Unexpected ancient paralogs and an evolutionary model for the COPII coat complex

Area of Science:

• Cell Biology
• Evolutionary Biology
• Genomics

Background:

• The coat protein complex II (COPII) facilitates essential protein transport from the Endoplasmic Reticulum (ER) to the Golgi apparatus.
• COPII shares components with other vital cellular complexes, suggesting linked evolutionary origins.
• Its evolutionary history remains less explored compared to other coat complexes.

Purpose of the Study:

• To investigate the evolutionary history and distribution of COPII components across eukaryotic diversity.
• To reconstruct the ancestral COPII coat composition in the Last Eukaryotic Common Ancestor (LECA).
• To understand the evolutionary relationships between COPII and other protocoatomer-containing complexes.

Main Methods:

• Comparative genomics using homology searching across 74 eukaryotic genomes.
• Phylogenetic analyses to determine the presence and evolutionary history of COPII components.
• Identification of novel paralogs and assessment of their ancient presence and distribution.

Main Results:

• Sec12, Sec16, Sar1, Sec13, Sec31, Sec23, and Sec24 were present in the LECA; Sed4 was not.
• A previously undetected Sec23 paralog predates the archaeplastid clade.
• Three Sec24 paralogs were likely present in the LECA, including one anciently present but subsequently lost in certain lineages.

Conclusions:

• The COPII coat in the LECA was more complex than previously recognized.
• This complexity provides insights into the evolution of COPII and its relationship with other protocoatomer-derived complexes.
• The study highlights the power of comparative genomics in uncovering ancient cellular machinery evolution.