title: The conserved His8 of the Moloney murine leukemia virus Env SU subunit directs the activity of the SU-TM disulphide bond isomerase.
abstract: Murine leukemia virus (MLV) fusion is controlled by isomerization of the disulphide bond between the receptor-binding surface (SU) and fusion-active transmembrane subunits of the Env-complex. The bond is in SU linked to a CXXC motif. This carries a free thiol that upon receptor binding can be activated (ionized) to attack the disulphide and rearrange it into a disulphide isomer within the motif. To find out whether His8 in the conserved SPHQ sequence of Env directs thiol activation, we analyzed its ionization in MLV vectors with wtEnv and Env with His8 deleted or substituted for Tyr or Arg, which partially or completely arrests fusion. The ionization was monitored by following the pH effect on isomerization in vitro by Ca2+ depletion or in vivo by receptor binding. We found that wtEnv isomerized optimally at slightly basic pH whereas the partially active mutant required higher and the inactive mutants still higher pH. This suggests that His8 directs the ionization of the CXXC thiol.
authors.affiliation: Department of Biosciences and Nutrition, Karolinska Institute, S-141 57 HUDDINGE, Sweden.
authors.forename: Kejun
authors.initials: K
authors.lastname: Li
authors.forename: Shujing
authors.initials: S
authors.lastname: Zhang
authors.forename: Malin
authors.initials: M
authors.lastname: Kronqvist
authors.forename: Maria
authors.initials: M
authors.lastname: Ekström
authors.forename: Michael
authors.initials: M
authors.lastname: Wallin
authors.forename: Henrik
authors.initials: H
authors.lastname: Garoff
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D006639:Histidine / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D008561:Membrane Fusion; D008979:Moloney murine leukemia virus / Q000502:physiology*; D019704:Protein Disulfide-Isomerases / Q000378:metabolism*; D021122:Protein Subunits / Q000378:metabolism; D011991:Receptors, Virus / Q000378:metabolism; D013329:Structure-Activity Relationship; D014759:Viral Envelope Proteins / Q000737:chemistry / Q000378:metabolism*; D014779:Virus Replication
chemical_list: D021122:Protein Subunits; D011991:Receptors, Virus; D014759:Viral Envelope Proteins; D006639:Histidine; D019704:Protein Disulfide-Isomerases