Protein prenylation in spinach chloroplasts.

Area of Science:

• Plant Biochemistry
• Molecular Biology
• Posttranslational Modifications

Background:

• Protein prenylation is a crucial posttranslational modification in eukaryotes.
• Conventional prenylation involves isoprenoid lipids attached to proteins, influencing their function.
• Understanding plant-specific prenylation mechanisms is essential for plant cell biology.

Purpose of the Study:

• To investigate the distinct pathways of protein prenylation in plants.
• To characterize the nature and origin of prenyl groups in different cellular compartments.
• To elucidate the dependence of prenylation on nuclear and plastid gene expression.

Main Methods:

• In vivo metabolic labeling with (3)H-mevalonate.
• Use of protein synthesis inhibitors to differentiate pathways.
• Gas chromatography-mass spectrometry (GC-MS) for isoprenoid identification.
• Alkaline treatment to release modifying groups from proteins.

Main Results:

• Two categories of protein prenylation were identified in spinach cotyledons.
• Conventional prenylation involves farnesyl/geranylgeranyl groups and depends on nuclear gene expression.
• A novel chloroplast-specific prenylation uses phytol, derived from farnesol/geranylgeraniol, and depends on plastid gene expression.
• Phytol linkage to chloroplast proteins does not involve a thioether bond.

Conclusions:

• Plants exhibit both conserved and unique protein prenylation mechanisms.
• Chloroplast prenylation represents a novel modification pathway distinct from conventional prenylation.
• This chloroplast-specific prenylation is linked to plastid gene expression and involves phytol modification.