Small viruses reveal bidirectional evolution between HK97-fold viruses and encapsulins via procapsids.

Small HK97-fold viral genomes linked to procapsids suggest bidirectional evolution between viruses and encapsulins.

• Why it matters: Understanding the evolution of HK97-fold protein shells addresses the paradox of their increasing complexity and the origins of viral capsids and biochemical compartments.
• What they did: Researchers searched environmental metagenomes for small genomes encoding HK97-fold proteins, using hidden Markov models and protein language models, and performed phylogenetic and structural analyses.
• The result: Findings support a bidirectional evolution model enabled by procapsids, proposing that HK97-fold shells originated as lower-symmetry compartments and may retain biochemical functions.