RetroCA-fold

RetroCA-fold proteins form icosahedral capsids characteristic of reverse-transcribing viruses. These proteins are structurally flexible and can assemble into hexamers or pentamers, thereby generating capsids of diverse shapes and sizes .

Capsids from Spumavirinae and some Orthoretrovirinae assemble with T=13 symmetry, whereas Alpharetroviruses form T=1 symmetry capsids.

Origin

The N-terminal domain is unique to reverse-transcribing viruses, while the C-terminal domain is homologous to the SCAN domain (PF02023), a protein?interaction module found in vertebrate transcription factors. The evolutionary origin of this domain remains unclear .

Topology

The fold comprises two domains:

• An N-terminal domain of seven alpha-helices, which assembles into pentamers or hexamers.
• A C-terminal domain of four alpha-helices, which mediates interactions between CA multimers to form the complete capsid.

HIV-1 CA 3DIK