CRYSTAL STRUCTURE OF A CDR3 MUTANT OF A T CELL ANTIGEN RECEPTOR Va DOMAIN. Hongmin Li1, Marina I. Lebedeva1, E. Sally Ward2, and Roy A. Mariuzza1, 1Center for Advanced Research in Biotechnology, University of Maryland Biotechnology Institute, 9600 Gudelsky Drive, Rockville, MD 20850; 2University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75235-8576
The crystal structure of an engineered T cell receptor Va domain containing a grafted CDR3 was determined at 2.3Å resolution by molecular replacement using the wild type Va domain (1) as a search model. The final R factor is 0.156 with R.M.S. deviations from standard bond lengths and bond angles of 0.010Å and 1.936deg., respectively. Like the wild type Va, the mutant Va crystallized as a homodimer very similar to antibody VLVH dimers However, the relative orientation of the two chains in the mutant Va homodimer differs from that in the wild type by a rotation of 14deg.. The buried surface area in the dimer interface of the mutant is 24.1Å2 less than that in the wild type. While the residues forming the interface are essentially the same in the two structures, there are only five pairs of interface hydrogen bonds in the case of mutant compared with 17 for the wild type. This implies that the mutant Va homodimer is stabilized mainly by hydrophobic interactions. The difference in relative orientation of the Va domains in the two dimers will be discussed in the context of the variability in domain orientation reported for VLVL and VLVH dimers.
1. Fields et al, Science 270, 1821-1824 (1995).