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Alam, A, Woo, JS, Schmitz, J, Prinz, B, Root, K, Chen, F, Bloch, JS, Zenobi, R and Locher, KP (2016) Structural basis of transcobalamin recognition by human CD320 receptor. Nat Commun 7:12100


Cellular uptake of vitamin B12 (cobalamin) requires capture of transcobalamin (TC) from the plasma by CD320, a ubiquitous cell surface receptor of the LDLR family. Here we present the crystal structure of human holo-TC in complex with the extracellular domain of CD320, visualizing the structural basis of the TC-CD320 interaction. The observed interaction chemistry can rationalize the high affinity of CD320 for TC and lack of haptocorrin binding. The in vitro affinity and complex stability of TC-CD320 were quantitated using a solid-phase binding assay and thermostability analysis. Stable complexes with TC were also observed for the disease-causing CD320ΔE88 mutant and for the isolated LDLR-A2 domain. We also determined the structure of the TC-CD320ΔE88 complex, which revealed only minor changes compared with the wild-type complex. Finally, we demonstrate significantly reduced in vitro affinity of TC for CD320 at low pH, recapitulating the proposed ligand release during the endocytic pathway.


PubMed PMC4947154 Online version:10.1038/ncomms12100


Antigens, CD/chemistry; Antigens, CD/metabolism; Crystallography, X-Ray; Histidine/metabolism; Humans; Hydrogen-Ion Concentration; Models, Molecular; Protein Domains; Structure-Activity Relationship; Transcobalamins/chemistry; Transcobalamins/metabolism