PMID: 12122212

 

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Title : The crystal structure of human CD21 : Implications for Epstein-Barr virus and C3d binding

Abstract :

1. Human complement receptor type 2 2 (CD21 ) is the cellular receptor for Epstein-Barr virus (EBV) , a human tumor virus
2. The N-terminal two short consensus repeats (SCR1- SCR2 ) of the receptor interact with the EBV glycoprotein gp350/220 and also with the natural CD21 ligand C3d
3. Here we present the crystal structure of the CD21 SCR1- SCR2 fragment in the absence of ligand and demonstrate that it is able to bind EBV
4. Based on a functional analysis of wild-type and mutant CD21 and molecular modeling, we identify a likely region for EBV attachment and demonstrate that this region is not involved in the interaction with C3d
5. A comparison with the previously determined structure of CD21 SCR1- SCR2 in complex with C3d shows that, in both cases, CD21 assumes compact V-shaped conformations
6. However, our analysis reveals a surprising degree of flexibility at the SCR1- SCR2 interface, suggesting interactions between the two domains are not specific
7. We present evidence that the V-shaped conformation is induced by deglycosylation of the protein , and that physiologic glycosylation of CD21 would result in a more extended conformation, perhaps with additional epitopes for C3d binding