title: Functional characterization of Arabidopsis thaliana transthyretin-like protein.
abstract: BACKGROUND
  Arabidopsis thaliana transthyretin-like (TTL) protein is a potential substrate in the brassinosteroid signalling cascade, having a role that moderates plant growth. Moreover, sequence homology revealed two sequence domains similar to 2-oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline (OHCU) decarboxylase (N-terminal domain) and 5-hydroxyisourate (5-HIU) hydrolase (C-terminal domain). TTL is a member of the transthyretin-related protein family (TRP), which comprises a number of proteins with sequence homology to transthyretin (TTR) and the characteristic C-terminal sequence motif Tyr-Arg-Gly-Ser. TRPs are single domain proteins that form tetrameric structures with 5-HIU hydrolase activity. Experimental evidence is fundamental for knowing if TTL is a tetrameric protein, formed by the association of the 5-HIU hydrolase domains and, in this case, if the structural arrangement allows for OHCU decarboxylase activity. This work reports about the biochemical and functional characterization of TTL.
  
  
  RESULTS
  The TTL gene was cloned and the protein expressed and purified for biochemical and functional characterization. The results show that TTL is composed of four subunits, with a moderately elongated shape. We also found evidence for 5-HIU hydrolase and OHCU decarboxylase activities in vitro, in the full-length protein.
  
  
  CONCLUSIONS
  The Arabidopsis thaliana transthyretin-like (TTL) protein is a tetrameric bifunctional enzyme, since it has 5-HIU hydrolase and OHCU decarboxylase activities, which were simultaneously observed in vitro.
authors.affiliation: IBMC - Instituto de Biologia Molecular e Celular, Universidade do Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal.
authors.forename: João
authors.initials: J
authors.lastname: Pessoa
authors.forename: Zsuzsa
authors.initials: Z
authors.lastname: Sárkány
authors.forename: Frederico
authors.initials: F
authors.lastname: Ferreira-da-Silva
authors.forename: Sónia
authors.initials: S
authors.lastname: Martins
authors.forename: Maria R
authors.initials: MR
authors.lastname: Almeida
authors.forename: Jianming
authors.initials: J
authors.lastname: Li
authors.forename: Ana M
authors.initials: AM
authors.lastname: Damas
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics*; D003001:Cloning, Molecular; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D020836:Protein Structure, Quaternary; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D008565:Membrane Proteins; C493653:TTL protein, Arabidopsis