High impact information on TWD1

• Employing an IAA-specific microelectrode demonstrated that IAA influx in the root elongation zone was perturbed and apically shifted in pgp1/pgp19 and twd1 roots [1].
• Constitutive overexpression of PGP1 and PGP19, but not TWD1, enhanced auxin export [1].
• Unlike AtPGP1, AtMRP1 binds to the C-terminal tetratricopeptide repeat domain of TWD1, which is well known to mediate protein-protein interactions [2].
• We demonstrate molecular interaction between TWD1 and ABC transporters AtMRP1 and its closest homologue, AtMRP2 [2].
• To further understand the dramatic pleiotropic phenotype that is caused by loss-of-function mutation of the TWD1 gene, we were interested in other TWD1 interacting proteins [2].

Biological context of TWD1

• Physiological and double mutant analyses suggest that UCU2 is required for growth and development and participates in auxin and brassinosteroid signaling [3].
• Here, we describe four recessive alleles of the UCU2 gene, whose homozygotes display helical rotation of several organs in addition to other phenotypic traits shared with ucu1 mutants [3].
• Following a map-based strategy, we identified the UCU2 gene, which was found to encode a peptidyl-prolyl cis/trans-isomerase of the FK506-binding protein family, whose homologs in metazoans are involved in cell signaling and protein trafficking [3].
• FKBP42 is a membrane-anchored immunophilin playing a critical role in morphogenesis and development of higher plants [4].
• Profound redox-dependence of PPIase activity implies oxidative activation of protein folding catalysis under oxidative stress and photosynthetic oxygen production in the thylakoid lumen of plant chloroplasts [5].

Anatomical context of TWD1

• We were able to demonstrate that TWD1 binds to isolated vacuoles and has a significant impact on the uptake of metolachlor-GS and estradiol-beta-glucuronide, well-known substrates of vacuolar transporters AtMRP1 and AtMRP2 [2].
• Unlike all other FKBPs, TWD1 is shown to be an integral membrane protein that colocalizes with its interacting partner AtPGP1 on the plasma membrane [6].
• While FKBP52 is found in the cytosol and translocates to the nucleus, AtFKBP42 was predicted to be membrane-localized, as shown by electron microscopy [7].
• These two enzymes are responsible for PPIase activity in both soluble and membrane-associated fractions of thylakoid lumen suggesting that other lumenal immunophilins are not active towards the peptide substrates [5].

Associations of TWD1 with chemical compounds

• The TWD1 gene encodes a 42 kDa FK506-binding protein (AtFKBP42) that possesses similarity to multidomain PPIases such as mammalian FKBP51 and FKBP52, which are known to be components of mammalian steroid hormone receptor complexes [7].

Physical interactions of TWD1

• Mapping of protein interaction domains shows that AtPGP1 surprisingly binds to the N-terminus of TWD1 harboring the cis-trans peptidyl-prolyl isomerase-like domain and not to the tetratrico-peptide repeat domain, which has been shown to mediate protein-protein interaction [6].

Other interactions of TWD1

• Coexpression of TWD1 and PGP1 in yeast and mammalian cells verified the specificity of the regulatory effect [1].
• By membrane fractionation and GFP-tagging, we localized AtMRP1 to the central vacuolar membrane and the TWD1-AtMRP1 complex was verified in vivo by coimmunoprecipitation [2].
• Null-mutations of the Arabidopsis FKBP-like immunophilin TWISTED DWARF1 (TWD1) gene cause a pleiotropic phenotype characterized by reduction of cell elongation and disorientated growth of all plant organs [6].

Analytical, diagnostic and therapeutic context of TWD1

• Crystallization and preliminary X-ray analysis of immunophilin-like FKBP42 from Arabidopsis thaliana [8].

References