Deimination of Myelin Basic Protein. 1. Effect of Deimination of Arginyl Residues of Myelin Basic Protein on Its Structure and Susceptibility to Digestion by Cathepsin D

Abstract

The effect of deimination of arginyl residues in bovine myelin basic protein (MBP) on its susceptibility to digestion by cathepsin D has been studied. Using bovine component 1 (C-1) of MBP, the most unmodified of the components with all 18 arginyl residues intact, we have generated a number of citrullinated forms by treatment of the protein with purified peptidylarginine deiminase (PAD) in vitro. We obtained species containing 0-9.9 mol of citrulline/mol of MBP. These various species were digested with cathepsin D, a metalloproteinase which cleaves proteins at Phe-Phe linkages. The rate of digestion compared to component 1 was only slightly affected when 2.7 or 3.8 mol of citrulline/mol of MBP was present. With 7.0 mol of citrulline/mol of MBP, a large increase in the rate of digestion occurred. No further increase was observed with 9.9 mol of citrulline/mol of MBP. The immunodominant peptide 43-88 (bovine sequence) was released slowly when 2.7 and 3.8 mol of citrulline/mol of MBP was present, but it was released rapidly when 7.0 mol of citrulline/mol of MBP was present. The dramatic change in digestion with 7.0 mol of citrulline/mol of MBP or more could be explained by a change in three-dimensional structure. Molecular dynamics simulation showed that increasing the number of citrullinyl residues above 7 mol/mol of MBP generated a more open structure, consistent with experimental observations in the literature. We conclude that PAD, which deiminates arginyl residues in proteins, decreases both the charge and compact structure of MBP. This structural change allows better access of the Phe-Phe linkages to cathepsin D. This scheme represents an effective way of generating the immunodominant peptide which sensitizes T-cells for the autoimmune response in demyelinating disease.

Accumulation of Citrullinated Proteins by Up-Regulated Peptidylarginine Deiminase 2 in Brains of Scrapie-Infected Mice

“…8 The expression level of GFAP was increased in every brain region tested; in contrast, there was a marked decrease in MBP in all regions except cerebellum ( Figure 8). These results may reflect the unfolding of citrullinated MBP and subsequent rapid degradation by cathepsin D, 37 an enzyme that is increased in scrapie. 38 A decrease of MBP may evoke demyelinating changes in prion diseases.…”

Peptidylarginine deiminase and protein citrullination in prion diseases

“…33 A biochemical study revealed that the rates of digestion of human MBPs containing 6 citrulline residues and 18 citrulline residues by cathepsin D were 4-fold and 45-fold, respectively, more rapid than the rate of digestion of non-citrullinated MBP. 37 Increasing the number of citrulline residues in MBP results in a more open conformation, decreases the charge and allows better access of the Phe-Phe linkages to cathepsin D, 38 thus, yielding much less compact protein-lipid complexes leading to a looser structure of the myelin sheath. 39 It is currently hypothesized that citrullinated MBP is involved in an important novel pathway in the pathogenesis of MS. 37 …”

Increased Citrullination of Histone H3 in Multiple Sclerosis Brain and Animal Models of Demyelination: A Role for Tumor Necrosis Factor-Induced Peptidylarginine Deiminase 4 Translocation

“…The identity and mechanisms of processes generating disease progression and new lesions with failures of remission and regeneration remain unknown . We previously proposed that myelin damage in MS white matter results from a failure to maintain compact adult myelin reflecting abnormally enhanced citrullination of myelin basic protein (MBP), because these less cationic MBP isomers are unable to stabilize myelin multilayers (Moscarello et al, 1994) and are more susceptible to digestion by proteases (Pritzker et al, 2000).…”