Sandbox454: Difference between revisions

== Pembrolizumab/PD-1 Interaction ==

In order for pembrolizumab to block PD-1, pembrolizumab forms a large, flat paratope (antigen-binding site) that can sustain PD-1’s large epitope (where antibody attaches on antigen). The induced interaction between pembrolizumab and PD-1 gives rise to a surface conformational change on PD-1. The new structure of PD-1 becomes a very shallow, “crescent”-like shape, in contrast to it’s flat conformation when bound to PD-L1 <ref>DOI: 10.1038/srep35297<ref/>.  

== PemFv/PD-1 Interaction ==

The Fv fragment of pembrolizumab (PemFv) 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 phsyical contact with pembrolizumab due to the N-linked glycosylated residues (Asn49, Asn58, Asn74, and Asn116) being located away from the interaface <ref>DOI: 10.1038/srep35297<ref/>.   

== PD-L1/PD-1 Interaction ==

The complex formed when protein-derived ligand, PD-L1, interacts with the inhibitory receptor, PD-1, suppresses immune responses again autoantigens and helps in peripheral immune tolerance. However, when tumors overexpress PD-L1, the interaction with PD-1 inhibits T-lymphocyte proliferation, release of cytokines, and cytotoxicity, exhausting tumor-specific T-cells. There are a total of 12 PD-1ECD residues that are involved in forming the complex with the N-terminal half of PD-L1ECD (PD-L1ECD-N). Nine hydrogen bonds, 3 water-mediated hydrogen bonds, 2 salt bridges, and numerous hydrophobic interactions make up the PD-1ECD/PD-L1ECD-N interaction.The CC’FG sheet within both proteins is the main interaction point. A hydrophobic surface patch is formed when the PD-1ECD is in complex with PD-L1ECD-N. The PD-1ECD residues involved include Val64, Tyr68, Ile126, Leu128, Ala132 and Ile134. Numerous hydrophilic amino acids that encircle PD-L1ECD-N form salt bridges and hydrogen bonds with Asn66, Tyr68, Gln75, Thr76, Asp77, Lys78, Ala132 and Glu136 of PD-1ECD <ref>DOI: 10.1038/srep35297<ref/>.