Disease relevance of TOPP1

• The influence of the plant water-stress hormone abscisic acid (ABA) on anion channel activity and its interaction with protein kinase and phosphatase antagonists was examined in stomatal guard cells of wild-type Nicotiana benthamiana L. and of transgenic plants expressing the dominant-negative (mutant) Arabidopsis abi1-1 protein phosphatase [1].
• In each case, after over-expression in E. coli, the isolated proteins exhibited (Mg2+-dependent, okadeic acid-insensitive) protein phosphatase activity, although activity against 32P-phosphocasein varied among different PP2Cs [2].

High impact information on TOPP1

• We found that a type 5 protein phosphatase (PAPP5) specifically dephosphorylates biologically active Pfr-phytochromes and enhances phytochrome-mediated photoresponses [3].
• Arabidopsis ABA response gene ABI1: features of a calcium-modulated protein phosphatase [4].
• The phosphatase, designated KAPP (kinase-associated protein phosphatase), is composed of three domains: an amino-terminal signal anchor, a kinase interaction (KI) domain, and a type 2C protein phosphatase catalytic region [5].
• Two Arabidopsis loci that determine ABA sensitivity have already been cloned and found to encode a protein phosphatase and a transcriptional activator [6].
• Homeodomain protein ATHB6 is a target of the protein phosphatase ABI1 and regulates hormone responses in Arabidopsis [7].

Biological context of TOPP1

• The derived amino acid sequences of the TOPP clones are very similar to published sequences of PP1c from animals, fungi and plants [8].
• Previous studies in our laboratory indicated that maize and Arabidopsis contain a family of PP1 genes and/or pseudogenes [8].
• Six of the eight TOPP genes were mapped to different positions on four of five A. thaliana chromosomes [9].
• The PP1-At protein has strong similarity to all other known protein phosphatase type 1 catalytic subunits [10].
• Complementation of the cs dis2-11 cell cycle mutant of Schizosaccharomyces pombe by a protein phosphatase from Arabidopsis thaliana [10].

Anatomical context of TOPP1

• Using transient gene expression in rice protoplasts, we observed additive and inhibitory effects between maize VP1 (Viviparous-1, a transcriptional activator) and a dominant-negative mutant protein phosphatase, ABI1-1 (ABA-insensitive-1-1), from Arabidopsis [11].
• In particular, protein kinases and protein phosphatase were first identified as peroxisomal proteins suggesting that protein phosphorylation is one of the regulatory mechanisms in leaf peroxisomes [12].

Associations of TOPP1 with chemical compounds

• Pharmacological studies have led to a model in which the phytohormone abscisic acid (ABA) may be positively transduced via protein phosphatases of the type 1 (PP1) or type 2A (PP2A) families [13].
• Genetic and chemical reductions in protein phosphatase activity alter auxin transport, gravity response, and lateral root growth [14].
• Molecular characterization of a tyrosine-specific protein phosphatase encoded by a stress-responsive gene in Arabidopsis [15].
• From an Arabidopsis expression library, we isolated cDNA encoding a dual specificity protein phosphatase 1, which is capable of hydrolyzing both phosphoserine/threonine and phosphotyrosine residues of the substrates [16].
• ABI5-mediated transactivation was inhibited by overexpression of abi1-1, the dominant-negative allele of the protein phosphatase ABI1, and by 1-butanol, a competitive inhibitor of phospholipase D involved in ABA signaling [17].

Physical interactions of TOPP1

• These findings provide the first evidence for a plant protein phosphatase directly interacting with calmodulin and indicate that PP7 might be regulated by Ca(2+) levels in vivo [18].

Other interactions of TOPP1

• Deletion analysis led to the discovery of a novel protein domain of 37 amino acid residues, designated as the protein phosphatase interaction (PPI) motif, of SOS2 that is necessary and sufficient for interaction with ABI2 [19].
• Immunoprecipitation assays using antibodies generated to a peptide spanning amino acids 356 to 366 of TAP46 indicate that TAP46 is associated with a type 2A protein phosphatase in vivo [20].
• In summary, we have identified AtPTP1 as a tyrosine-specific protein phosphatase that may function in stress responses of higher plants [15].
• The 450-kD complex contains the protein phosphatase KAPP, which is a negative regulator of CLV1 signaling, and a Rho GTPase-related protein [21].
• In addition, we also detected transcripts for AtPP2CA, a protein phosphatase, that interacts with AKT2/3 [22].

Analytical, diagnostic and therapeutic context of TOPP1

• In cell cultures, the PP1 mRNA levels are differentially affected by treatment with drugs that block cell division [23].
• Identification and molecular cloning of two homologues of protein phosphatase X from Arabidopsis thaliana [24].
• The Arabidopsis thaliana type 1 protein phosphatase (PP1) catalytic subunit was released from its endogenous regulatory subunits by ethanol precipitation and purified by anion exchange and microcystin affinity chromatography [25].

References