Studies of posttranslational modifications in spiny dogfish myelin basic protein

Area of Science:

• Biochemistry
• Neuroscience
• Protein Chemistry

Background:

• Mammalian myelin basic protein (MBP) is known to undergo extensive posttranslational modifications, leading to charge isomers.
• Understanding these modifications in nonmammalian species provides insights into protein evolution and function.

Purpose of the Study:

• To investigate the presence and nature of charge isomers in nonmammalian MBP, specifically from dogfish.
• To compare the posttranslational modifications and resulting properties of dogfish MBP with those of mammalian MBP.

Main Methods:

• Isolation and characterization of four charge isomer components from dogfish MBP.
• Analysis of modifications including phosphorylation and deamidation.
• Electrophoretic analysis (basic pH gel electrophoresis) to compare mobility with mammalian MBP.
• Amino acid residue analysis.

Main Results:

• Four charge isomer components (C1, C2, C3, and C8) were isolated from dogfish MBP.
• Phosphorylation and deamidation were identified as key modifications.
• Dogfish MBP demonstrated lower cationicity and approximately 50% reduced electrophoretic mobility compared to human and bovine MBP.
• Phosphorylation sites were identified on serine residues in components C1 and C3.
• Component C2 contained two or three phosphate groups on specific residues.
• A discrepancy was found regarding amino acid residue 30 in dogfish MBP (lysine instead of glutamate).

Conclusions:

• Nonmammalian MBP, exemplified by dogfish, does possess charge isomers arising from posttranslational modifications.
• Phosphorylation significantly impacts the charge and electrophoretic mobility of dogfish MBP, contributing to its reduced cationicity.
• These findings highlight differences in MBP posttranslational modification patterns between mammalian and nonmammalian species.