Alpha B- and βA3-crystallins containing d-aspartic acids exist in a monomeric state

Area of Science:

• Ophthalmology
• Biochemistry
• Protein Chemistry

Background:

• Eye lens transparency relies on crystallin stability and interactions.
• Lens crystallins (α-, β-, γ-) undergo age-related post-translational modifications.
• Racemization/isomerization of aspartyl residues is known in α- and β-crystallins but not γ-crystallins.

Purpose of the Study:

• Investigate aspartate (Asp) residue racemization and isomerization in the γ-crystallin fraction of elderly donors.
• Determine if Asp residue stereoinversion affects αB- and βA3-crystallin assembly in aged human lenses.

Main Methods:

• Analysis of γ-crystallin fractions from elderly donors.
• Investigated Asp residue racemization and isomerization.
• Fractionation of lens proteins by molecular weight.
• Assessed stereoinversion of Asp-96 in αB-crystallin and Asp-37 in βA3-crystallin.

Main Results:

• Asp residues in γS-, γD-, and γC-crystallins showed no racemization or isomerization.
• αB-crystallin and βA3-crystallin were found in lower molecular weight fractions.
• High stereoinversion of Asp-96 (αB-crystallin) and Asp-37 (βA3-crystallin) was observed in these lower molecular weight fractions.
• Stereoinversion did not occur in native higher molecular weight fractions.

Conclusions:

• Asp residue stereoinversion in αB- and βA3-crystallins may lead to their dissociation from polymeric and oligomeric states.
• This stereoinversion of amino acids potentially disrupts lens protein assembly in aged human lenses.
• First report linking amino acid stereoinversion to lens protein assembly disturbance.