The Activation of Transducin: Studies on its Mechanism and Modulation

Hofmann, Klaus; Kahlert, M.

doi:10.1007/978-3-642-76482-0_7

Cited by 1 publication

(1 citation statement)

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“…In a more detailed study on mutants displaying this phenotype, it could be shown that a mutant lacking 13 amino acids of loop EF bound G I and formed an R* -G, oGDP-complex which was severely impaired in release of GDP. 102 This has shown that, by contrast to previous assumptions, 115 such mutants do not even operate the MIIIGDP switch (Fig. 2).…”

Section: Complexity Of the Interaction Domainscontrasting

confidence: 49%

Structure and Function of Activated Rhodopsin

Hofmann

Jäger

Ernst

1995

Israel Journal of Chemistry

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Abstract. After cis/trans isomerization of retinal and early photoproducts, activated rhodopsin (R*) develops signaling states for different proteins in a time-ordered sequence. Rhodopsin kinase binds all Meta forms, including the early Meta I, while interaction with transducin (G,) or arrestin requires the deprotonated Schiff base form, Meta II (MIl). G, recognizes a specific conformation, termed MIl b , which arises from an additional, spectrally silent conversion, linked to proton uptake. Collisional coupling with the GDP-bound G, holoprotein induces the release of GDP and formation of a stable R*-G, complex, in which the nucleotide binding site of G, is empty. The empty site complex, once formed, remains stable, even if the retinal is re-isomerized to the cis configuration. The cytoplasmic surface of rhodopsin appears to provide the majority of interaction sites for other proteins. Physical analyses and mutagenesis have emphasized the loops connecting helices CID and ElF of the seven-helix structure. Any interaction between R* and G, depends on a conserved charge pair at the interface between the helix C and the adjacent loop CD. Replacements or deletions in loops CD and EF were found to cause more specific functional defects, including slow release of GDP or failure of GTP-induced complex dissociation. In the dark, signaling states with low activity can be generated by reversible binding of all-trans-retinal to opsin. These lightindependent signaling states are different from the Meta forms.

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Section: Complexity Of the Interaction Domainscontrasting

confidence: 49%