AtPng1p. The first plant transglutaminase.
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 gamma-glutamyl-derivatives revealed that the formation of covalent linkages between proteins and polyamines occurs via the transamidation of gamma-glutamyl residues of the substrate, confirming that the AtPng1p gene product acts as a TGase. The Ca(2+)- 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.
Dipartimento di Biologia Evoluzionistica Sperimentale, Università di Bologna, 40126 Bologna, Italy.
Massimiliano
M
Della Mea
David
D
Caparrós-Ruiz
Inmaculada
I
Claparols
Donatella
D
Serafini-Fracassini
Joan
J
Rigau
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000235:genetics; D001483:Base Sequence; D017931:DNA Primers; D005973:Glutamine / Q000378:metabolism; D006056:Golgi Apparatus / Q000201:enzymology; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013096:Spermine / Q000378:metabolism; D011503:Transglutaminases / Q000235:genetics*
D029681:Arabidopsis Proteins; D017931:DNA Primers; D005973:Glutamine; D013096:Spermine; D011503:Transglutaminases