TI  - Mutagenesis of the regulatory subunit (<prot>RII beta</prot>) of <prot>cAMP-dependent protein
      kinase II beta</prot> reveals hydrophobic amino acids that are essential for <prot>RII
      beta</prot> dimerization and/or anchoring <prot>RII beta</prot> to the cytoskeleton.
PG  - 1935-44
AB  - In neurons <prot>cAMP-dependent  protein kinase II beta</prot> (<prot>PKAII beta</prot>)  is
      sequestered in the dendritic cytoskeleton because the regulatory subunit
      (<prot>RII beta</prot>) of the enzyme is tightly bound by  A Kinase Anchor Proteins
      (AKAPs) . The prototypic neuronal anchor protein <prot>AKAP75</prot> has a COOH-terminal
      22-residue <prot>RII beta</prot> binding (tethering) site. A key feature of the
      tethering site is that several amino acids with large aliphatic side
      chains mediate the high-affinity binding of <prot>RII beta</prot>. Mutagenesis,
      recombinant protein expression, and physicochemical characterization were
      used to investigate the structural basis for the homodimerization and
       <prot>AKAP75</prot>  binding activities of    <prot>RII beta</prot>   . Several crucial residues are
      located in an NH2-terminal region that encompasses amino acids 13-36.
      Substitution of Ala for Leu13 or Phe36 generates monomeric <prot>RII beta</prot>
      subunits that cannot bind <prot>AKAP75</prot>. The results are not due to general
      misfolding since mutant  <prot>RII beta</prot>  monomers bind  cAMP  and inhibit the
      catalytic subunit of <prot>PKAII beta</prot> with the same affinity and efficacy as
      wild-type <prot>RII beta</prot> dimers. Moreover, substitution of Ala for Leu12, Val20,
      Leu21, Phe31, Leu33, or Leu39 and replacement of Leu13 with Ile or Val did
      not impair the dimerization reaction. Evidently, large hydrophobic side
      chains of Leu13 and Phe36 play pivotal roles in stabilizing  <prot>RII beta</prot> - <prot>RII
      beta</prot>  interactions. A secondary consequence of destabilizing <prot>RII beta</prot>
      dimers is the loss of intracellular targeting/anchoring capacity because
      monomers fail to bind <prot>AKAP75</prot>. Other NH2-terminal residues directly
      modulate the affinity of <prot>RII beta</prot> dimers for the <prot>AKAP75</prot> tethering site.
      Replacement of Val20-Leu21 with Ala-Ala produced a dimeric    <prot>RII beta</prot>   
      protein that binds  <prot>AKAP75</prot>  approximately 4% as avidly as wild-type <prot>RII
      beta</prot>. It is possible that the aliphatic side chains of Val20 and Leu21
      interact with the essential Leu and Ile residues in the <prot>AKAP75</prot> tethering
      region.
AD  - Department of Molecular Pharmacology, Atran Laboratories, Albert Einstein
