Differential Regulation of Myelin Basic Protein Isoforms and Deiminated Isomers by Calmodulin

DURAND SANDRA E.; MAURICIO R. GALIANO; BOSC C.; MIRANDA A. L.; FRANK R.; ANDRIEUX A.; MARTA E. HALLAK

Huerta Grande, Cordoba

Congreso; XXIX Congreso Anual de la Sociedad Argentina de Investigacion en Neurociencias; 2014

Sociedad Argentina de Investigacion en Neurociencias

Myelin basic protein (MBP) plays an essential role in the formation of myelin compact membranes in central nervous system. Interactions of MBP with different cellular components are regulated by calmodulin (CaM) and by diverse post-translational modifications (PTMs) undergone by MBP. We studied the MBP-CaM interaction in the six isoforms of classic MBP by analyzing immobilized peptide arrays. We found that CaM binds to four different domains of MBP located in exons that are involved in the alternative splicing, three of which are Ca2+-dependent. In addition, these CaM-binding sites of MBP differ in the strength of interaction showing one of them twice greater strength than the others three sites. Two primary-sequence motifs (KXXK and RXXR) were identified in the amino acid sequence of the strongest CaM-binding site of MBP; these motifs in MBP are the responsible of the high strength of interaction with CaM and each motif contributes to half of this interaction strength. Besides, all the binding sites of MBP to CaM identified in this work have at least two arginines that can undergo deimination, one of the most common PTMs of MBP. Generally, replacement of arginine by citrulline in these CaM-binding sites of MBP impairs MBP-CaM interaction. In multiple sclerosis (MS) disease, the deimination of MBP has been correlated with early development, the demyelination process and disease severity. In adittion, cotransfection of cells with the cDNA of CaM and MBP1 or MBP3 or MBP4 or MBP6 variants, their respective truncated mutants in the C-terminus (ΔC), constructs that encode different combinations of CaM-binding sites, and a mutant named rmC8 constructed from MBP3 by specific R/K→Q substitutions (R: arginine, K: lysine, Q: glutamine) to study the effects of deimination showed different degree of colocalization. Further studies of the MBP regulation by CaM and PTMs undergone by MBP could help to understand its role in signaling for oligodendrocyte differentiation and myelin formation, and its involvement in the pathogenesis of MS. Supported by CONICET, FONCyT and SECyT