“The griffithsin dimer is required for high potency inhibition of HIV-1: Evidence for manipulation of the structure of gp120 as part of the griffithsin dimer mechanism”

Jie Xue, Bart Hoorelbeke, Ioannis Kagiampakis, Borries Demeler, Jan Balzarini, and Patricia J. LiWang Antimicrobial Agents and Chemotherapy 57:8, 3976–3989 (2013)

Griffithsin (Grft) is a protein lectin derived from red algae that tightly binds the HIV envelope protein gp120 and potently inhibits virus infection. This inhibition is due to the binding by Grft of high-mannose saccharides on the surface of gp120. Grft has been shown to be a tight dimer, but the role of the dimer in function has not been fully explored. To investigate the role of the Grft dimer in anti-HIV function, an obligate dimer of Grft was designed by expressing the protein with a peptide linker between the two subunits. This “Grft-linker-Grft” is a folded protein dimer, apparently nearly identical in structural properties with the wild-type protein. A “one-armed” obligate dimer was also designed, with each of the three carbohydrate binding sites of one subunit mutated while the other subunit remained intact. While both constructed dimers retained the ability to bind gp120 and the viral surface, Grft-linker-Grft-OneArm was 84- to 1010-fold less able to inhibit HIV compared to wild-type Grft, while Grft-linker-Grft had near wild-type antiviral potency. Furthermore, while the wild-type protein demonstrated the ability to alter the structure of gp120 by exposing the CD4 binding site, Grft-linker-Grft-OneArm largely lost this ability. In experiments to investigate gp120 shedding, it was found that Grft has different effects on gp120 shedding for strains from subtype B and subtype C, and this might correlate with Grft function. Evidence is provided that the dimer form of Grft is critical to the function of this protein in HIV inhibition.