Disease relevance of SPR

• Thus, autosomal recessive SR deficiency leads to BH(4) and to neurotransmitter deficiencies without hyperphenylalaninemia and may not be detected by neonatal screening for phenylketonuria [1].
• These data demonstrate that SPR mRNA expression is significantly reduced in patients with HIV infection [2].
• This confirms a previous study showing that SPR potentially modulates the onset of or risk for Parkinson's disease [3].
• SR mRNA expression is absent in the human NK-like cell line YT and in the murine erythroleukemia subclone B8/3, which both lack SR activity [4].
• To identify the G proteins involved in the function of human substance P receptor (hSPR), the receptor was expressed in Sf9 cells using the baculovirus expression system [5].

Psychiatry related information on SPR

• 2000 SPR Award for distinguished contributions to psychophysiology [6].
• Dopa-responsive hypersomnia and mixed movement disorder due to sepiapterin reductase deficiency [7].
• This reduced transcription rate for SPR promoter haplotypes 2 and 3 may impact on BH4-mediated neurotransmitter production, thus suggesting a biological process through which SPR gene variants might influence antidepressant response and susceptibility to bipolar disorder [8].

High impact information on SPR

• The other patient was a compound heterozygote for a genomic 5-bp deletion (1397-1401delAGAAC) resulting in abolished SPR-gene expression and an A-->G transition leading to an R150G amino acid substitution and to inactive SR as confirmed by recombinant expression [1].
• Mutations in the sepiapterin reductase gene cause a novel tetrahydrobiopterin-dependent monoamine-neurotransmitter deficiency without hyperphenylalaninemia [1].
• Investigation of skin fibroblasts revealed inactive sepiapterin reductase (SR), the enzyme catalyzing the final two-step reaction in the biosynthesis of BH(4) [1].
• SPR revealed calcium-independent interactions between VAMP(77-94) and liposomes containing phosphatidylserine, which blocked calmodulin binding [9].
• Further enzyme activities of tetrahydrobiopterin biosynthesis, i.e. 6-pyruvoyl tetrahydropterin synthase and sepiapterin reductase (EC 1.1.1.153), remained unchanged [10].

Chemical compound and disease context of SPR

• Ammonium sulfate precipitate fractions from lysates of E. coli expressing 14-3-3 protein and of cauliflower were investigated for specific binding to the phosphopeptide ligands immobilized on a sensorchip by SPR [11].
• Here we compare the impact of interferon-gamma treatment on activities of GTP-cyclohydrolase I (EC 3.5.4.16), 6-pyruvoyl tetrahydropterin synthase, and sepiapterin reductase (EC 1.1.1.153) in human peripheral blood-derived macrophages, normal dermal fibroblasts, THP-1 myelomonocytic cells, and the T 24 bladder transitional-cell carcinoma line [12].
• A novel type of NADPH-dependent sepiapterin reductase, which catalysed uniquely the reduction of sepiapterin to l-threo-dihydrobiopterin, was purified 533-fold from the cytosolic fraction of Chlorobium tepidum, with an overall yield of 3% [13].
• Activities for GTP-cyclohydrase-1, 6-pyruvoyltetrahydropterin synthase and sepiapterin reductase, enzymes essential for H(4)B biosynthesis, were present in Nocardia culture extracts at 77.5 pmol of neopterin and 45.8 pmol of biopterin h(-1) mg of protein(-1), respectively [14].
• The E. coli transformant produced sepiapterin, which was identified by high-performance liquid chromatography and enzymatically converted to dihydrobiopterin by sepiapterin reductase [15].

Biological context of SPR

• The nucleotide sequence of hSPR 8-25, which contained an entire coding region of the enzyme, was determined [16].
• The predicted amino acid sequence of human sepiapterin reductase showed a 74% identity with the rat enzyme [16].
• A full-length cDNA clone for sepiapterin reductase, an enzyme involved in tetrahydrobiopterin biosynthesis, was isolated from a human liver cDNA library by plaque hybridization [16].
• Lack of sepiapterin reductase activity, an autosomal recessive variant of BH(4) deficiency presenting without HPA, was diagnosed in patients with seven different mutant alleles in the SPR gene in exons 2 or 3 or in intron 2 [17].
• The human SPR gene was mapped to chromosome band 2p13 by fluorescence in situ hybridization [18].

Anatomical context of SPR

• Immunohistochemistry revealed SPR immunoreactivity in pyramidal neurons in the cerebral CTX, in a small number of striatal neurons, and in neurons of the hypothalamic and brain stem monoaminergic fields and olivary nucleus [19].
• Here, we characterize in detail GRK2-catalyzed phosphorylation of human SPR (hSPR) in intact membranes [20].
• In HEK-293 cells expressing either hSPRDelta325 or hSPR, SP-induced desensitization of the two receptors was similar when measured by inositol triphosphate accumulation or by transient translocation of coexpressed PKCbetaII-GFP to the plasma membrane [21].
• However, hSPR and hSPRDelta325 differ in their phosphorylation and in their ability to form beta-arrestin-containing endocytic vesicles [21].
• Therefore, in the present study we examined whether human SPR (hSPR) stably expressed in CHO cells activates multiple G proteins [22].

Associations of SPR with chemical compounds

• Double-staining immunohistochemistry showed that TH and SPR were colocalized in the SN dopamine neurons [19].
• Mutations in the BH4-metabolizing genes GTP cyclohydrolase I, 6-pyruvoyl-tetrahydropterin synthase, sepiapterin reductase, carbinolamine-4a-dehydratase, and dihydropteridine reductase [17].
• In addition, the antiestrogen tamoxifen (1 microM) blocked the stimulatory effect of E2 on SPR mRNA [23].
• Using Northern blot analysis of SPR mRNA levels, we studied the effects of 17beta-estradiol (E2) on SPR gene expression in AR42J (rat pancreatic acinar) cells which constitutively express high levels of SPR [23].
• Involvement of G beta gamma endogenously present in membranes is ruled out as a source of high levels of hSPR phosphorylation, since receptor phosphorylation was not affected by guanine nucleotides that suppress or enhance the release of endogenous G beta gamma [20].

Enzymatic interactions of SPR

• The sepiapterin reductase catalyzed the transfer of the pro-S hydrogen of NADPH during the reduction of sepiapterin to BH2 [24].

Other interactions of SPR

• Whereas TH protein showed a restricted localization, being mainly detected in the SN and CN, SPR protein was detected in all brain regions examined [19].
• The results indicate that there might be a BH4 biosynthetic pathway where GCH is not involved and that SPR might have some yet unidentified function(s) in addition to BH4 biosynthesis [19].
• The sepiapterin reductase gene region reveals association in the PARK3 locus: analysis of familial and sporadic Parkinson's disease in European populations [3].
• In order to investigate their putative function and biosynthetic regulation, we performed quantitative analysis of not only the intracellular pteridines by HPLC but also the biosynthetic enzymes (GTP cyclohydrolase I, 6-pyruvoyltetrahydropterin synthase, SR, and aldose reductase-like enzyme) by Northern blot analysis and activity assay [25].
• We found that both SR transcript and activity increased in parallel with a remarkable decline in aldose reductase-like enzyme activity when BH4 increased transiently in the early development [25].

Analytical, diagnostic and therapeutic context of SPR

• The purpose of this study was to characterize intestinal mucosal SPR mRNA expression in control, HIV and IBD patients using semiquantitative reverse transcription PCR [2].
• In contrast, uniform increases in mucosal SP receptor (SPR) have been described in patients with IBD using quantitative autoradiography [2].
• This was achieved by photoaffinity labeling of G(alpha)-subunits with [32P]azidoanilido-GTP ([32P]AA-GTP) upon hSPR stimulation in CHO-hSPR membranes followed by immunoprecipitation of the labeled G(alpha)-subunits with antibodies specific for various G(alpha)-subunits [22].
• The physical properties of the mutants were carefully examined by gel-filtration chromatography, CD, and NMR spectroscopy, and the biological activities were assessed by an in vitro SPR bioassay and three in vivo bioassays: binding to cells, blocking virus infection and blocking cell fusion [26].
• SPR biosensor studies of the direct interaction between 27 drugs and a liposome surface: correlation with fraction absorbed in humans [27].

References