Nucleotide exchange and cGMP phosphodiesterase activation by pertussis toxin inactivated transducin

Biochemistry. 1991 Dec 17;30(50):11637-45. doi: 10.1021/bi00114a005.


Transducin, the signal coupling protein of retinal rod photoreceptor cells, is one of a family of G proteins that can be inactivated by pertussis toxin. We have investigated the nature of this inactivation in order to determine (1) whether it requires the toxin-catalyzed transfer of ADP-ribose from NAD+ to cysteine-347 of the alpha subunit and (2) whether it involves locking the alpha subunit in the inactive conformation characteristic of its GDP-bound state, or is limited to disruption of binding to photoexcited rhodopsin (R*). Our results indicate that all observed effects of pertussis toxin treatment, including a shift in the electrophoretic mobility of transducin's alpha subunit and functional inactivation, require NAD+ and that the appearance of the shift parallels incorporation of ADP-ribose. We have also found that, apart from interactions with photoexcited rhodopsin, the functional properties of ADP-ribosylated transducin are essentially the same as those of unmodified transducin. Normal spontaneous nucleotide exchange kinetics and the ability to activate cGMP phosphodiesterase are preserved following quantitative ADP-ribosylation, as are the abilities to hydrolyze GTP, to bind to a dye affinity column, and to display enhanced fluorescence upon addition of Al3+ and F-. Thus, ADP-ribosylation merely blocks catalysis of transducin nucleotide exchange by R* and does not lock transducin in an inactive state.(ABSTRACT TRUNCATED AT 250 WORDS)

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 3',5'-Cyclic-GMP Phosphodiesterases / metabolism*
  • Adenosine Diphosphate Ribose / metabolism
  • Animals
  • Catalysis
  • Cattle
  • Electrophoresis, Polyacrylamide Gel
  • Enzyme Activation
  • Hydrolysis
  • Kinetics
  • NAD / metabolism
  • Nucleotides / metabolism*
  • Pertussis Toxin*
  • Rod Cell Outer Segment / metabolism
  • Structure-Activity Relationship
  • Transducin / antagonists & inhibitors*
  • Transducin / metabolism
  • Tryptophan
  • Virulence Factors, Bordetella / pharmacology*


  • Nucleotides
  • Virulence Factors, Bordetella
  • NAD
  • Adenosine Diphosphate Ribose
  • Tryptophan
  • Pertussis Toxin
  • 3',5'-Cyclic-GMP Phosphodiesterases
  • Transducin