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Published on: August 29, 2018
Betaine-homocysteine methyltransferase is a developmentally regulated enzyme crystallin in rhesus monkey lens
1Laboratory of Mechanisms of Ocular Diseases, National Eye Institute, National Institutes of Health, Bethesda, Maryland 20892-2735, USA.
Abstract:
We describe herein the characterization of a major 45-kDa protein from the soluble betaH-crystallin fraction of rhesus monkey (Macaca mulatta) lens. Based on partial peptide sequence, immunoreactivity, and enzymatic activity, this protein has been identified as betaine-homocysteine S-methyltransferase (BHMT: EC 2.1.1.5), an enzyme that catalyzes the methylation of homocysteine using either betaine or thetins as methyl donors. This protein was found to be expressed abundantly in the nuclear region of the monkey lens, reaching approximately 10% of the total nuclear protein, but was barely detectable in the epithelium and cortex regions of the lens. Because the nucleus represents the early embryonic and fetal stages of lens development, we infer that BHMT expression in the lens of the eye is developmentally regulated. By virtue of its high abundance, BHMT can be considered an enzyme crystallin (psi-crystallin). This is the first enzyme crystallin to be found in primate lenses.
Insights
Researchers identified betaine-homocysteine S-methyltransferase (BHMT) as a major protein in rhesus monkey lenses. This enzyme crystallin is abundant in the lens nucleus, suggesting developmental regulation.
Area of Science:
- Ophthalmology
- Biochemistry
- Molecular Biology
Background:
- The lens crystallin fraction contains structural and functional proteins.
- Enzyme crystallins (psi-crystallins) are enzymes that have adopted structural roles in the lens.
Purpose of the Study:
- To characterize a major 45-kDa protein in the soluble betaH-crystallin fraction of rhesus monkey lenses.
- To identify the function and expression pattern of this protein within the lens.
Main Methods:
- Protein characterization using partial peptide sequencing.
- Immunoreactivity assays.
- Enzymatic activity assays.
- Western blot analysis for regional expression.
Main Results:
- A 45-kDa protein was identified as betaine-homocysteine S-methyltransferase (BHMT).
- BHMT catalyzes homocysteine methylation, utilizing betaine or thetins as methyl donors.
- BHMT is highly abundant (approx. 10% of nuclear protein) in the monkey lens nucleus but scarce in other regions.
- BHMT expression is developmentally regulated, being concentrated in early developmental stages (nucleus).
Conclusions:
- BHMT is a novel enzyme crystallin (psi-crystallin) found in primate lenses.
- Its abundance and localization suggest a significant role beyond enzymatic activity in the lens nucleus.
- This finding expands the known diversity of crystallins and their functions in the primate eye.
