The conserved His8 of the Moloney murine leukemia virus Env SU subunit directs the activity of the SU–TM disulphide bond isomerase

• Published in: Virology (New York, N.Y.) Vol. 361; no. 1; pp. 149 - 160
• Main Authors: Li, Kejun, Zhang, Shujing, Kronqvist, Malin, Ekström, Maria, Wallin, Michael, Garoff, Henrik
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 25.04.2007
• Subjects: Amino Acid Substitution; Animals; Cell Line; Cell Membrane - metabolism; CXXC-motif; Disulphide isomerization; Env activation; Fusion from without; Histidine - physiology; Hydrogen-Ion Concentration; Infectious Disease; Medicin och hälsovetenskap; Membrane Fusion; Moloney murine leukemia virus; Moloney murine leukemia virus - physiology; Murine leukemia virus; Protein Disulfide-Isomerases - metabolism; Protein Subunits - metabolism; Receptor binding; Receptors, Virus - metabolism; Structure-Activity Relationship; Thiol ionization; Viral Envelope Proteins - chemistry; Viral Envelope Proteins - metabolism; Virus Replication; Disulphide isomerization; Membrane fusion; Fusion from without; CXXC-motif; Receptor binding; Thiol ionization; Moloney murine leukemia virus; Env activation
• ISSN: 0042-6822; 1096-0341
• DOI: 10.1016/j.virol.2006.11.013

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.