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Crystal structure and biochemical analyses reveal that the A rabidopsis triphosphate tunnel metalloenzyme A t TTM 3 is a tripolyphosphatase involved in root development
Author(s) -
Moeder Wolfgang,
GarciaPetit Christel,
Ung Huoi,
Fucile Geoffrey,
Samuel Marcus A.,
Christendat Dinesh,
Yoshioka Keiko
Publication year - 2013
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/tpj.12325
Subject(s) - arabidopsis , biochemistry , arabidopsis thaliana , cyclase , biology , chemistry , enzyme , mutant , gene
Summary The A rabidopsis protein A t TTM 3 belongs to the CYTH superfamily named after its two founding members, the C ya B adenylate cyclase from A eromonas hydrophila and the mammalian thiamine triphosphatase. In this study we report the three‐dimensional structure of a plant CYTH domain protein, A t TTM 3, determined at 1.9 Å resolution. The crystal structure revealed the characteristic tunnel architecture of CYTH proteins, which specialize in the binding of nucleotides and other organic phosphates and in phosphoryl transfer reactions. The β barrel is composed of eight antiparallel β strands with a cluster of conserved inwardly facing acidic and basic amino acid residues. Mutagenesis of these residues in the catalytic core led to an almost complete loss of enzymatic activity. We established that A t TTM 3 is not an adenylate cyclase. Instead, the enzyme displayed weak NTP phosphatase as well as strong tripolyphosphatase activities similar to the triphosphate tunnel metalloenzyme proteins from C lostridium thermocellum ( C th TTM ) and N itrosomonas europaea ( N eu TTM ). A t TTM 3 is most highly expressed in the proximal meristematic zone of the plant root. Furthermore, an A t TTM 3 T ‐ DNA insertion knockout line displayed a delay in root growth as well as reduced length and number of lateral roots, suggesting a role for A t TTM 3 in root development.