Hkb. Simmerman et al., A LEUCINE-ZIPPER STABILIZES THE PENTAMERIC MEMBRANE DOMAIN OF PHOSPHOLAMBAN AND FORMS A COILED-COIL PORE STRUCTURE, The Journal of biological chemistry, 271(10), 1996, pp. 5941-5946
Phospholamban is a phosphoprotein regulator of cardiac sarcoplasmic re
ticulum which is phosphorylated in response to beta-adrenergic stimula
tion. Previous results have shown that phospholamban forms Ca2+-select
ive channels in lipid bilayers. The channel-forming domain has been lo
calized to amino acid residues 26-52, which form a stable pentameric,
helical structure. The specific residues responsible for stabilizing t
he pentameric membrane domain of phospholamban have been identified by
mutational analysis. Residues 26-52 were individually mutated to Ala
or Phe, and the ability of the resulting mutant to form a pentamer or
other oligomer was assessed by SDS-polyacrylamide gel electrophoresis
analysis. Replacement of Leu(37), Ile(40), Leu(44), Ile(47), or Leu(51
) by Ala prevented pentamer formation, indicating their essential invo
lvement in the oligomeric assembly. The heptad repeats, and 3-4-residu
e spacing of the essential amino acids suggest that residues 37-52 ado
pt a pentameric coiled-coil structure stabilized by a leucine zipper m
otif formed by the close packing of Leu(37), Ile(40), Leu(44), Ile(47)
, and Leu(51). The resulting symmetric structure contains a central po
re defined by the hydrophobic surface of the five stabilizing leucine
zippers, which are oriented to the interior and form the backbone of t
he pentamer.