title: Extracellular portions of HLA antigens are not compact globulae.
abstract: Membranes of human spleen cells were hydrolyzed by papain and the extracellular portions of HLA antigen molecules isolated by monoclonal antibodies fixed on Sepharose. The isolated proteins were spin-labeled by TEMPO-dichlorotriazine. The values of rotational correlation times (tau) of spin-labeled proteins were calculated using dependencies of magnetic parameters found from ESR spectra vs viscosity at constant temperature. The tau-values were equal to 8 nsec for class I molecules and 14 nsec for class II molecules. These values were significantly lower than those predicted for a rigid sphere with dimensions equal to the extracellular portions of HLA molecules (20 nsec). This fact suggests the existence of flexibility in poly-functional HLA molecules, which seems to be important for their biological activity. In this respect, extracellular portions of HLA molecules resemble flexible Fc fragments (tau = 12 nsec) and differ from rigid Fab fragments (tau = 20 nsec) of immunoglobulins G. The rotation of the oligosaccharide chains attached to HLA molecules is restricted.
authors.affiliation: Institute of Molecular Biology, USSR Academy of Sciences, Moscow.
authors.forename: R S
authors.initials: RS
authors.lastname: Nezlin
authors.forename: E V
authors.initials: EV
authors.lastname: Pankratova
authors.forename: A E
authors.initials: AE
authors.lastname: Arutyunyan
authors.forename: V P
authors.initials: VP
authors.lastname: Timofeev
mesh_terms: D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002847:Chromatography, Agarose; D004578:Electron Spin Resonance Spectroscopy; D006680:HLA Antigens; D006681:HLA-D Antigens; D006801:Humans; D013154:Spleen / Q000276:immunology
chemical_list: D006680:HLA Antigens; D006681:HLA-D Antigens