Data for: MHC I of the great reed warbler promotes a flat peptide binding mode

The major histocompatibility complex (MHC) plays a key role in pathogen
recognition as part of the adaptive immune system. MHC I gene copy numbers
in birds of the order Passeriformes (songbirds) are substantially larger
compared to other birds. MHC I diversity and antigen presentation have
been carefully characterized in chicken Gallus gallus of the order
Galliformes; chickens express few MHC I genes and often present antigens
that bulge out of the peptide binding cleft. This observation raises the
question whether MHC I present antigens in a similar way in species with
many MHC genes? Here, we present the X-ray structure of MHC I from the
great reed warbler Acrocephalus arundinaceus (Acar3) a long-distance
migratory songbird. Structural analysis shows that MHC I bind the antigen
in a flat conformation due to a sequentially well-conserved restriction
point, acting like a pair of tweezers, within the peptide binding grove,
created by Arg97 and Arg155. This more stringent antigen presentation by
Acar MHC I molecules may partly explain the high MHC gene copy numbers
seen in the great reed warbler.