PMID: 27411955

Authors:

Alam A, Woo JS, Schmitz J, Prinz B, Root K, Chen F, Bloch JS, Zenobi R, Locher KP

Title:

Structural basis of transcobalamin recognition by human CD320 receptor.

Journal:

Nat Commun. 2016 Jul 14;7:12100. doi: 10.1038/ncomms12100.

Abstract:

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 CD320DeltaE88 mutant and for the isolated LDLR-A2 domain. We also determined the structure of the TC-CD320DeltaE88 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.