Analysis of the ACP1 gene product: classification as an FMN phosphatase

An FMN hydrolase of the haloacid dehalogenase superfamily is active in plant chloroplasts

FMN hydrolases catalyze dephosphorylation of FMN to riboflavin. Although these enzymes have been described in many organisms, few had their corresponding genes cloned and their recombinant proteins biochemically characterized, and none had their physiological roles determined. We found previously that FMN hydrolase activity in pea chloroplasts is Mg(2+)-dependent, suggesting an enzyme of the haloacid dehalogenase (HAD) superfamily. In this study, a new FMN hydrolase was purified by multistep chromatography after ammonium sulfate precipitation. The molecular weight of the native protein was estimated at ∼59,400, a dimer of about twice the predicted molecular weight of most HAD superfamily phosphatases. After SDS-PAGE of the partially purified material, two separate protein bands within 25-30 kDa were extracted from the gel and analyzed by nanoLC-MS/MS. Peptide sequence matching to the protein samples suggested the presence of three HAD-like hydrolases. cDNAs for sequence homologs from Arabidopsis thaliana of these proteins were expressed in Escherichia coli. Activity screening of the encoded proteins showed that the At1g79790 gene encodes an FMN hydrolase (AtcpFHy1). Plastid localization of AtcpFHy1 was confirmed using fluorescence microscopy of A. thaliana protoplasts transiently expressing the N-terminal fusion of AtcpFHy1 to enhanced green fluorescent protein. Phosphatase activity of AtcpFHy1 is FMN-specific, as assayed with 19 potential substrates. Kinetic parameters and pH and temperature optima for AtcpFHy1 were determined. A phylogenetic analysis of putative phosphatases of the HAD superfamily suggested distinct evolutionary origins for the plastid AtcpFHy1 and the cytosolic FMN hydrolase characterized previously.

Body mass index and acid phosphatase locus 1 in diabetic disorders

The polymorphic enzyme acid phosphatase locus 1 (ACP1) is a candidate gene for obesity disorders. The enzyme is able to dephosphorylate the insulin receptor. Our group has observed a lower plasma glucose level in diabetic subjects carrying the low activity ACP1 phenotypes A and BA, and a positive association between these genotypes and body mass index (BMI). We have now analysed the relationship between BMI and ACP1 in gestational diabetes and in women with type 1 diabetes. We have studied 106 Caucasian women with type 1 diabetes who had previously delivered a liveborn infant, 99 Caucasian women who had had gestational diabetes and 387 healthy fertile women from the same population as controls. ACP1 phenotype was determined by starch gel electrophoresis. In overweight women (BMI > 25), the proportion of low activity ACP1 phenotypes is much lower in type 1 diabetes than in gestational diabetes and in healthy females. In women with BMI ≤ 25, the proportion of low activity ACP1 phenotypes is slightly lower in gestational diabetes than in type 1 diabetes. Low activity ACP1 phenotypes have diverse effects on susceptibility to overweight depending on the class of diabetic disorder: in subjects with type 2 diabetes and in subjects with gestational diabetes low activity ACP1 phenotypes predispose to an increase in BMI, while in type 1 diabetes these ACP1 phenotypes seem to protect from overweight.

Flavin nucleotide metabolism in plants: monofunctional enzymes synthesize fad in plastids

FAD synthetases (EC 2.7.7.2) catalyze biosynthesis of FAD from FMN and ATP. Monofunctional FAD synthetases are known to exist in mammals and yeast; bifunctional enzymes also catalyzing phosphorylation of riboflavin to FMN are known to exist in bacteria. Previously known eukaryotic enzymes with FAD synthetase activity have no sequence similarity to prokaryotic enzymes with riboflavin kinase and FAD synthetase activities. Proteins homologous to bacterial bifunctional FAD synthetases, yet shorter and lacking amino acid motifs at the C terminus, were found by bioinformatic analyses in vascular plant genomes, suggesting that plants contain a type of FAD synthetase previously known to exist only in prokaryotes. The Arabidopsis thaliana genome encodes two of such proteins. Both proteins, which we named AtRibF1 and AtRibF2, carry N-terminal extensions with characteristics of organellar targeting peptides. AtRibF1 and AtRibF2 cDNAs were cloned by reverse transcription-PCR. Only FAD synthetase activity was detected in the recombinant enzymes produced in Escherichia coli. FMN and ATP inhibited both enzymes. Kinetic parameters of AtRibF1 and AtRibF2 for the two substrates were similar. Confocal microscopy of protoplasts transformed with enhanced green fluorescence protein-fused proteins showed that AtRibF1 and AtRibF2 are targeted to plastids. In agreement with subcellular localization to plastids, Percoll-isolated chloroplasts from pea (Pisum sativum) synthesized FAD from imported riboflavin. Riboflavin kinase, FMN hydrolase, and FAD pyrophosphatase activities were detected in Percoll-isolated chloroplasts and mitochondria from pea. We propose from these new findings a model for subcellular distribution of enzymes that synthesize and hydrolyze flavin nucleotides in plants.

The genetics of feto-placental development: a study of acid phosphatase locus 1 and adenosine deaminase polymorphisms in a consecutive series of newborn infants

BACKGROUND

Acid phosphatase locus 1 and adenosine deaminase locus 1 polymorphisms show cooperative effects on glucose metabolism and immunological functions. The recent observation of cooperation between the two systems on susceptibility to repeated spontaneous miscarriage prompted us to search for possible interactional effects between these genes and the correlation between birth weight and placental weight. Deviation from a balanced development of the feto-placental unit has been found to be associated with perinatal morbidity and mortality and with cardiovascular diseases in adulthood.

METHODS

We examined 400 consecutive newborns from the Caucasian population of Rome. Birth weight, placental weight, and gestational length were registered. Acid phosphatase locus 1 and adenosine deaminase locus 1 phenotypes were determined by starch gel electrophoresis and correlation analysis was performed by SPSS programs. Informed verbal consent to participate in the study was obtained from the mothers.

RESULTS

Highly significant differences in birth weight-placental weight correlations were observed among acid phosphatase locus 1 phenotypes (p = 0.005). The correlation between birth weight and placental weight was markedly elevated in subjects carrying acid phosphatase locus 1 phenotypes with medium-low F isoform concentration (A, CA and CB phenotypes) compared to those carrying acid phosphatase locus 1 phenotypes with medium-high F isoform concentration (BA and B phenotypes) (p = 0.002). Environmental and developmental variables were found to exert a significant effect on birth weight-placental weight correlation in subjects with medium-high F isoform concentrations, but only a marginal effect was observed in those with medium-low F isoform concentrations. The correlation between birth weight and placental weight is higher among carriers of the adenosine deaminase locus 1 allele*2, which is associated with low activity, than in homozygous adenosine deaminase locus 1 phenotype 1 carriers (p = 0.04). The two systems show a cooperative effect on the correlation between birth weight and placental weight: the highest value is observed in newborns carrying adenosine deaminase locus 1 allele*2 and acid phosphatase locus 1 phenotypes with medium-low F isoform concentration (p = 0.005).

CONCLUSION

These data suggest that zygotes with low adenosine deaminase locus 1 activity and low F activity may experience the most favourable intrauterine conditions for a balanced development of the feto-placental unit.

Repeated spontaneous abortion. Cooperative effects of ADA and ACP1 genetic polymorphisms

PROBLEM

In consideration of the effect of adenosine deaminase (ADA) and ACP1 (a low-molecular-weight protein tyrosine phosphatase) on T-cell receptor activity, we have analysed the joint distribution of these polymorphisms in a sample of women with primary repeated spontaneous abortion (RSA) to search for possible interactive effects on susceptibility to RSA.

METHOD OF STUDY

ACP1 and ADA phenotypes were determined in 170 women with primary RSA in 79 healthy consecutive puerperae and in 160 female newborns from the Caucasian population of Rome and in 357 healthy consecutive puerperae from the Caucasian population of Penne. Chi-square test of independence and three way contingency table analysis by a log-linear model were performed.

RESULTS

Women with low-ADA activity and high-ACP1 activity show the lowest susceptibility to RSA. Women with high-ADA activity and low-ACP1 activity, on the contrary, show the highest susceptibility to RSA and also the highest incidence of auto antibodies and of A blood group incompatibility.

CONCLUSION

The data are in agreement with those expected on the basis of the effects of ACP1 and ADA genetic variability on T-cell receptor activity and suggest a cooperative effect of the two polymorphic systems in the susceptibility/resistance to repeated spontaneous abortion.

ACP1 and Th Class of Immunological Disease: Evidence of Interaction with Gender

BACKGROUND

Data collected by our group in the past years indicate a relationship between ACP1 genetic polymorphism and susceptibility/resistance to immunological diseases. Recent observations suggest that through modulation of ZAP-70 activity, the enzyme may influence T cell activation. In view of the current interest in gender differences in autoimmune diseases we reviewed our data to enlighten possible effects of gender on the relationship between ACP1 and class of immunological disease.

METHODS

We studied three samples of subjects with allergic disorders of a total of 299 subjects, 71 subjects with Crohn's disease and 188 children with type 1 diabetes. Three-way contingency tables were analyzed by a log linear model and two-way contingency tables by chi(2) test.

RESULTS

There is an association between ACP1 and allergy (Th2 class) that depends on gender: the presence of the ACP1*A allele seems to make females more susceptible to allergic manifestations as compared to males. ACP1 is also associated with Crohn's disease and type 1 diabetes: the relationship between this class (Th1) of immunological diseases and ACP1 depends on gender. The presence of *A allele seems to make females less susceptible to this class of diseases as compared to males.

CONCLUSIONS

The ACP1*A allele which is associated with low ACP1 activity appears responsible for a complex relationship involving gender, ACP1 and Th1/Th2 orientation. Low ACP1 activity influencing ZAP-70 activity and in turn T cell activation seems to have opposite effects on Th1/Th2 orientation depending on gender.

Feto-maternal ACP1 activity ratio and intrauterine survival

OBJECTIVE

Genetic differences in the activity of phosphotyrosine phosphatases between mother and embryo could result in a differential activation of signals induced by growth factors in the two sides of placenta. Previous observations suggest that this may have important effects on intrauterine development and survival. The aim of the present study is to confirm previous observations and show new data.

STUDY DESIGN

We have studied 573 mother/newborn pairs, 169 wife/husband couples with repeated spontaneous abortion and 34 fertile wife/husband couples

RESULTS

In mother/newborn pairs, the analysis of joint mother/infant ACP1 distribution has shown a deficit of pairs with the mother having low ACP1 S isoform concentration and the infant having high S isoform concentration, and an excess of pairs with the mother having high S isoform concentration and the infant having low S isoform concentration. In RSA couples there is an excess of couples in which the wife has low S isoform concentration and the husband has high S isoform concentration and a deficit of couples in which the wife has high S isoform concentration and the husband has low S isoform concentration. In fertile couples the pattern is reversed.

CONCLUSION

The data suggest that when the mother to fetus S isoform concentration ratio is in favour of the mother, the probability of survival of the fetus is greater than in the opposite situation.

An FMN hydrolase is fused to a riboflavin kinase homolog in plants

Riboflavin kinases catalyze synthesis of FMN from riboflavin and ATP. These enzymes have to date been cloned from bacteria, yeast, and mammals, but not from plants. Bioinformatic approaches suggested that diverse plant species, including many angiosperms, two gymnosperms, a moss (Physcomitrella patens), and a unicellular green alga (Chlamydomonas reinhardtii), encode proteins that are homologous to riboflavin kinases of yeast and mammals, but contain an N-terminal domain that belongs to the haloacid dehalogenase superfamily of enzymes. The Arabidopsis homolog of these proteins was cloned by RT-PCR, and was shown to have riboflavin kinase and FMN hydrolase activities by characterizing the recombinant enzyme produced in Escherichia coli. Both activities of the purified recombinant Arabidopsis enzyme (AtFMN/FHy) increased when the enzyme assays contained 0.02% Tween 20. The FMN hydrolase activity of AtFMN/FHy greatly decreased when EDTA replaced Mg(2+) in the assays, as expected for a member of the Mg(2+)-dependent haloacid dehalogenase family. The functional overexpression of the individual domains in E. coli establishes that the riboflavin kinase and FMN hydrolase activities reside, respectively, in the C-terminal (AtFMN) and N-terminal (AtFHy) domains of AtFMN/FHy. Biochemical characterization of AtFMN/FHy, AtFMN, and AtFHy shows that the riboflavin kinase and FMN hydrolase domains of AtFMN/FHy can be physically separated, with little change in their kinetic properties.

Type 2 diabetes and the genetics of signal transduction: a study of interaction between adenosine deaminase and acid phosphatase locus 1 polymorphisms

Acid phosphatase locus 1 (ACP1) is a highly polymorphic enzyme that has an important role in flavoenzyme activity and in the control of insulin receptor activity and band 3 protein phosphorylation status. Adenosine deaminase (ADA) is a polymorphic enzyme that catalyses the irreversible deamination of adenosine to inosine and has an important role in regulating adenosine concentration. Based on the hypothesis that ACP1 counteracts insulin signaling by dephosphorylating the insulin receptor and that adenosine has an anti-insulin action, we reasoned that low ACP1 activity (low dephosphorylating action on insulin receptor) when associated with high ADA activity (low adenosine concentration) would result in a cumulative effect towards an increased glucose tolerance. On the contrary, high ACP1 activity when associated with low ADA activity would result in a cumulative effect towards a decreased glucose tolerance. A total of 280 adult subjects with type 2 diabetes from the population of Penne (Italy) were studied. There was a nonsignificant trend toward an increase in the proportion of subjects with the complex type with high ACP1 activity and low ADA activity (ie, *B/*B; *A/*C; *B/*C; *C/*C//ADA*1/*2 and *2/*2) in type 2 diabetes relative to that observed in newborn infants from the same population. High ACP1 activity/low ADA activity joint genotype was positively associated with high glycemic levels and with high body mass index (BMI) values. Low ACP1 activity/high ADA activity joint genotype was also positively associated with dyslipidemia. These findings suggest that both ACP1 and ADA contribute to the clinical manifestations of type 2 diabetes and probably also have a marginal influence on susceptibility to the disease. Both additive and epistatic interactions between the 2 systems seem to be operative.

ACP1 and human adaptability: association with past malarial morbidity in the Sardinian population

Acid Phosphatase locus 1 (ACP1) is a polymorphic enzyme controlled by a locus on chromosome 2 with three common codominant alleles: *A, *B, and *C. ACP1 shows two major isoforms, F and S. The ratio of their concentration differs markedly among genotypes. Two functions have been proposed for the enzyme: flavin-mononucleotide phosphatase and tyrosine phosphatase activity. An association between ACP1 polymorphism and past malarial morbidity in Sardinia and the Po Valley has been described. Genetic polymorphisms could contribute to natural resistance or susceptibility to the disease. On the other hand, malaria pressure may select for genes that increase susceptibility to common diseases of modern civilization. Thus, the association between ACP1 and malaria in Sardinia in the light of recent understanding of the function of ACP1 and the molecular basis of malaria pathophysiology, especially aspects of the structure of band 3 protein (B3P) and the role of cytokines have been revisited. There is a significant negative correlation between ACP1 S isoform concentration, directly related to the ACP1*C allele, and past malarial morbidity in Sardinia. Populations subjected in the past to a heavy malarial burden show, at present, a lower concentration of the S isoform compared to a nearby malaria-free population, suggesting that genotypes with high S isoform concentration have been subjected to negative selection in a malarial environment. Correlation analysis and analysis of the joint G-6-PD/ACP1 distribution suggest that the relationship between past endemic malaria and the S isoform has not been mediated by glucose-6-phosphate dehydrogenase (G-6-PD) deficiency, thus pointing to a direct effect of malaria on ACP1.

Acid phosphatase locus 1 (ACP1): Possible relationship of allelic variation to body size and human population adaptation to thermal stress-A theoretical perspective

The acid phosphatase locus 1 (ACP1) codes for a low molecular weight phosphotyrosine protein phosphatase that has the important action of dephosphorylating tyrosine phosphorylated proteins and peptides and a second important role in modulating flavin cofactor levels and the activity of flavo-enzymes. These functions significantly influence cell division, differentiation, and growth. Two alleles (ACP1*A and ACP1*B) reach polymorphic frequencies at the ACP1 locus in all human populations, while the ACP1*C and ACP1*R alleles reach polymorphic frequencies in restricted geographical regions. The worldwide distribution of these alleles, and data from several clinical studies, strongly suggest that the ACP1 locus functions to modulate growth and that selection at this locus is a component of the selective processes influencing body mass and human population adaptation to thermal stress. The ACP1*A allele reaches highest frequencies at extreme latitudes and appears to be associated with maximizing body mass and adaptation to cold stress, whereas the ACP1*B allele reaches highest frequencies in tropical and subtropical environments and appears to be associated with minimizing body mass and adaptation to heat stress. The high frequency of the ACP1*C allele at northern latitudes, where ACP1*A allele frequencies are elevated, may be a mechanism for limiting fetal and maternal complications associated with fetal macrosomia and adult obesity in populations where protein and calorie intake are relatively high. Am. J. Hum. Biol. 12:688-701, 2000. Copyright 2000 Wiley-Liss, Inc.

Adenosine deaminase-acid phosphatase association and the environment: A study in a continental Italian population

Three hundred fifty newborns from Rome and 351 from Penne were studied in continental Italy. Medium high altitude above sea level and cold winters characterize the area of Penne, while low altitude and very mild winters characterize the area of Rome. An effect of environmental conditions on the association between adenosine deaminase (ADA) and acid phosphatase (ACP1), previously shown in Sardinia, has been confirmed in continental Italy. When compared with expected independent assortment, the proportion of ACP1*A/*A carrying the ADA*2 allele is lower than expected in the lowlands and higher than expected in highlands. In continental Italy there is an interaction among ACP1-ADA genotype, season of conception, and locality. The excess of *A/*A newborns carrying the ADA*2 allele is present only among those conceived in the first half of the year (January-June). Among newborns in Penne conceived in the Spring, the proportion of those with *A/*A genotype is increased and these infants show decreased intrauterine growth. The present data suggest that ADA and ACP1 interact during intrauterine life with effects on development and survival and that such effects are dependent on local environment and season of conception. Am. J. Hum. Biol. 12:214-220, 2000. Copyright 2000 Wiley-Liss, Inc.

Kinetic characterization of bovine lung low-molecular-weight protein tyrosine phosphatase

Protein tyrosine phosphatase is an important class of enzymes that plays an essential role in the cellular proliferation, differentiation, and oncogenesis. In this paper we report characterization of a low-molecular-weight protein tyrosine phosphatase purified from bovine lung. The enzyme activity was essentially independent of metal ions and sensitive to sulfhydryl reagents. Both vanadate and inorganic phosphate are competitive inhibitors, with Ki values of 0.38 microM and 0.28 mM, respectively. Besides p-nitrophenyl phosphate, the enzyme was also able to efficiently hydrolyze tyrosine phosphate, beta-naphthyl phosphate, and flavine mononucleotide.

Enzymic formation of riboflavin 4',5'-cyclic phosphate from FAD: evidence for a specific low-Km FMN cyclase in rat liver1

An enzyme activity splitting FAD to AMP and riboflavin 4',5'-cyclic phosphate (4',5'-cFMN), with a Km of 6-8 microM, was partially purified from the cytosolic fraction of rat liver homogenates. 4', 5'-cFMN was characterized by enzyme, HPLC, UV-visible and NMR spectroscopic analyses. The data suggest that a novel enzyme, tentatively named FAD-AMP lyase (cyclizing) or FMN cyclase, is involved. Also, 4',5'-cFMN was hydrolysed to 5'-FMN by a rat liver cyclic phosphodiesterase. The results indicate a novel enzymic pathway for flavins in mammals, and support the biological relevance of 4',5'-cFMN, perhaps as a flavocoenzyme or a regulatory signal.

Phosphotyrosine protein phosphatases and diabetic pregnancy: an association between low molecular weight acid phosphatase and degree of glycemic control

Low molecular weight acid phosphatase encoded by the highly polymorphic locus ACP1 is a member of the protein-tyrosin phosphatase family (PTPases) which plays an essential role in the control of receptor signalling through phosphotyrosine pathways. Recent experiments have shown that purified rat liver ACP, corresponding to human ACP1, is able to hydrolyze a phosphotyrosine-containing synthetic peptide corresponding to the 1146-1158 sequence of the human insulin receptor, and shows a high affinity for it. This prompted us to analyze the degree of glycemic control in relation to ACP1 genetic variability in a sample of 214 diabetic pregnant women including IDDM, NIDDM and gestational diabetes. The ACP1 genotype was also determined in 482 non-diabetic pregnant women. In diabetic women glycemic levels in the last trimester of pregnancy appear to be significantly associated with the ACP1 genotype, and correlate positively with ACP1 enzymatic activity. The data suggest that quantitative variations of ACP1 may influence the clinical manifestations of diabetic disorders, and call for further studies on the role of this enzyme in the modulation of insulin-receptor phosphotyrosine pathways.

ACP1 and human adaptability. 1. Association with common diseases: a case-control study

Human red cell acid phosphatase (ACP1) is a polymorphic enzyme closely related to cytosolic low molecular weight acid phosphatases, a protein family broadly conserved among eukaryotes. Two different functions have been proposed for ACP1: flavin mononucleotide (FMN) phosphatase and phosphotyrosine phosphatase (PTPase). Given that genetic variants of ACP1 activity are common, the enzyme could have a role in regulating a large spectrum of cellular functions and, in turn, disease susceptibility. In the present paper we report a study of ACP1 genetic polymorphism in 1088 normal subjects and in 1267 subjects from the population of Rome admitted to hospital for a number of common diseases. All ACP1 parameters investigated show highly significant differences among samples, suggesting that the enzyme may have a significant role in some of the diseases considered. In particular, consistent associations of ACP1 with developmental disturbances and with hemolytic favism have been observed. In the majority of diseases showing association with ACP1, only one of the two ACP1 isoforms, f and s, is involved, supporting the hypothesis of a functional differentiation between the two enzymatic fractions.

Haptoglobin development in newborn infants from diabetic mothers

Haptoglobin (Hp) development during the neonatal period has been studied in 325 newborn infants from normal pregnancies and in 242 infants from diabetic mothers. In infants from diabetic mothers Hp development is delayed as compared to infants from normal pregnancies. This delay is associated with a change in the pattern of relationship between Hp development and the polymorphism of acid phosphatase (ACP1) (an enzyme which shows phosphotyrosine phosphatase (PTPase) activity). In infants from normal pregnancies who show ACP1 phenotypes with the highest activity, the appearance of Hp is accelerated as compared to other infants. In contrast, infants from diabetic pregnancies who have ACP1 phenotypes with the highest activity, show delayed Hp development.

Genetic and non genetic factors in the outcome of diabetic pregnancy

In insulin-dependent diabetes mellitus, maternal Phosphoglucomutase genotype is a predictor of fetal macrosomia much more important than quality of metabolic control during pregnancy. In gestational diabetes and in non insulin-dependent diabetes, on the contrary, the most important predictor is the metabolic control of diabetes.