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VanOrsdel CE, Kelly JP, Burke BN, Lein CD, Oufiero CE, Sanchez JF, Wimmers LE, Hearn DJ, Abuikhdair FJ, Barnhart KR, Duley ML, Ernst SEG, Kenerson BA, Serafin AJ, Hemm MR. Identifying New Small Proteins in Escherichia coli. Proteomics 2018; 18:e1700064. [PMID: 29645342 PMCID: PMC6001520 DOI: 10.1002/pmic.201700064] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2017] [Revised: 03/05/2018] [Indexed: 12/11/2022]
Abstract
The number of small proteins (SPs) encoded in the Escherichia coli genome is unknown, as current bioinformatics and biochemical techniques make short gene and small protein identification challenging. One method of small protein identification involves adding an epitope tag to the 3′ end of a short open reading frame (sORF) on the chromosome, with synthesis confirmed by immunoblot assays. In this study, this strategy was used to identify new E. coli small proteins, tagging 80 sORFs in the E. coli genome, and assayed for protein synthesis. The selected sORFs represent diverse sequence characteristics, including degrees of sORF conservation, predicted transmembrane domains, sORF direction with respect to flanking genes, ribosome binding site (RBS) prediction, and ribosome profiling results. Of 80 sORFs, 36 resulted in encoded synthesized proteins—a 45% success rate. Modeling of detected versus non‐detected small proteins analysis showed predictions based on RBS prediction, transcription data, and ribosome profiling had statistically‐significant correlation with protein synthesis; however, there was no correlation between current sORF annotation and protein synthesis. These results suggest substantial numbers of small proteins remain undiscovered in E. coli, and existing bioinformatics techniques must continue to improve to facilitate identification.
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Affiliation(s)
- Caitlin E VanOrsdel
- Department of Biological Sciences, Smith Hall, Towson University, Towson, MD, USA
| | - John P Kelly
- Department of Biological Sciences, Smith Hall, Towson University, Towson, MD, USA
| | - Brittany N Burke
- Department of Biological Sciences, Smith Hall, Towson University, Towson, MD, USA
| | - Christina D Lein
- Department of Biological Sciences, Smith Hall, Towson University, Towson, MD, USA
| | | | - Joseph F Sanchez
- Department of Biological Sciences, Smith Hall, Towson University, Towson, MD, USA
| | - Larry E Wimmers
- Department of Biological Sciences, Smith Hall, Towson University, Towson, MD, USA
| | - David J Hearn
- Department of Biological Sciences, Smith Hall, Towson University, Towson, MD, USA
| | - Fatimeh J Abuikhdair
- Department of Biological Sciences, Smith Hall, Towson University, Towson, MD, USA
| | - Kathryn R Barnhart
- Department of Biological Sciences, Smith Hall, Towson University, Towson, MD, USA
| | - Michelle L Duley
- Department of Biological Sciences, Smith Hall, Towson University, Towson, MD, USA
| | - Sarah E G Ernst
- Department of Biological Sciences, Smith Hall, Towson University, Towson, MD, USA
| | - Briana A Kenerson
- Department of Biological Sciences, Smith Hall, Towson University, Towson, MD, USA
| | - Aubrey J Serafin
- Department of Biological Sciences, Smith Hall, Towson University, Towson, MD, USA
| | - Matthew R Hemm
- Department of Biological Sciences, Smith Hall, Towson University, Towson, MD, USA
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Allen RJ, Brenner EP, VanOrsdel CE, Hobson JJ, Hearn DJ, Hemm MR. Conservation analysis of the CydX protein yields insights into small protein identification and evolution. BMC Genomics 2014; 15:946. [PMID: 25475368 PMCID: PMC4325964 DOI: 10.1186/1471-2164-15-946] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2014] [Accepted: 11/10/2014] [Indexed: 11/27/2022] Open
Abstract
Background The reliable identification of proteins containing 50 or fewer amino acids is difficult due to the limited information content in short sequences. The 37 amino acid CydX protein in Escherichia coli is a member of the cytochrome bd oxidase complex, an enzyme found throughout Eubacteria. To investigate the extent of CydX conservation and prevalence and evaluate different methods of small protein homologue identification, we surveyed 1095 Eubacteria species for the presence of the small protein. Results Over 300 homologues were identified, including 80 unannotated genes. The ability of both closely-related and divergent homologues to complement the E. coli ΔcydX mutant supports our identification techniques, and suggests that CydX homologues retain similar function among divergent species. However, sequence analysis of these proteins shows a great degree of variability, with only a few highly-conserved residues. An analysis of the co-variation between CydX homologues and their corresponding cydA and cydB genes shows a close synteny of the small protein with the CydA long Q-loop. Phylogenetic analysis suggests that the cydABX operon has undergone horizontal gene transfer, although the cydX gene likely evolved in a progenitor of the Alpha, Beta, and Gammaproteobacteria. Further investigation of cydAB operons identified two additional conserved hypothetical small proteins: CydY encoded in CydAQlong operons that lack cydX, and CydZ encoded in more than 150 CydAQshort operons. Conclusions This study provides a systematic analysis of bioinformatics techniques required for the unique challenges present in small protein identification and phylogenetic analyses. These results elucidate the prevalence of CydX throughout the Proteobacteria, provide insight into the selection pressure and sequence requirements for CydX function, and suggest a potential functional interaction between the small protein and the CydA Q-loop, an enigmatic domain of the cytochrome bd oxidase complex. Finally, these results identify other conserved small proteins encoded in cytochrome bd oxidase operons, suggesting that small protein subunits may be a more common component of these enzymes than previously thought. Electronic supplementary material The online version of this article (doi:10.1186/1471-2164-15-946) contains supplementary material, which is available to authorized users.
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Affiliation(s)
| | | | | | | | | | - Matthew R Hemm
- Department of Biological Sciences, Towson University, Towson 21252MD, USA.
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Opdyke JA, Fozo EM, Hemm MR, Storz G. RNase III participates in GadY-dependent cleavage of the gadX-gadW mRNA. J Mol Biol 2010; 406:29-43. [PMID: 21147125 DOI: 10.1016/j.jmb.2010.12.009] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2010] [Revised: 12/02/2010] [Accepted: 12/03/2010] [Indexed: 10/18/2022]
Abstract
The adjacent gadX and gadW genes encode transcription regulators that are part of a complex regulatory circuit controlling the Escherichia coli response to acid stress. We previously showed that the small RNA GadY positively regulates gadX mRNA levels. The gadY gene is located directly downstream of the gadX coding sequence on the opposite strand of the chromosome. We now report that gadX is transcribed in an operon with gadW, although this full-length mRNA does not accumulate. Base pairing of the GadY small RNA with the intergenic region of the gadX-gadW mRNA results in directed processing events within the region of complementarity. The resulting two halves of the cleaved mRNA accumulate to much higher levels than the unprocessed mRNA. We examined the ribonucleases required for this processing, and found that multiple enzymes are involved in the GadY-directed cleavage including the double-strand RNA-specific endoribonuclease RNase III.
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Affiliation(s)
- Jason A Opdyke
- Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and HumanDevelopment, Bethesda, MD 20892, USA
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Hemm MR, Paul BJ, Schneider TD, Storz G, Rudd KE. Small membrane proteins found by comparative genomics and ribosome binding site models. Mol Microbiol 2009; 70:1487-501. [PMID: 19121005 DOI: 10.1111/j.1365-2958.2008.06495.x] [Citation(s) in RCA: 152] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The correct annotation of genes encoding the smallest proteins is one of the biggest challenges of genome annotation, and perhaps more importantly, few annotated short open reading frames have been confirmed to correspond to synthesized proteins. We used sequence conservation and ribosome binding site models to predict genes encoding small proteins, defined as having 16-50 amino acids, in the intergenic regions of the Escherichia coli genome. We tested expression of these predicted as well as previously annotated genes by integrating the sequential peptide affinity tag directly upstream of the stop codon on the chromosome and assaying for synthesis using immunoblot assays. This approach confirmed that 20 previously annotated and 18 newly discovered proteins of 16-50 amino acids are synthesized. We summarize the properties of these small proteins; remarkably more than half of the proteins are predicted to be single-transmembrane proteins, nine of which we show co-fractionate with cell membranes.
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Affiliation(s)
- Matthew R Hemm
- Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, MD 20892, USA
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Rider SD, Hemm MR, Hostetler HA, Li HC, Chapple C, Ogas J. Metabolic profiling of the Arabidopsis pkl mutant reveals selective derepression of embryonic traits. Planta 2004; 219:489-99. [PMID: 15085429 PMCID: PMC2536513 DOI: 10.1007/s00425-004-1254-1] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/19/2003] [Accepted: 02/24/2004] [Indexed: 05/21/2023]
Abstract
Embryos express several unique differentiation characteristics, including the accumulation of a number of metabolites that are generally considered to be unique to seeds. PICKLE (PKL) codes for a CHD3-chromatin remodeling factor that is necessary for repression of embryonic traits in seedlings of Arabidopsis thaliana (L.) Heynh. In pkl mutants, primary roots are capable of expressing many embryonic traits after germination and are referred to as "pickle roots". In an attempt to examine the breadth of PKL-dependent repression of embryo-specific differentiation pathways, we determined the extent to which a variety of embryo-specific compounds accumulate in pickle roots. We found that pickle roots accumulate triacylglycerol with a fatty acid composition that is similar to that found in seeds. The major seed storage proteins are also present in pickle roots. In addition to these two well-characterized seed storage compounds, we observed that pickle roots accumulate phytate, a form of stored phosphate that is preferentially accumulated in seeds. Seeds of members of the Brassicaceae also accumulate a variety of unique secondary metabolites, including sinapate esters and glucosinolates. Surprisingly, the levels of secondary metabolites in pickle roots were not suggestive of an embryonic differentiation state, but did reveal that a mutation in PKL results in substantial changes in root secondary metabolism. Taken together, these data suggest that PKL is responsible for regulating some but not all aspects of the embryonic program as it relates to the accumulation of embryo-specific metabolites.
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Affiliation(s)
- Stanley Dean Rider
- Purdue University Department of Biochemistry 175 S. University Street West Lafayette, Indiana 47907−2063
| | - Matthew R. Hemm
- Purdue University Department of Biochemistry 175 S. University Street West Lafayette, Indiana 47907−2063
| | - Heather A. Hostetler
- Purdue University Department of Animal Science 915 W. State Street West Lafayette, Indiana 47907−2054
| | - Hui-Chun Li
- Purdue University Department of Biochemistry 175 S. University Street West Lafayette, Indiana 47907−2063
| | - Clint Chapple
- Purdue University Department of Biochemistry 175 S. University Street West Lafayette, Indiana 47907−2063
| | - Joe Ogas
- Purdue University Department of Biochemistry 175 S. University Street West Lafayette, Indiana 47907−2063
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Abstract
Experiments have shown that many phenylpropanoid genes are highly expressed in light-grown Arabidopsis roots. Studies employing reporter gene constructs have indicated that the expression of these genes is localized not only to the lignifying root vasculature, but also to non-lignifying tissues, such as the root cortex, suggesting that the proteins encoded by these genes may be involved in aspects of phenylpropanoid metabolism other than lignification. Consistent with this hypothesis, roots of etiolated and soil-grown plants contain almost no soluble phenylpropanoids, but exposure to light leads to the accumulation of flavonoids, as well as high levels of coniferin and syringin (coniferyl and sinapyl-4-O-glycosides), compounds not previously reported to be accumulated in Arabidopsis. To elucidate the mechanism by which light induces root secondary metabolism, extracts of mutants defective in light perception and light responses were analyzed for phenylpropanoid content. The results of these assays showed that phytochrome (PHY)B and cryptochrome (CRY)2 are the primary photoreceptors involved in light-dependent phenylpropanoid accumulation, and that the hypocotyl elongated (HY5) transcription factor is also required for this response. The presence of phenylpropanoids in etiolated roots of cop (constitutively photomorphogenic)1, cop9, and det (de-etiolated)1 mutants indicate that the corresponding wild-type genes are required to repress root phenylpropanoid biosynthesis in the absence of light. Biochemical analysis of root cell walls and analysis of phenylpropanoid gene expression suggest that coniferin and syringin accumulation may be the result of both increased biosynthesis and decreased conversion of these compounds into other phenylpropanoid end products. Finally, our data suggest that the accumulation of coniferin, syringin, and flavonoids in Arabidopsis roots is a high-irradiance response (HIR), and suggest that comparative analysis of light- and dark-grown Arabidopsis roots may provide new insights into both phenylpropanoid biosynthesis and light signaling in plants.
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Affiliation(s)
- Matthew R Hemm
- Department of Biochemistry, Purdue University, 1516 South University Dr, West Lafayette, IN 47907-1153, USA
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Hemm MR, Ruegger MO, Chapple C. The Arabidopsis ref2 mutant is defective in the gene encoding CYP83A1 and shows both phenylpropanoid and glucosinolate phenotypes. Plant Cell 2003; 15:179-94. [PMID: 12509530 PMCID: PMC143490 DOI: 10.1105/tpc.006544] [Citation(s) in RCA: 132] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2002] [Accepted: 10/02/2002] [Indexed: 05/17/2023]
Abstract
The Arabidopsis ref2 mutant was identified in a screen for plants having altered fluorescence under UV light. Characterization of the ref2 mutants showed that they contained reduced levels of a number of phenylpropanoid pathway-derived products: sinapoylmalate in leaves, sinapoylcholine in seeds, and syringyl lignin in stems. Surprisingly, positional cloning of the REF2 locus revealed that it encodes CYP83A1, a cytochrome P450 sharing a high degree of similarity to CYP83B1, an enzyme involved in glucosinolate biosynthesis. Upon further investigation, ref2 mutants were found to have reduced levels of all aliphatic glucosinolates and increased levels of indole-derived glucosinolates in their leaves. These results show that CYP83A1 is involved in the biosynthesis of both short-chain and long-chain aliphatic glucosinolates and suggest a novel metabolic link between glucosinolate biosynthesis, a secondary biosynthetic pathway found only in plants in the order Capparales, and phenylpropanoid metabolism, a pathway found in all plants and considered essential to the survival of terrestrial plant species.
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Affiliation(s)
- Matthew R Hemm
- Department of Biochemistry, Purdue University, 175 South University Street, West Lafayette, Indiana 47907, USA
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Franke R, Hemm MR, Denault JW, Ruegger MO, Humphreys JM, Chapple C. Changes in secondary metabolism and deposition of an unusual lignin in the ref8 mutant of Arabidopsis. Plant J 2002; 30:47-59. [PMID: 11967092 DOI: 10.1046/j.1365-313x.2002.01267.x] [Citation(s) in RCA: 175] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
The end products of the phenylpropanoid pathway play important roles in plant structure and development, as well as in plant defense mechanisms against biotic and abiotic stresses. From a human perspective, phenylpropanoid pathway-derived metabolites influence both human health and the potential utility of plants in agricultural contexts. The last known enzyme of the phenylpropanoid pathway that has not been characterized is p-coumarate 3-hydroxylase (C3H). By screening for plants that fail to accumulate soluble fluorescent phenylpropanoid secondary metabolites, we have identified a number of Arabidopsis mutants that display a reduced epidermal fluorescence (ref) phenotype. We have now shown that the ref8 mutant is defective in the gene encoding C3H. Phenotypic characterization of the ref8 mutant has revealed that the lack of C3H activity in the mutant leads to diverse changes in phenylpropanoid metabolism. The ref8 mutant accumulates p-coumarate esters in place of the sinapoylmalate found in wild-type plants. The mutant also deposits a lignin formed primarily from p-coumaryl alcohol, a monomer that is at best a minor component in the lignin of other plants. Finally, the mutant displays developmental defects and is subject to fungal attack, suggesting that phenylpropanoid pathway products downstream of REF8 may be required for normal plant development and disease resistance.
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Affiliation(s)
- Rochus Franke
- Department of Biochemistry, Purdue University, West Lafayette, IN 47907-1153, USA
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Franke R, Humphreys JM, Hemm MR, Denault JW, Ruegger MO, Cusumano JC, Chapple C. The Arabidopsis REF8 gene encodes the 3-hydroxylase of phenylpropanoid metabolism. Plant J 2002; 30:33-45. [PMID: 11967091 DOI: 10.1046/j.1365-313x.2002.01266.x] [Citation(s) in RCA: 129] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
The activity of p-coumarate 3-hydroxylase (C3H) is thought to be essential for the biosynthesis of lignin and many other phenylpropanoid pathway products in plants; however, no conditions suitable for the unambiguous assay of the enzyme are known. As a result, all attempts to purify the protein and clone its corresponding gene have failed. By screening for plants that accumulate reduced levels of soluble fluorescent phenylpropanoid secondary metabolites, we have identified a number of Arabidopsis mutants that display a reduced epidermal fluorescence (ref) phenotype. Using radiotracer-feeding experiments, we have determined that the ref8 mutant is unable to synthesize caffeic acid, suggesting that the mutant is defective in a gene required for the activity or expression of C3H. We have isolated the REF8 gene using positional cloning methods, and have verified that it encodes C3H by expression of the wild-type gene in yeast. Although many previous reports in the literature have suggested that C3H is a phenolase, the isolation of the REF8 gene demonstrates that the enzyme is actually a cytochrome P450-dependent monooxygenase. Although the enzyme accepts p-coumarate as a substrate, it also exhibits significant activity towards other p-hydroxylated substrates. These data may explain the previous difficulties in identifying C3H activity in plant extracts and they indicate that the currently accepted version of the lignin biosynthetic pathway is likely to be incorrect.
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Affiliation(s)
- Rochus Franke
- Department of Biochemistry, Purdue University, West Lafayette, IN 47907-1153, USA
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Ralph J, Lapierre C, Marita JM, Kim H, Lu F, Hatfield RD, Ralph S, Chapple C, Franke R, Hemm MR, Van Doorsselaere J, Sederoff RR, O'Malley DM, Scott JT, MacKay JJ, Yahiaoui N, Boudet A, Pean M, Pilate G, Jouanin L, Boerjan W. Elucidation of new structures in lignins of CAD- and COMT-deficient plants by NMR. Phytochemistry 2001; 57:993-1003. [PMID: 11423146 DOI: 10.1016/s0031-9422(01)00109-1] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Studying lignin-biosynthetic-pathway mutants and transgenics provides insights into plant responses to perturbations of the lignification system, and enhances our understanding of normal lignification. When enzymes late in the pathway are downregulated, significant changes in the composition and structure of lignin may result. NMR spectroscopy provides powerful diagnostic tools for elucidating structures in the difficult lignin polymer, hinting at the chemical and biochemical changes that have occurred. COMT (caffeic acid O-methyl transferase) downregulation in poplar results in the incorporation of 5-hydroxyconiferyl alcohol into lignins via typical radical coupling reactions, but post-coupling quinone methide internal trapping reactions produce novel benzodioxane units in the lignin. CAD (cinnamyl alcohol dehydrogenase) downregulation results in the incorporation of the hydroxycinnamyl aldehyde monolignol precursors intimately into the polymer. Sinapyl aldehyde cross-couples 8-O-4 with both guaiacyl and syringyl units in the growing polymer, whereas coniferyl aldehyde cross-couples 8-O-4 only with syringyl units, reflecting simple chemical cross-coupling propensities. The incorporation of hydroxycinnamyl aldehyde and 5-hydroxyconiferyl alcohol monomers indicates that these monolignol intermediates are secreted to the cell wall for lignification. The recognition that novel units can incorporate into lignins portends significantly expanded opportunities for engineering the composition and consequent properties of lignin for improved utilization of valuable plant resources.
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Affiliation(s)
- J Ralph
- US Dairy Forage Research Center, USDA-Agricultural Research Service, 1925 Linden Drive West, Madison, WI 53706, USA.
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Abstract
Mounting evidence indicates that members of the large family of plant MYB proteins are involved in the transcriptional regulation of an array of metabolic and developmental processes. Recently, the Arabidopsis thaliana MYB, AtMYB4, was shown to regulate the accumulation of the UV-protectant compound sinapoylmalate by repressing the transcription of the gene encoding the phenylpropanoid enzyme cinnamate 4-hydroxylase. AtMYB4 is thus a key regulator of phenylpropanoid pathway gene expression, and is the first example of a MYB protein that functions as a transcriptional repressor.
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Affiliation(s)
- M R Hemm
- Department of Biochemistry, Purdue University, West Lafayette, IN 47907, USA
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Humphreys JM, Hemm MR, Chapple C. New routes for lignin biosynthesis defined by biochemical characterization of recombinant ferulate 5-hydroxylase, a multifunctional cytochrome P450-dependent monooxygenase. Proc Natl Acad Sci U S A 1999; 96:10045-50. [PMID: 10468559 PMCID: PMC17839 DOI: 10.1073/pnas.96.18.10045] [Citation(s) in RCA: 206] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The enzymes and genes of the lignin biosynthetic pathway have been studied for several decades, but the gene encoding ferulate 5-hydroxylase (F5H) was cloned only 3 years ago by T-DNA tagging in Arabidopsis. To characterize the enzyme in detail, we have expressed F5H in yeast. According to current models of the phenylpropanoid pathway, F5H catalyzes the hydroxylation of ferulate to 5-hydroxyferulate; however, our studies indicate that the enzyme also uses coniferaldehyde and coniferyl alcohol as substrates. Unexpectedly, the K(m) values measured for the latter two substrates are three orders of magnitude lower than that measured for ferulic acid, suggesting that in lignifying tissues, syringyl monomers may be derived from their guaiacyl counterparts by hydroxylation and subsequent methylation. Thus, F5H may function later in the lignin biosynthetic pathway than was originally proposed. To further test this model, recombinant F5H was incubated together with ferulic acid, coniferaldehyde, or coniferyl alcohol in the presence of native or recombinant Arabidopsis caffeic acid/5-hydroxyferulic acid O-methyltransferase and [(14)C]S-adenosylmethionine. In all cases, the corresponding radiolabeled sinapyl derivatives were synthesized, indicating that the necessary enzymes required for this pathway are present in Arabidopsis. Taken together, these data suggest that the previously accepted pathway for lignin biosynthesis is likely to be incorrect.
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Affiliation(s)
- J M Humphreys
- Department of Biochemistry, Purdue University, West Lafayette, IN 47907-1153, USA
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