This domain, named as the SECRET domain, is found at the C-terminal end of Tumour necrosis factor receptor (CrmD) from the orthopoxvirus Ectromelia virus. This domain binds a subset of human and mouse CC, CXC and C chemokines. It is thought to be responsible for the anti-chemokine activity of CrmD. The SECRET domain monomer adopts a beta-sandwich fold, consisting of two parallel beta-sheets with five and six anti-parallel strands, and the connecting loops [1]. This domain is also found in other uncharacterised sequences from poxvirus, including Protein OPG192 and Protein C8 from Vaccinia virus.

1: Structural basis of chemokine sequestration by CrmD, a poxvirus-encoded tumor necrosis factor receptor. Xue X, Lu Q, Wei H, Wang D, Chen D, He G, Huang L, Wang H, Wang X; PLoS Pathog. 2011;7:e1002162. PMID:21829356