Phosphorylated and nonphosphorylated epitopes of the La/SSB autoantigen: comparison of their antigenic and conformational characteristics.
La/SSB phosphoprotein is the target antigen of autoantibodies in sera of patients with Sjögren's syndrome (SS) and systemic lupus erythematosus (SLE). Among other structural and function motifs, four phosphorylation sites are encompassed in the primary sequence of La/SSB. Two of them (Thr-362 and Ser-366) are located within GSGKGKVQFQGKKTKFASDD (346-368) and one (Thr-302) within VTWEVLEGEVEKEALKKI (301-318), which are main B-cell epitopes of La/SSB. With the aim to investigate how phosphorylation, one of the most common posttranslational protein modifications, affects the antigenic and conformational characteristics of the La/SSB epitopes, we synthesized and studied the phosphorylated epitopes La/SSB(346-368)-P, La/SSB(359-368)-P, and La/SSB(301-318)-P with respect to their nonphosphorylated counterparts. Anti-La/SSB positive sera from SS and SLE patients are better recognized by the phosphorylated epitopes compared to their nonphosphorylated counterparts. Conformational analysis by (1)H nuclear magnetic resonance spectroscopy and molecular dynamics showed that the phosphorylated epitopes adopt different structural characteristics from those of the corresponding nonphosphorylated epitopes. It is concluded that phosphorylation can create neoepitopes with altered functions, compared to the nonphosphorylated epitopes, which might be seen from the immune system as "foreign."
Coudevylle
Nicolas
N
Laboratoire de Chimie-Physique Macromoléculaire, UMR 7568 CNRS-INPL, Groupe ENSIC, Nancy, France.
Rokas
Dimitrios
D
Sakarellos-Daitsiotis
Maria
M
Krikorian
Dimitrios
D
Panou-Pomonis
Eugenia
E
Sakarellos
Constantinos
C
Boussard
Guy
G
Cung
Manh Thong
MT
D000595:Amino Acid Sequence; D001324:Autoantigens / Q000737:chemistry / Q000145:classification / Q000276:immunology*; D003198:Computer Simulation; D004797:Enzyme-Linked Immunosorbent Assay; D000939:Epitopes / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D006367:HeLa Cells; D006801:Humans; D006860:Hydrogen Bonding; D008180:Lupus Erythematosus, Systemic / Q000097:blood / Q000276:immunology; D013058:Mass Spectrometry; D018613:Microscopy, Confocal; D008958:Models, Molecular; D008968:Molecular Conformation; D008970:Molecular Weight; D019906:Nuclear Magnetic Resonance, Biomolecular; D010455:Peptides / Q000235:genetics / Q000276:immunology; D010766:Phosphorylation; D012261:Ribonucleoproteins / Q000737:chemistry / Q000145:classification / Q000276:immunology*; D012859:Sjogren's Syndrome / Q000097:blood / Q000276:immunology; D021241:Spectrometry, Mass, Electrospray Ionization; D000097585:SS-B Antigen
D001324:Autoantigens; D000939:Epitopes; D010455:Peptides; D012261:Ribonucleoproteins; D000097585:SS-B Antigen