7f5h | pdb_00007f5h
The crystal structure of RBD-Nanobody complex, DL28 (SC4)
Structural highlights
FunctionSPIKE_SARS2 attaches the virion to the cell membrane by interacting with host receptor, initiating the infection (By similarity). Binding to human ACE2 receptor and internalization of the virus into the endosomes of the host cell induces conformational changes in the Spike glycoprotein (PubMed:32142651, PubMed:32075877, PubMed:32155444). Uses also human TMPRSS2 for priming in human lung cells which is an essential step for viral entry (PubMed:32142651). Proteolysis by cathepsin CTSL may unmask the fusion peptide of S2 and activate membranes fusion within endosomes.[HAMAP-Rule:MF_04099][1] [2] [3] mediates fusion of the virion and cellular membranes by acting as a class I viral fusion protein. Under the current model, the protein has at least three conformational states: pre-fusion native state, pre-hairpin intermediate state, and post-fusion hairpin state. During viral and target cell membrane fusion, the coiled coil regions (heptad repeats) assume a trimer-of-hairpins structure, positioning the fusion peptide in close proximity to the C-terminal region of the ectodomain. The formation of this structure appears to drive apposition and subsequent fusion of viral and target cell membranes.[HAMAP-Rule:MF_04099] Acts as a viral fusion peptide which is unmasked following S2 cleavage occurring upon virus endocytosis.[HAMAP-Rule:MF_04099] Publication Abstract from PubMedSARS-CoV-2 and its variants, such as the Omicron continue to threaten public health. The virus recognizes the host cell by attaching its Spike (S) receptor-binding domain (RBD) to the host receptor, ACE2. Therefore, RBD is a primary target for neutralizing antibodies and vaccines. Here, we report the isolation and biological and structural characterization of a single-chain antibody (nanobody) from RBD-immunized alpaca. The nanobody, named DL28, binds to RBD tightly with a K (D) of 1.56 nM and neutralizes the original SARS-CoV-2 strain with an IC(50) of 0.41 mug mL(-1). Neutralization assays with a panel of variants of concern (VOCs) reveal its wide-spectrum activity with IC(50) values ranging from 0.35 to 1.66 mug mL(-1) for the Alpha/Beta/Gamma/Delta and an IC(50) of 0.66 mug mL(-1) for the currently prevalent Omicron. Competition binding assays show that DL28 blocks ACE2-binding. However, structural characterizations and mutagenesis suggest that unlike most antibodies, the blockage by DL28 does not involve direct competition or steric hindrance. Rather, DL28 may use a "conformation competition" mechanism where it excludes ACE2 by keeping an RBD loop in a conformation incompatible with ACE2-binding. Structural Characterization of a Neutralizing Nanobody With Broad Activity Against SARS-CoV-2 Variants.,Li T, Zhou B, Luo Z, Lai Y, Huang S, Zhou Y, Li Y, Gautam A, Bourgeau S, Wang S, Bao J, Tan J, Lavillette D, Li D Front Microbiol. 2022 Jun 2;13:875840. doi: 10.3389/fmicb.2022.875840. , eCollection 2022. PMID:35722331[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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