, 2004; returned for revision April 30, 2004; accepted May 11, 2004.

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