title: Solubilization and delivery by GroEL of megadalton complexes of the lambda holin.
abstract: GroEL can solubilize membrane proteins by binding them in its hydrophobic cavity when detergent is removed by dialysis. The best-studied example is bacteriorhodopsin, which can bind in the GroEL chaperonin at two molecules per tetradecamer. Applying this approach to the holin and antiholin proteins of phage lambda, we find that both proteins are solubilized by GroEL, in an ATP-sensitive mode, but to vastly different extents. The antiholin product, S107, saturates the chaperonin at six molecules per tetradecameric complex, whereas the holin, S105, which is missing the two N-terminal residues of S107, forms a hyper-solubilization complex with up to 350 holin molecules per GroEL, or approximately 4 MDa of protein per 0.8 MDa tetradecamer. Gel filtration chromatography and immunoprecipitation experiments confirmed the existence of complexes of the predicted masses for both S105 and S107 solubilization. For S105, negatively stained electron microscopic images show structures consistent with protein shells of the holin assembled around the chaperonin tetradecamer. Importantly, S105 can be delivered rapidly and efficiently to artificial liposomes from these complexes. In these delivery experiments, the holin exhibits efficient membrane-permeabilizing activity. The S107 antiholin can block formation of the hypersolubilization complexes, suggesting that their formation is related to an oligomerization step intrinsic to holin function.
authors.affiliation: Department of Biochemistry and Biophysics, Texas A and M University, 2128 TAMU, College Station, TX 77843-2128, USA.
authors.forename: John
authors.initials: J
authors.lastname: Deaton
authors.forename: Christos G
authors.initials: CG
authors.lastname: Savva
authors.forename: Jingchuan
authors.initials: J
authors.lastname: Sun
authors.forename: Andreas
authors.initials: A
authors.lastname: Holzenburg
authors.forename: Joel
authors.initials: J
authors.lastname: Berry
authors.forename: Ry
authors.initials: R
authors.lastname: Young
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry; D018835:Chaperonin 10 / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D018834:Chaperonin 60 / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D004926:Escherichia coli / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry; D008854:Microscopy, Electron; D046912:Multiprotein Complexes / Q000737:chemistry* / Q000648:ultrastructure; D011485:Protein Binding; D014764:Viral Proteins / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D018835:Chaperonin 10; D018834:Chaperonin 60; D008081:Liposomes; D046912:Multiprotein Complexes; D014764:Viral Proteins; C082001:bacteriophage lambda lysis effector protein S105; C082002:bacteriophage lambda lysis inhibitor protein S107; D000255:Adenosine Triphosphate