title: Accumulation of altered aspartyl residues in erythrocyte membrane proteins from patients with sporadic amyotrophic lateral sclerosis.
abstract: Spontaneous protein deamidation of labile asparagines (Asn), generating abnormal l-isoaspartyl residues (IsoAsp), is associated with cell aging and enhanced by an oxidative microenvironment. The presence of isopeptide bonds impairs protein structure/function. To minimize the damage, IsoAsp can be "repaired" by the protein l-isoaspartyl/d-aspartyl O-methyltransferase (PIMT) and S-adenosylmethionine (AdoMet) is the methyl donor of this reaction. PIMT is a repair enzyme that initiates the conversion of l-isoAsp (or d-Asp) residues to l-Asp residues. Amyotrophic lateral sclerosis (ALS) is a severe neurodegenerative disease principally affecting motor neurons. The condition of oxidative stress reported in familial and sporadic forms of ALS prompted us to investigate Asn deamidation in ALS tissue. Erythrocytes (RBCs) were selected as a model system since they are unable to replace damaged proteins and protein methylesterification is virtually the only AdoMet-consuming reaction operating in these cells. Our data show that, in vitro assay, abnormal IsoAsp residues were significantly higher in ALS patients erythrocyte membrane proteins with an increased methyl accepting capability relative to controls (p<0.05). Moreover, we observed a reduction in AdoMet levels, while AdoHcy concentration was comparable to that detected in the control, resulting in a lower [AdoMet]/[AdoHcy] ratio. Then, the accumulation of altered aspartyl residues in ALS patients is probably related to a reduced efficiency of the S-adenosylmethionine (AdoMet)-dependent repair system causing increased protein instability at Asn sites. The increase of abnormal residues represents a new protein alteration that may be present not only in red blood cells but also in other cell types of patients suffering from ALS.
authors.affiliation: Department of Motor Sciences and Wellness, Parthenope University, Naples, Italy; Department of Biochemistry, Biophysics and General Pathology, Second University of Naples, Naples, Italy. Electronic address: sdangelo@uniparthenope.it.
authors.forename: Stefania
authors.initials: S
authors.lastname: D'Angelo
authors.affiliation: Department of Neurological Sciences, Second University of Naples, Naples, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Trojsi
authors.affiliation: Department of Biochemistry, Biophysics and General Pathology, Second University of Naples, Naples, Italy.
authors.forename: Anna
authors.initials: A
authors.lastname: Salvatore
authors.affiliation: Department of Neurological Sciences, Second University of Naples, Naples, Italy.
authors.forename: Luca
authors.initials: L
authors.lastname: Daniele
authors.affiliation: Department of Biochemistry, Biophysics and General Pathology, Second University of Naples, Naples, Italy.
authors.forename: Marianna
authors.initials: M
authors.lastname: Raimo
authors.affiliation: Department of Biochemistry, Biophysics and General Pathology, Second University of Naples, Naples, Italy.
authors.forename: Patrizia
authors.initials: P
authors.lastname: Galletti
authors.affiliation: Department of Neurological Sciences, Second University of Naples, Naples, Italy.
authors.forename: Maria Rosaria
authors.initials: MR
authors.lastname: Monsurrò
mesh_terms: D000328:Adult; D000368:Aged; D000690:Amyotrophic Lateral Sclerosis / Q000097:blood / Q000150:complications / Q000378:metabolism*; D001224:Aspartic Acid / Q000378:metabolism*; D004910:Erythrocyte Membrane / Q000378:metabolism*; D005260:Female; D006801:Humans; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D008715:Methionine / Q000378:metabolism; D008716:Methionine Adenosyltransferase / Q000378:metabolism; D008875:Middle Aged; D010084:Oxidation-Reduction; D018384:Oxidative Stress / Q000187:drug effects; D026601:Protein D-Aspartate-L-Isoaspartate Methyltransferase / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D012435:S-Adenosylhomocysteine
chemical_list: D008565:Membrane Proteins; D017382:Reactive Oxygen Species; D001224:Aspartic Acid; D012435:S-Adenosylhomocysteine; D008715:Methionine; C435725:PCMT1 protein, human; D026601:Protein D-Aspartate-L-Isoaspartate Methyltransferase; D008716:Methionine Adenosyltransferase
keywords: AdoHcy; AdoMet; Amyotrophic lateral sclerosis; Erythrocytes; Oxidative stress; PIMT; Protein deamidation; Protein l-isoaspartyl/d-aspartyl O-methyltransferase; S-Adenosylmethionine; S-adenosylhomocisteine; S-adenosylmethionine; protein l-isoaspartyl/d-aspartyl O-methyltransferase