Single-Jelly roll fold, horizontal

The single jelly-roll fold is composed of eight β-strands arranged in two four-stranded sheets. This architecture forms the capsid shells with T=1, T=3, T=4, or T=7 symmetry.

The fold also occurs in non-capsid proteins, such as minor capsid proteins, polyhedrin (found in occlusion bodies), and in several viral glycoproteins, including influenza hemagglutinin (1RU7) and coronavirus spikes (6VYB).

Origin:

There appear to be four main structural groups, which might reflect four different cellular origins :

• The Riboviria and Monodnaviria group (T=1, T=3) may have evolved from cellular lectins, like Cel9A.
• The Microviridae and Bromoviridae group (T=1, T=3) might have come from TNF superfamily proteins.
• The Papovaviricetes group (Polyomaviridae +Papillomaviridae) (T=7) has an unknown origin.
• The Singelaviria group (T=28) may have evolved from cupin-like proteins.

Topology

By convention, the β-strands are designated B through I, a nomenclature that traces back to the first jelly-roll structure solved-the Tomato bushy stunt virus capsid protein-which included an extra strand A positioned outside the conserved core. The fold comprises two ?-sheets formed by strands BIDG and CHEF, oriented so that strand B faces C, I faces H, and so on.