Domain-Swapped Structure of the Potent Antiviral Protein Griffithsin and Its Mode of Carbohydrate Binding

Abstract

The crystal structure of griffithsin, an antiviral lectin from the red alga Griffithsia sp., was solved and refined at 1.3 A resolution for the free protein and 0.94 A for a complex with mannose. Griffithsin molecules form a domain-swapped dimer, in which two beta strands of one molecule complete a beta prism consisting of three four-stranded sheets, with an approximate 3-fold axis, of another molecule. The structure of each monomer bears close resemblance to jacalin-related lectins, but its dimeric structure is unique. The structures of complexes of griffithsin with mannose and N-acetylglucosamine defined the locations of three almost identical carbohydrate binding sites on each monomer. We have also shown that griffithsin is a potent inhibitor of the coronavirus responsible for severe acute respiratory syndrome (SARS). Antiviral potency of griffithsin is likely due to the presence of multiple, similar sugar binding sites that provide redundant attachment points for complex carbohydrate molecules present on viral envelopes.

Novel Fold and Carbohydrate Specificity of the Potent Anti-HIV Cyanobacterial Lectin from Oscillatoria agardhii

“…Titration data sets were recorded for 15 Nlabeled OAA at 0.020 mM, and spectra in the absence and presence of ϳ0.016 mM Man-9 (OAA/Man-9 molar ratio of 1:0.8) and ϳ0.048 mM Man-9 (OAA/Man-9 molar ratio of 1:2.4) are provided in Fig. 5.…”

“…Carbohydrate Binding Studies by NMR Spectroscopy-Binding of Man-9 (V-Labs) was investigated at 25°C using 0.020 mM 15 15 N HSQC spectroscopy at 600 MHz. Because Man-9 is not readily available and very expensive, spectra were recorded for only two titration points at protein/Man-9 molar ratios of 1:0.8 and 1:2.4 (molar ratios of 1:0.4 and 1:1.2 for an individual binding site for sugar).…”

“…Interestingly, the binding modes and target epitopes on Man-9 are quite distinct for the different lectins. Cyanovirin-N specifically recognizes Man␣(1-2)Man-linked mannose substructures, in particular the D1 and D3 arms of Man-9 (12, 13); DC-SIGN preferentially interacts with the Man␣(1-3)Man␣(1-6)Man trisaccharide (14); griffithsin binds to single mannose units (15); and MVL specifically interacts with the Man␣(1-6)Man␤(1-4)GlcNAc␤(1-4)GlcNAc tetrasaccharide (16). Although no crystal structures for protein-carbohydrate complexes are available for scytovirin and actinohivin, sugar binding studies revealed specificities for Man␣(1-2)Man␣(1-6)Man␣(1-6)Man (17) and Man␣(1-2)Man (18), respectively.…”

Binding of the Mannose-Specific Lectin, Griffithsin, to HIV-1 gp120 Exposes the CD4-Binding Site

“…(41). GRFT exists exclusively as a dimer and has a domain-swapped structure in which two ␤-strands of one monomer combine with 10 ␤-strands of the other monomer to form a ␤ prism of three four-stranded sheets (63,64). Each GRFT monomer contains three binding sites that have high affinity for mannose residues.…”

Griffithsin-Modified Electrospun Fibers as a Delivery Scaffold To Prevent HIV Infection

“…Moreover, to the benefit of intravaginal administration, GRFT lacks the capacity to induce proinflammatory cytokines in human peripheral blood mononuclear cells, is resistant to a broad array of human proteases, and is stable in the presence of culture medium from vaginal microbes, retaining anti-HIV activity for up to 10 days, even when some of the six carbohydrate binding sites are occupied (55,56). Mechanistically, GRFT has been shown to bind the terminal mannose N-linked glycan residues on viral envelope surfaces (51,55,(57)(58)(59). For HIV-1, GRFT is believed to bind to gp120 on the virion and neutralize the virus at entry, whereas for HSV-2, GRFT inhibits infection via the glycoprotein (gP) conformational changes expressed during cell-to-cell spread (46).…”