Mechanism of action of monoclonal antibodies that block the light activation of the guanyl nucleotide-binding protein, transducin.

作者：Heidi E. Hamm, Dusanka Deretic, Kay Hofmann, Andreas Schleicher, Bernd Kohl · 发表于：Journal of Biological Chemistry · 年份：1987 · DOI：10.1016/s0021-9258(18)61039-7 · 被引用次数：69 · 研究领域：Receptor Mechanisms and Signaling、Retinal Development and Disorders、bioluminescence and chemiluminescence research

Seven monoclonal antibodies to the alpha subunit (G alpha) of the frog photoreceptor guanyl nucleotide-binding protein (transducin or G-protein) have been characterized as to their effect on G-protein function, and this has been correlated in the accompanying paper (Deretic, D., and Hamm, H. E. (1987) J. Biol. Chem. 262, 10839-10847) with the antibody-binding sites on G alpha tryptic fragments. Antibodies 4A, 7A, 7B, 7C, and 7D are members of a class of antibodies that block G-protein activation by light and therefore also block activation of the cGMP phosphodiesterase. All these blocking antibodies also block the interaction of G-protein with rhodopsin as measured by the light-scattering "binding signal," and as measured by the stabilization of meta-rhodopsin II by bound G-protein (extra-meta-rhodopsin II). The antibodies (or Fab fragments) also solubilize G alpha beta gamma from the membrane in the dark under isosmotic conditions and thus interfere with G alpha interaction with the membrane. Antibody 4A also blocks the extra-meta-rhodopsin II generated by G-protein-rhodopsin interaction in detergent solubilized membranes. Thus, even in the absence of phospholipids, antibody 4A blocks G-protein-rhodopsin interaction. Therefore, we suggest that the antibodies recognize a region of G alpha involved with binding to rhodopsin. An alternative hypothesis is that this antigenic site is a region of interaction between the alpha and beta gamma subunits, disruption of this interaction...