The world is experiencing one of the most difficult moments in history with the COVID-19 pandemic, a disease caused by SARS-CoV-2, a new type of coronavirus. Virus infectivity is mediated by the binding of Spike transmembrane glycoprotein to specific protein receptors present on cell host surface. Spike is a homotrimer that emerges from the virion, each monomer containing two subunits named S1 and S2, which are related to cell recognition and membrane fusion, respectively. S1 is subdivided in domains S1A (or NTD) and S1B (or RBD), with experimental and in silico studies suggesting that the former binds to sialic acid-containing glycoproteins, such as CD147, whereas the latter binds to ACE2 receptor. Recent findings indicate that the ABO blood system modulates susceptibility and progression of infection, with type-A individuals being more susceptible to infection and/or manifestation of a severe condition. Seeking to understand the molecular mechanisms underlying this susceptibility, we carried out an extensive bibliographic survey on the subject. Based on this survey, we hypothesize that the correlation between the ABO blood system and susceptibility to SARS-CoV-2 infection can be presumably explained by the modulation of sialic acid-containing receptors distribution on host cell surface induced by ABO antigens through carbohydrate-carbohydrate interactions, which could maximize or minimize the virus Spike protein binding to the host cell. This model could explain previous sparse observations on the molecular mechanism of infection and can direct future research to better understand of COVID-19 pathophysiology.

The relation structure-activity of the Mimosoideae lectins of Parkia platycephala (PPL) and Parkia biglobosa (PBL) was analyzed in this study. PBL was solved by X-ray crystallography at a resolution of 2.1Å, and the crystal structure belonged to the C222 space group. Structural organization and binding sites were also characterized. Specifically, PBL monomer consists of three β-prism domains tandemly arranged with each one presenting a different carbohydrate recognition domain (CRD). PPL showed antinociceptive activity in the mouse model of acetic acid-induced writhes with maximal inhibitory effect by 74% at 1mg/mL. PPL also demonstrated anti-inflammatory effect causing inhibition of leukocyte migration induced by both direct and indirect chemoattractants. These PPL activities were compared to that of PBL described previously. Molecular docking of both PBL and PPL demonstrated some differences in carbohydrate-lectin interaction energy. Comparing structure and biological effects of the two lectins provided new data about their structure and the relation with its biological activities.

The three-dimensional structure of Dioclea reflexa seed lectin (DrfL) was studied in detail by a combination of X-ray crystallography, molecular docking and molecular dynamics. DrfL was purified by affinity chromatography using Sephadex G-50 matrix. Its primary structure was obtained by mass spectrometry, and crystals belonging to orthorhombic space group P222 were grown by the vapor diffusion method at 293K. The crystal structure was solved at 1.765Å and was very similar to that of other lectins from the same subtribe. The structure presented R and R of 21.69% and 24.89%, respectively, with no residues in nonallowed regions of Ramachandran plot. Similar to other Diocleinae lectins, DrfL was capable of relaxing aortic rings via NO induction, with CRD participation, albeit with low intensity (32%). In silico analysis results demonstrated that DrfL could strongly interact with complex N-glycans, components of blood vessel glycoconjugates. Despite the high similarity among Diocleinae lectins, it was also reported that each lectin has unique CRD properties that influence carbohydrate binding, resulting in different biological effects presented by these molecules.

A lectin from Canavalia virosa, Diocleinae subtribe, was purified by affinity chromatography with Sephadex G-50 matrix and named ConV. The primary structure of ConV was obtained by mass spectrometry and crystals were obtained by the vapor diffusion method at 293K and belonged to orthorhombic space group P222 with two molecules in its asymmetric unit. The structure obtained presented R and R of 18.91% and 24.92% respectively, with no residues in nonallowed regions of Ramachandran plot. The crystal structure was solved at 2.53Å and was demonstrated to be very similar to other lectins from the same subtribe. In inflammatory tests, ConV elicited paw edema, but incubation of lectin with glucose beforehand was able to reduce the edematogenic effect, indicating the involvement of the carbohydrate recognition domain in this process. The lectin also showed toxicity to rat C6 glioma cells, disrupting the mitochondrial membrane potential (ΔYm) and decreasing cell viability, indicating an anticancer potential for ConV. In silico studies confirmed that ConV interacts strongly with carbohydrates that comprise the N-glycans of glycoproteins. This finding corroborates the hypothesis which holds that the lectin domain interacts with glycans in molecular targets and that this contributes to the effects observed in biological activities.

Indole-3-acetic acid (IAA) bound is considered a storage molecule and is inactive. However, some studies have proposed an additional possible regulatory mechanism based on the ability of lectins to form complexes with IAA. We report the first crystal structure of ConM in complex with IAA at 2.15 Å resolution. Based on a tetrameric model of the complex, we hypothesize how the lectin controls the availability of IAA during the early seedling stages, indicating a possible new physiological role for these proteins. A free indole group is also bound to the protein. The ConM interaction with different forms of IAA is a strategy to render the phytohormone unavailable to the cell. Thus, this new physiological role proposed for legume lectins might be a novel mechanism by which IAA levels are decreased in addition to the destruction and formation of new complexes in the later stages of seed germination.