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Estrada P, Bañares-Hidalgo Á, Pérez-Gil J. Disulfide bonds in the SAPA domain of the pulmonary surfactant protein B precursor. J Proteomics 2022; 269:104722. [PMID: 36108905 DOI: 10.1016/j.jprot.2022.104722] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2022] [Revised: 08/31/2022] [Accepted: 09/06/2022] [Indexed: 10/14/2022]
Abstract
The disulfide bonds formed in the SAPA domain of a recombinant version of the NH2-terminal propeptide (SP-BN) from the precursor of human pulmonary surfactant protein B (SP-B) were identified through sequential digestion of SP-BN with GluC/trypsin or thermolysin/GluC, followed by mass spectrometry (MS) analysis. MS spectra allowed identification of disulfide bonds between Cys32-Cys49 and Cys40-Cys55, and we propose a disulfide connectivity pattern of 1-3 and 2-4 within the SAPA domain, with the Cys residues numbered according to their position from the N-terminus of the propeptide sequence. The peaks with m/z ∼ 2136 and ∼ 1780 in the MS spectrum of the GluC/trypsin digest were assigned to peptides 24AWTTSSLACAQGPE37 and 45QALQCR50 linked by Cys32-Cys49 and 38FWCQSLE44 and 51ALGHCLQE58 linked by Cys40-Cys55 respectively. Tandem mass spectrometry (MS/MS) analysis verified the position of the bonds. The results of the series ions, immonium ions and internal fragment ions were all compatible with the proposed 1-3/2-4 position of the disulfide bonds in the SAPA domain. This X-pattern differs from the kringle-type found in the SAPB domain of the SAPLIP proteins, where the first Cys in the sequence links to the last, the second to the penultimate and the third to the fourth one. Regarding the SAPB domain of the SP-BN propeptide, the MS analysis of both digests identified the bond Cys100-Cys112, numbered 7-8, which is coincident with the bond position in the kringle motif. SIGNIFICANCE: The SAPLIP (saposin-like proteins) family encompasses several proteins with homology to saposins (sphingolipids activator proteins). These are proteins with mainly alpha-helical folds, compact packing including well conserved disulfide bonds and ability to interact with phospholipids and membranes. There are two types of saposin-like domains termed as Saposin A (SAPA) and Saposin B (SAPB) domains. While disulfide connectivity has been well established in several SAPB domains, the position of disulfide bonds in SAPA domains is still unknown. The present study approaches a detailed proteomic study to determine disulfide connectivity in the SAPA domain of the precursor of human pulmonary surfactant-associated protein SP-B. This task has been a challenge requiring the combination of different sequential proteolytic treatments followed by MS analysis including MALDI-TOF and tandem mass MS/MS spectrometry. The determination for first time of the position of disulfide bonds in SAPA domains is an important step to understand the structural determinants defining its biological functions.
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Affiliation(s)
- Pilar Estrada
- Dept. Biochemistry and Molecular Biology, Faculty of Biology, Complutense University, 28040 Madrid, Spain
| | - Ángeles Bañares-Hidalgo
- Dept. Biochemistry and Molecular Biology, Faculty of Biology, Complutense University, 28040 Madrid, Spain
| | - Jesús Pérez-Gil
- Dept. Biochemistry and Molecular Biology, Faculty of Biology, Complutense University, 28040 Madrid, Spain.
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Li J, Hu S, Jian W, Xie C, Yang X. Plant antimicrobial peptides: structures, functions, and applications. BOTANICAL STUDIES 2021; 62:5. [PMID: 33914180 PMCID: PMC8085091 DOI: 10.1186/s40529-021-00312-x] [Citation(s) in RCA: 86] [Impact Index Per Article: 28.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2021] [Accepted: 04/13/2021] [Indexed: 05/20/2023]
Abstract
Antimicrobial peptides (AMPs) are a class of short, usually positively charged polypeptides that exist in humans, animals, and plants. Considering the increasing number of drug-resistant pathogens, the antimicrobial activity of AMPs has attracted much attention. AMPs with broad-spectrum antimicrobial activity against many gram-positive bacteria, gram-negative bacteria, and fungi are an important defensive barrier against pathogens for many organisms. With continuing research, many other physiological functions of plant AMPs have been found in addition to their antimicrobial roles, such as regulating plant growth and development and treating many diseases with high efficacy. The potential applicability of plant AMPs in agricultural production, as food additives and disease treatments, has garnered much interest. This review focuses on the types of plant AMPs, their mechanisms of action, the parameters affecting the antimicrobial activities of AMPs, and their potential applications in agricultural production, the food industry, breeding industry, and medical field.
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Affiliation(s)
- Junpeng Li
- College of Life Science, Chongqing Normal University, Chongqing, 401331, China
| | - Shuping Hu
- College of Life Science, Chongqing Normal University, Chongqing, 401331, China
| | - Wei Jian
- College of Life Science, Chongqing Normal University, Chongqing, 401331, China
| | - Chengjian Xie
- College of Life Science, Chongqing Normal University, Chongqing, 401331, China.
| | - Xingyong Yang
- College of Life Science, Chongqing Normal University, Chongqing, 401331, China.
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Dupuis JH, Wang S, Song C, Yada RY. The role of disulfide bonds in a Solanum tuberosum saposin-like protein investigated using molecular dynamics. PLoS One 2020; 15:e0237884. [PMID: 32841243 PMCID: PMC7447066 DOI: 10.1371/journal.pone.0237884] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2020] [Accepted: 08/04/2020] [Indexed: 01/31/2023] Open
Abstract
The Solanum tuberosum plant specific insert (StPSI) has a defensive role in potato plants, with the requirements of acidic pH and anionic lipids. The StPSI contains a set of three highly conserved disulfide bonds that bridge the protein’s helical domains. Removal of these bonds leads to enhanced membrane interactions. This work examined the effects of their sequential removal, both individually and in combination, using all-atom molecular dynamics to elucidate the role of disulfide linkages in maintaining overall protein tertiary structure. The tertiary structure was found to remain stable at both acidic (active) and neutral (inactive) pH despite the removal of disulfide linkages. The findings include how the dimer structure is stabilized and the impact on secondary structure on a residue-basis as a function of disulfide bond removal. The StPSI possesses an extensive network of inter-monomer hydrophobic interactions and intra-monomer hydrogen bonds, which is likely the key to the stability of the StPSI by stabilizing local secondary structure and the tertiary saposin-fold, leading to a robust association between monomers, regardless of the disulfide bond state. Removal of disulfide bonds did not significantly impact secondary structure, nor lead to quaternary structural changes. Instead, disulfide bond removal induces regions of amino acids with relatively higher or lower variation in secondary structure, relative to when all the disulfide bonds are intact. Although disulfide bonds are not required to preserve overall secondary structure, they may have an important role in maintaining a less plastic structure within plant cells in order to regulate membrane affinity or targeting.
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Affiliation(s)
- John H. Dupuis
- Food, Nutrition, and Health Program, Faculty of Land and Food Systems, University of British Columbia, Vancouver, British Columbia, Canada
| | - Shenlin Wang
- College of Chemistry and Molecular Engineering and Beijing NMR Center, Peking University, Beijing, People's Republic of China
| | - Chen Song
- Center for Quantitative Biology, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, People’s Republic of China
| | - Rickey Y. Yada
- Food, Nutrition, and Health Program, Faculty of Land and Food Systems, University of British Columbia, Vancouver, British Columbia, Canada
- * E-mail:
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4
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Bañares-Hidalgo Á, Pérez-Gil J, Estrada P. Conformational Stability of the NH2-Terminal Propeptide of the Precursor of Pulmonary Surfactant Protein SP-B. PLoS One 2016; 11:e0158430. [PMID: 27380171 PMCID: PMC4933373 DOI: 10.1371/journal.pone.0158430] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2016] [Accepted: 06/15/2016] [Indexed: 11/18/2022] Open
Abstract
Assembly of pulmonary surfactant lipid-protein complexes depends on conformational changes coupled with proteolytic maturation of proSP-B, the precursor of pulmonary surfactant protein B (SP-B), along the surfactant biogenesis pathway in pneumocytes. Conformational destabilization of the N-terminal propeptide of proSP-B (SP-BN) triggers exposure of the mature SP-B domain for insertion into surfactant lipids. We have studied the conformational stability during GdmCl- or urea-promoted unfolding of SP-BN with trp fluorescence and circular dichroism spectroscopies. Binding of the intermediate states to bis-ANS suggests their molten globule-like character. ΔG0H2O was ~ 12.7 kJ·mol-1 either with urea or GdmCl. None of the thermal transitions of SP-BN detected by CD correspond to protein unfolding. Differential scanning calorimetry of SP-BN evidenced two endothermic peaks involved in oligomer dissociation as confirmed with 2 M urea. Ionic strength was relevant since at 150 mM NaCl, the process originating the endotherm at the highest temperature was irreversible (Tm2 = 108.5°C) with an activation energy of 703.8 kJ·mol-1. At 500 mM NaCl the process became reversible (Tm2 = 114.4°C) and data were fitted to the Non-two States model with two subpeaks. No free thiols in the propeptide could be titrated by DTNB with or without 5.7 M GdmCl, indicating disulfide bonds establishment.
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Affiliation(s)
- Ángeles Bañares-Hidalgo
- Departamento de Bioquímica y Biología Molecular I, Facultad de Biología, Universidad Complutense, Ciudad Universitaria, 28040, Madrid, Spain
| | - Jesús Pérez-Gil
- Departamento de Bioquímica y Biología Molecular I, Facultad de Biología, Universidad Complutense, Ciudad Universitaria, 28040, Madrid, Spain
| | - Pilar Estrada
- Departamento de Bioquímica y Biología Molecular I, Facultad de Biología, Universidad Complutense, Ciudad Universitaria, 28040, Madrid, Spain
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Wengier DL, Mazzella MA, Salem TM, McCormick S, Muschietti JP. STIL, a peculiar molecule from styles, specifically dephosphorylates the pollen receptor kinase LePRK2 and stimulates pollen tube growth in vitro. BMC PLANT BIOLOGY 2010; 10:33. [PMID: 20175921 PMCID: PMC2844069 DOI: 10.1186/1471-2229-10-33] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/11/2009] [Accepted: 02/22/2010] [Indexed: 05/06/2023]
Abstract
BACKGROUND LePRK1 and LePRK2 are two pollen receptor kinases localized to the plasma membrane, where they are present in a high molecular weight complex (LePRK complex). LePRK2 is phosphorylated in mature and germinated pollen, but is dephosphorylated when pollen membranes are incubated with tomato or tobacco style extracts. RESULTS Here we show that LePRK2 dephosphorylation is mediated by a heat-, acid-, base-, DTT- and protease-resistant component from tobacco styles. Using LePRK2 phosphorylation as a tracking assay for purification, style exudates were subjected to chloroform extraction, anionic exchange, and C18 reverse-phase chromatography columns. We finally obtained a single ~3,550 Da compound (as determined by UV-MALDI-TOF MS) that we named STIL (for Style Interactor for LePRKs). STIL increased pollen tube lengths of in vitro germinated pollen in a dose-dependent manner. CONCLUSION We propose that the LePRK complex perceives STIL, resulting in LePRK2 dephosphorylation and an increase in pollen tube growth.
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Affiliation(s)
- Diego L Wengier
- Instituto de Ingeniería Genética y Biología Molecular (INGEBI), CONICET, Vuelta de Obligado 2490, 1428 Buenos Aires, Argentina
| | - María A Mazzella
- Instituto de Ingeniería Genética y Biología Molecular (INGEBI), CONICET, Vuelta de Obligado 2490, 1428 Buenos Aires, Argentina
| | - Tamara M Salem
- Instituto de Ingeniería Genética y Biología Molecular (INGEBI), CONICET, Vuelta de Obligado 2490, 1428 Buenos Aires, Argentina
| | - Sheila McCormick
- Plant Gene Expression Center, United States Department of Agriculture/Agricultural Research Service, 800 Buchanan Street, Albany, California 94710, USA
- Department of Plant and Microbial Biology, University of California at Berkeley, Berkeley, California 94720, USA
| | - Jorge P Muschietti
- Instituto de Ingeniería Genética y Biología Molecular (INGEBI), CONICET, Vuelta de Obligado 2490, 1428 Buenos Aires, Argentina
- Departamento de Fisiología y Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina
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Production of a recombinant form of the propeptide NH2-terminal of the precursor of pulmonary surfactant protein B. Enzyme Microb Technol 2006. [DOI: 10.1016/j.enzmictec.2005.10.042] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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7
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Norris AJ, Whitelegge JP, Yaghoubian A, Alattia JR, Privé GG, Toyokuni T, Sun H, Brooks MN, Panza L, Matto P, Compostella F, Remmel N, Klingenstein R, Sandhoff K, Fluharty C, Fluharty A, Faull KF. A novel mass spectrometric assay for the cerebroside sulfate activator protein (saposin B) and arylsulfatase A. J Lipid Res 2005; 46:2254-64. [PMID: 16061947 DOI: 10.1194/jlr.m500188-jlr200] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A mass spectrometric method is described for monitoring cerebrosides in the presence of excess concentrations of alkali metal salts. This method has been adapted for use in the assay of arylsulfatase A (ASA) and the cerebroside sulfate activator protein (CSAct or saposin B). Detection of the neutral glycosphingolipid cerebroside product was achieved via enhancement of ionization efficiency in the presence of lithium ions. Assay samples were extracted into the chloroform phase as for the existing assays, dried, and diluted in methanol-chloroform-containing lithium chloride. Samples were analyzed by electrospray ionization mass spectrometry with a triple quadrupole mass spectrometer in the multiple reaction monitoring tandem mass spectrometric mode. The assay has been used to demonstrate several previously unknown or ambiguous aspects of the coupled ASA/CSAct reaction, including an absolute in vitro preference for CSAct over the other saposins (A, C, and D) and a preference for the non-hydroxylated species of the sulfatide substrate over the corresponding hydroxylated species. The modified assay for the coupled ASA/CSAct reaction could find applicability in settings in which the assay could not be performed previously because of the need for radiolabeled substrate, which is now not required.
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Affiliation(s)
- Andrew J Norris
- Pasarow Mass Spectrometry Laboratory, Department of Psychiatry, and Neuropsychiatric Institute, University of California Los Angeles, Los Angeles, CA 90024, USA.
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Lansmann S, Schuette CG, Bartelsen O, Hoernschemeyer J, Linke T, Weisgerber J, Sandhoff K. Human acid sphingomyelinase. EUROPEAN JOURNAL OF BIOCHEMISTRY 2003; 270:1076-88. [PMID: 12631268 DOI: 10.1046/j.1432-1033.2003.03435.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Human acid sphingomyelinase (haSMase, EC 3.1.4.12) catalyzes the lysosomal degradation of sphingomyelin to ceramide and phosphorylcholine. An inherited haSMase deficiency leads to Niemann-Pick disease, a severe sphingolipid storage disorder. The enzyme was purified and cloned over 10 years ago. Since then, only a few structural properties of haSMase have been elucidated. For understanding of its complex functions including its role in certain signaling and apoptosis events, complete structural information about the enzyme is necessary. Here, the identification of the disulfide bond pattern of haSMase is reported for the first time. Functional recombinant enzyme expressed in SF21 cells using the baculovirus expression system was purified and digested by trypsin. MALDI-MS analysis of the resulting peptides revealed the four disulfide bonds Cys120-Cys131, Cys385-Cys431, Cys584-Cys588 and Cys594-Cys607. Two additional disulfide bonds (Cys221-Cys226 and Cys227-Cys250) which were not directly accessible by tryptic cleavage, were identified by a combination of a method of partial reduction and MALDI-PSD analysis. In the sphingolipid activator protein (SAP)-homologous N-terminal domain of haSMase, one disulfide bond was assigned as Cys120-Cys131. The existence of two additional disulfide bridges in this region was proved, as was expected for the known disulfide bond pattern of SAP-type domains. These results support the hypothesis that haSMase possesses an intramolecular SAP-type activator domain as predicted by sequence comparison [Ponting, C.P. (1994) Protein Sci., 3, 359-361]. An additional analysis of haSMase isolated from human placenta shows that the recombinant and the native human protein possess an identical disulfide structure.
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Affiliation(s)
- Stephanie Lansmann
- Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn, Germany
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9
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Ahn VE, Faull KF, Whitelegge JP, Higginson J, Fluharty AL, Privé GG. Expression, purification, crystallization, and preliminary X-ray analysis of recombinant human saposin B. Protein Expr Purif 2003; 27:186-93. [PMID: 12510003 DOI: 10.1016/s1046-5928(02)00597-1] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Saposin B (also known as cerebroside sulfate activator or CSAct) is a small non-enzymatic glycoprotein required for the breakdown of cerebroside sulfates (sulfatides) in lysosomes. Saposin B contains three intramolecular disulfide bridges, exists as a dimer and is remarkably heat, protease, and pH stable. We have expressed the protein in a thioredoxin reductase deficient strain of Escherichia coli and purified the protein by heat treatment, followed by ion-exchange, gel filtration, and hydrophobic interaction chromatographies. The protein is properly folded as judged by the observed disulfide bond topology, the hydrogen-deuterium exchange rate, and the level of stimulation of sulfatide hydrolysis by arylsulfatase A. Crystals of human saposin B were grown by vapor diffusion and diffract to a resolution of 2.2A. Despite obtaining only merohedrally twinned P3(1) native crystals, an untwined seleomethionine-substituted crystal belonging to space group P3(1)21 was also grown. The three-dimensional structure of saposin B protein will provide insights into how this 79 amino acid protein is able to solubilize relatively large membrane-bound lipid ligands.
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Affiliation(s)
- Victoria E Ahn
- Department of Medical Biophysics, University of Toronto, 610 University Avenue, Toronto, Ont., Canada M5G 2M9
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Friedman M. Application of the S-pyridylethylation reaction to the elucidation of the structures and functions of proteins. JOURNAL OF PROTEIN CHEMISTRY 2001; 20:431-53. [PMID: 11760118 DOI: 10.1023/a:1012558530359] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Cysteine (Cys) and cystine residues in proteins are unstable under conditions used for acid hydrolysis of peptide bonds. To overcome this problem, we proposed the use of the S-pyridylethylation reaction to stabilize Cys residues as pyridylethyl-cysteine (PEC) protein derivatives. This suggestion was based on our observation that two synthetic derivatives formed by pyridylethylation of the SH group of Cys with either 2-vinylpyridine (2-VP) or 4-vinylpyridine (4-VP), designated as S-beta-(2-pyridylethyl)-L-cysteine (2-PEC) and S-beta-(4-pyridylethyl)-L-cysteine (4-PEC), were stable under acid conditions used to hydrolyze proteins. This was also the case for protein-bound PEC groups. Since their discovery over 30 years ago, pyridylethylation reactions have been widely modified and automated for the analysis of many structurally different proteins at levels as low as 20 picomoles, to determine the primary structures of proteins and to define the influence of SH groups and disulfide bonds on the structures and functional, enzymatic, medical, nutritional, pharmacological, and toxic properties of proteins isolated from plant, microbial, marine, animal, and human sources. Pyridylethylation has been accepted as the best method for the modification of Cys residues in proteins for subsequent analysis and sequence determination. The reaction has also been proposed to measure D-Cys, homocysteine, glutathione, tryptophan, dehydroalanine, and furanthiol food flavors. This integrated overview of the diverse literature on these reactions emphasizes general concepts. It is intended to serve as a resource and guide for further progress based on the reported application of pyridylethylation reactions to more than 150 proteins.
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Affiliation(s)
- M Friedman
- Western Regional Research Center, Agricultural Research Service, USDA, Albany, CA 94710, USA.
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Fluharty CB, Johnson J, Whitelegge J, Faull KF, Fluharty AL. Comparative lipid binding study on the cerebroside sulfate activator (saposin B). J Neurosci Res 2001; 63:82-9. [PMID: 11169617 DOI: 10.1002/1097-4547(20010101)63:1<82::aid-jnr10>3.0.co;2-d] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Cerebroside sulfate activator (saposin B) is a small protein involved in glycosphingolipid metabolism. It binds certain membrane lipids, making them available to water-soluble enzymes. Defects in this protein are responsible for a form of metachromatic leukodystropy, a progressive neurodegenerative condition. The protein participates in the catabolism of a number of lipids but does show lipid binding selectivity. However, the basis of this selectivity is unclear. Here we assess the relative binding of a number of lipids compared to cerebroside sulfate (sulfatide). We utilize a competitive binding paradigm, in which the lipids compete for protein under favorable conditions and are then switched to a condition in which the complex is stable. This study is unique in that a single molecular species of the activator is employed, and an expanded selection of natural and semisynthetic membrane lipids is surveyed. No simple "binding rule" can be ascertained from these data, but ligands with longer and/or more complex lipoidal and polar adducts appear to be favored.
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Affiliation(s)
- C B Fluharty
- Mental Retardation Research Center, University of California-Los Angeles, Los Angeles, CA, USA
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12
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Whitelegge JP, Penn B, To T, Johnson J, Waring A, Sherman M, Stevens RL, Fluharty CB, Faull KF, Fluharty AL. Methionine oxidation within the cerebroside-sulfate activator protein (CSAct or Saposin B). Protein Sci 2000; 9:1618-30. [PMID: 11045609 PMCID: PMC2144706 DOI: 10.1110/ps.9.9.1618] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
The cerebroside-sulfate activator protein (CSAct or Saposin B) is a small water-soluble glycoprotein that plays an essential role in the metabolism of certain glycosphingolipids, especially sulfatide. Deficiency of CSAct in humans leads to sulfatide accumulation and neurodegenerative disease. CSAct activity can be measured in vitro by assay of its ability to activate sulfatide-sulfate hydrolysis by arylsulfatase A. CSAct has seven methionine residues and a mass of 8,845 Da when deglycosylated. Mildly oxidized, deglycosylated CSAct (+16 Da), separated from nonoxidized CSAct by reversed-phase high-performance liquid chromatography (RP-HPLC), showed significant modulation of the in vitro activity. Because oxidation partially protected against CNBr cleavage and could largely be reversed by treatment with dithiothreitol, it was concluded that the major modification was conversion of a single methionine to its sulfoxide. High-resolution RP-HPLC separated mildly oxidized CSAct into seven or more different components with shorter retention times than nonoxidized CSAct. Mass spectrometry showed these components to have identical mass (+16 Da). The shorter retention times are consistent with increased polarity accompanying oxidation of surface-exposed methionyl side chains, in general accordance with the existing molecular model. A mass-spectrometric CNBr mapping protocol allowed identification of five of the seven possible methionine-sulfoxide CSAct oxoforms. The most dramatic suppression of activity occurred upon oxidation of Met61 (26% of control) with other residues in the Q60MMMHMQ66 motif falling in the 30-50% activity range. Under conditions of oxidative stress, accumulation of minimally oxidized CSAct protein in vivo could perturb metabolism of sulfatide and other glycosphingolipids. This, in turn, could contribute to the onset and progression of neurodegenerative disease, especially in situations where the catabolism of these materials is marginal.
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Affiliation(s)
- J P Whitelegge
- Pasarow Mass Spectrometry Laboratory, University of California, Los Angeles 90095, USA.
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