Single-Jelly roll fold, horizontal
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.

Cellular homologs of the double jelly-roll major capsid proteins clarify the origins of an ancient virus kingdom
Mart Krupovic a, Kira S Makarova b, Eugene V Koonin b
Proc Natl Acad Sci U S A. 2022 Jan 25;119(5):e2120620119.
The logic of virus evolution
Eugene V Koonin, Valerian V Dolja, Mart Krupovic
Cell Host Microbe. 2022 Jul 13;30(7):917-929.
