44 research outputs found
The structure of a class 3 nonsymbiotic plant haemoglobin from<i>Arabidopsis thaliana</i>reveals a novel N-terminal helical extension
Plant nonsymbiotic haemoglobins fall into three classes, each with distinct properties but all with largely unresolved physiological functions. Here, the first crystal structure of a class 3 nonsymbiotic plant haemoglobin, that fromArabidopsis thaliana, is reported to 1.77 Å resolution. The protein forms a homodimer, with each monomer containing a two-over-two α-helical domain similar to that observed in bacterial truncated haemoglobins. A novel N-terminal extension comprising two α-helices plays a major role in the dimer interface, which occupies the periphery of the dimer–dimer face, surrounding an open central cavity. The haem pocket contains a proximal histidine ligand and an open sixth iron-coordination site with potential for a ligand, in this structure hydroxide, to form hydrogen bonds to a tyrosine or a tryptophan residue. The haem pocket appears to be unusually open to the external environment, with another cavity spanning the entrance of the two haem pockets. The final 23 residues of the C-terminal domain are disordered in the structure; however, these domains in the functional dimer are adjacent and include the only two cysteine residues in the protein sequence. It is likely that these residues form disulfide bondsin vitroand it is conceivable that this C-terminal region may act in a putative complex with a partner moleculein vivo.</jats:p
Non-symbiotic haemoglobins—What's happening beyond nitric oxide scavenging?
The ating evidence suggests non-symbiotic hemoglobins affect hormone responses by scavenging NO. Auxin, jasmonic acid, salicylic acid, ethylene and abscisic acid have altered responses when hemoglobins are expressed. Non-symbiotic hemoglobin is a factor during plant development, biotic and abiotic stress
Insights into the TOR-S6K Signaling Pathway in Maize (<i>Zea mays</i> L.). Pathway Activation by Effector–Receptor Interaction
The
primordial TOR pathway, known to control growth and cell proliferation,
has still not been fully described for plants. Nevertheless, in maize,
an insulin-like growth factor (ZmIGF) peptide has been reported to
stimulate this pathway. This research provides further insight into
the TOR pathway in maize, using a biochemical approach in cultures
of fast-growing (FG) and slow-growing (SG) calli, as a model system.
Our results revealed that addition of either ZmIGF or insulin to SG
calli stimulated DNA synthesis and increased the growth rate through
cell proliferation and increased the rate of ribosomal protein (RP)
synthesis by the selective mobilization of RP mRNAs into polysomes.
Furthermore, analysis of the phosphorylation status of the main TOR
and S6K kinases from the TOR pathway revealed stimulation by ZmIGF
or insulin, whereas rapamycin inhibited its activation. Remarkably,
a putative maize insulin-like receptor was recognized by a human insulin
receptor antibody, as demonstrated by immunoprecipitation from membrane
protein extracts of maize callus. Furthermore, competition experiments
between ZmIGF and insulin for the receptor site on maize protoplasts
suggested structural recognition of the putative receptor by either
effector. These data were confirmed by confocal immunolocalization
within the cell membrane of callus cells. Taken together, these data
indicate that cell growth and cell proliferation in maize depend on
the activation of the TOR-S6K pathway through the interaction of an
insulin-like growth factor and its receptor. This evidence suggests
that higher plants as well as metazoans have conserved this biochemical
pathway to regulate their growth, supporting the conclusion that it
is a highly evolved conserved pathway