CRYSTAL-STRUCTURE OF A CAMEL SINGLE-DOMAIN V-H ANTIBODY FRAGMENT IN COMPLEX WITH LYSOZYME

The Camelidae is the only taxonomic family known to possess functional heavy-chain antibodies, lacking light chains. We report here the 2.5 Angstrom resolution crystal structure of a camel V-H in complex with i ts antigen, lysozyme. Compared to human and mouse V-H domains, there a re no major backbone rearrangements in the V-H framework. However, the architecture of the region of V-H that interacts with a V-L in a conv entional Fv is different from any previously seen. Moreover, the CDR1 region, although in sequence homologous to human CDR1, deviates fundam entally from the canonical structure. Additionally, one half of the CD R3 contacts the V-H region which in conventional immunoglobulins inter acts with a V-L, whereas the other half protrudes from the antigen bin ding site and penetrates deeply into the active site of lysozyme.