Fig. 1: Overview of the novel fold adopted by the SFV RBD.

a Schematic representation of SFV Env protein organization indicating the three constituent chains: leader peptide (LP), surface subunit (SU), and transmembrane subunit (TM). The transmembrane domains anchoring the LP and TM in the membrane are represented as black boxes; the receptor-binding domain (RBD) within SU is highlighted in blue-red spectrum; the fusion peptide at the N-terminus of the TM is shown in blue. The furin sites between the LP and SU (RIAR¹²⁶), and SU and TM (RRKR⁵⁷⁰) are indicated with scissors icons. The RBD expression construct contained the exogenous BiP signal at the N-terminus, residues 218 to 552 of the SFV gorilla GII Env and a double strep tag at the C-terminus (shown as two circles). The region comprising residues 420–426 is drawn as a dashed line because it was not seen in the electron density map. The 17 putative N-glycosylation sites for gorilla SFV Env are indicated with star symbols and labeled N1 to N15, following the previously established nomenclature²². b The X-ray structure of the RBD^D is shown in ribbon model colored from N- to C-terminus in blue to red spectrum, respectively. The dashed-line indicates the separation between the upper and lower subdomains. The N-glycosylation sites are indicated with N, and the sugars and the asparagine side chains carrying them are displayed as sticks. The figure was created with Pymol⁶⁵. c Linear representation of the RBD. The 8 N-glycosylation sites with sugars built into the electron density are shown as gray stars, including site N10 (N411) that showed density for an attached carbohydrate in RBD^G (molecule B), but not in RBD^D. Site N8 (N390), which contains a long, partially buried sugar moiety is highlighted with a thicker outline. The locations of six disulfides are indicated with numbered yellow circles as in panel b. The figure was created in BioRender.com.