Sandbox454: Difference between revisions
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== Structure and Function == | == Structure and Function == | ||
Pembrolizumab, or Keytruda, is an immunoglobulin G4 (IgG4)-kappa humanized monoclonal antibody against the programmed cell death-1 (PD-1) receptor. It is a very compact molecule with an asymmetrical Y-shape. The short compact hinge region inflicts constraints on the molecule that creates the abnormal crystallizable tail region (Fc domain) compared to other immunoglobulin G (IgG) proteins. The Fc domain is <scene name='74/745945/Glycosylation/1'>glycosylated</scene> at both CH2 domains on each chain and one of them is distinctively rotated 120° compared to other similar structures, making the glycan chain more solvent accessible and facing the solvent. IgG4s have a unique function where they form dynamic bispecific antibodies by exchanging half-molecules (one heavy chain/light chain pair) among themselves, called Fab-arm exchange. This makes the molecule particularly unstable and unpredictable as a treatment, but can be conquered by introducing a serine-to-proline mutation at <scene name='74/745945/Pro228/1'>amino acid 228</scene>, which prevents Fab-arm exchange and stabilizes the molecule <ref>DOI:10.1080/17425255.2016.1216976</ref>. | Pembrolizumab, or Keytruda, is an immunoglobulin G4 (IgG4)-kappa humanized monoclonal antibody against the programmed cell death-1 (PD-1) receptor. It is a very compact molecule with an asymmetrical Y-shape. The short compact hinge region inflicts constraints on the molecule that creates the abnormal crystallizable tail region (Fc domain) compared to other immunoglobulin G (IgG) proteins. The Fc domain is <scene name='74/745945/Glycosylation/1'>glycosylated</scene> at both CH2 domains on each chain and one of them is distinctively rotated 120° compared to other similar structures, making the glycan chain more solvent accessible and facing the solvent. IgG4s have a unique function where they form dynamic bispecific antibodies by exchanging half-molecules (one heavy chain/light chain pair) among themselves, called Fab-arm exchange. This makes the molecule particularly unstable and unpredictable as a treatment, but can be conquered by introducing a serine-to-proline mutation at <scene name='74/745945/Pro228/1'>amino acid 228</scene>, which prevents Fab-arm exchange and stabilizes the molecule <ref>DOI:10.1080/17425255.2016.1216976</ref>. Pembrolizumab contains an Fv fragment (PemFv) and a Fab fragment (PemFab). The Fv fragment is the variable region of the molecule where binding occurs whereas the Fab fragment constitutes the whole molecule. | ||
== Pembrolizumab/PD-1 Interaction == | == Pembrolizumab/PD-1 Interaction == | ||
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== PemFv/PD-1 Interaction == | == PemFv/PD-1 Interaction == | ||
The Fv fragment of pembrolizumab | The Fv fragment of pembrolizumab can form a complex with the extracellular domain (ECD) of PD-1. Both PemFv and PD-1ECD contain interchain disulfide bonds. PemFv interacts predominantly in the major groove of PD-1, which is formed on one surface by the CC’FG antiparallel β−sheet and the BC, C’D, and FG loops. There are 15 direct hydrogen bonds between the residues, 15 water-mediated hydrogen bonds, 2 salt bridges, and many hydrophobic interactions. A very large solvent-accessible surface area of 1,137Å2 is buried on PD-1ECD due to the convoluted interaction. There are a total of 26 PD-1ECD residues involved in the interaction with PemFv, with residues in loop C’D (Pro84 to Gly90) and strand C’ (Gln75 to Lys 78) playing a major role. These key components of PD-1 mainly form interactions through salt bridges and hydrogen bonds with CRD-L3, CDR-H1, CDR-H2, CDR-H3 of pembrolizumab. It is beleived that the sugar chains of PD-1 have no physical contact with pembrolizumab due to the N-linked glycosylated residues (Asn49, Asn58, Asn74, and Asn116) being located away from the interaface <ref name="horita" />. | ||
== PD-L1/PD-1 Interaction == | == PD-L1/PD-1 Interaction == | ||