The new antigen receptor (IgNAR) from sharks is a disul-phide bonded dimer of two protein chains,each containing one variable and five constant domains,and functions as an antibody. In order to assess the antigen-binding capabilities of isolated IgNAR variable domains (VNAR),we have con-structed anin vitro library incorporating synthetic CDR3 regions of 15–18 residues in length. Screening of this library against the 60 kDa cytosolic domain of the 70 kDa outer membrane translocase receptor from human mitochondria (Tom70) resulted in one dominant antigen-specific clone (VNAR12F-11) after four rounds ofin vitroselection
