NMR INVESTIGATION OF HUMAN CELL SURFACE RECEPTOR CD58: IMMUNOLOGY

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The goals of this research project are to determine the NMR solution structure of the adhesion domain of human cell surface receptor CD58, to study its interaction with the counter receptor CD2 and to develop a general strategy for producing a glycan-free form of glycoproteins without loss of function. The major result of this research project during 1998 is the successful NMR structural determination of a soluble mutant form of the CD58 adhesion domain, obtained through a structure-based rationalized design employing apolar-to-polar mutations of surface residues in functionally-irrelevant epitopes. The success of this structure-based approach was demonstrated through the E-coli expression of this functional 11 kDa adhesion domain extracted from the heavily glycosylated 55 kDa human CD58 ectodomain. The solution structure of the CD58 adhesion domain was subsequently determined using the NOESY. Other critical data were obtained from the Varian 750 MHz spectrometer at CMR, where we also studied via NMR the binding to its counter-receptor CD2. It has been shown that the CD58 adhesion domain adopts the immunoglobulin variable domain fold and consists of nine beta strands forming two parallel beta sheets. The new structural information supports a "hand-shake" model of CD2/CD58 interaction involving the GFCCU faces of both CD2 and CD58 adhesion domains. The region around the CC'Ioop of CD58 is most likely responsible for binding specificity while the negatively charged residues around the concave region near FG loop appear to contribute mainly to guiding the orientation during the docking of the two receptors. The structural information obtained thus far leads to promising experiments aimed at studying the solution structure of the complex formed between the two adhesion domains of CD58 and CD2. Due to the increased complexity of the CD2/CD58 binding complex structure, the experimental data from the 750 Nfflz spectrometer will have an even greater significance.