beta-Hydroxyaspartic acid in vitamin K-dependent protein C

Area of Science:

• Biochemistry
• Protein Chemistry
• Structural Biology

Background:

• The light chain of protein C, an anticoagulant plasma protein, was previously noted to contain an unusual amino acid.
• The specific identity and structure of this amino acid were not determined.

Purpose of the Study:

• To determine the structure of the unusual amino acid found in the light chain of protein C.
• To elucidate the stereochemistry of the identified amino acid.

Main Methods:

• Isolation of a heptapeptide (residues 69-75) from enzymatic digests of protein C's light chain.
• Utilized automatic Edman sequence analysis, 1H NMR spectroscopy, and mass spectrometry for structural determination.
• Analyzed acid and aminopeptidase M hydrolysates to confirm stereochemistry.

Main Results:

• The heptapeptide was identified as containing beta-hydroxyaspartic acid at position 71 of the protein C light chain.
• The beta-hydroxyaspartic acid was confirmed to be the erythro form.
• Acid hydrolysis of protein C yielded approximately one mole of beta-hydroxyaspartic acid per mole of protein.

Conclusions:

• The novel amino acid erythro-beta-hydroxyaspartic acid has been identified in the light chain of protein C.
• This amino acid has not been previously reported in other proteins.
• The functional significance of erythro-beta-hydroxyaspartic acid in protein C is currently unknown.