Complex protein targeting to dinoflagellate plastids

Area of Science:

• Cell Biology
• Molecular Biology
• Algal Biology

Background:

• Protein trafficking to plastids relies on N-terminal targeting peptides.
• Secondary plastids in some organisms require signal peptides fused to transit peptides.
• Dinoflagellate algae exhibit unusual protein targeting sequences compared to other species.

Purpose of the Study:

• To identify and characterize targeting presequences of plastid proteins in the dinoflagellate Heterocapsa triquetra.
• To investigate the diversity and features of protein targeting sequences in dinoflagellates.
• To understand the mechanisms of protein trafficking to dinoflagellate plastids.

Main Methods:

• Expressed Sequence Tag (EST) survey of Heterocapsa triquetra.
• Bioinformatic analysis of identified targeting presequences.
• Comparative analysis of transit peptide classes and motifs.

Main Results:

• Identified numerous nuclear-encoded plastid protein targeting presequences in H. triquetra.
• All sequences possessed a canonical N-terminal signal peptide, typical of secondary plastid-containing organisms.
• Two distinct classes of transit peptides were discovered: one with a hydrophobic stop-transfer domain and one without.
• A conserved phenylalanine-based motif was identified in H. triquetra transit peptides.

Conclusions:

• Dinoflagellates possess a unique dual system for protein targeting to plastids, indicated by the two transit peptide classes.
• The presence of a hydrophobic domain suggests a potential role in endoplasmic reticulum membrane anchoring.
• The findings imply distinct protein trafficking routes may operate in dinoflagellate plastid import.
• The conserved phenylalanine motif represents an ancient evolutionary feature of plastid targeting peptides.