In vivo homodimerisation of HTLV-1 Gag and MA gives clues to the retroviral capsid and TM envelope protein arrangement.
During retroviral particle formation, the capsid precursors (Gag) associate with the cell membrane via their matrix (MA) domain to form viral assembling particles. After budding, Gag and its proteolytically matured MA, form a shell in the released immature and mature particles, respectively. Although the arrangement of Gag domains in vitro and their radial organisation in retroviral particles have been extensively studied, little is known concerning Gag inter-subunit interactions in authentic retroviruses. We report that human T-cell leukemia virus type 1 Gag homodimerises in the cell via a disulphide bonding at cysteine 61 in the MA domain. Most Gags are homodimeric after budding and MAs are also dimeric in mature authentic virions. Molecular modelling of the MA domain indicates that non-covalent interactions at the MA dimer interface may also be important for Gag (and MA) dimerisation. In addition, all amino acids previously reported to be involved in MA-transmembrane (TM) interactions are located on the MA face opposite to the dimer interface. The model reveals that homodimerisation is compatible with a hexameric network of Gag and MA dimers that look like the hexameric networks observed for other retroviruses. These data, together with previous studies, lead us to propose a supra-molecular arrangement model in which the transmembrane glycoproteins of the virion envelope are anchored in a hexameric cage hole formed by the MA.
INSERM U443, Equipe Rétrovirus et Transfert génique, 146, rue Léo Saignat, F-33076 Bordeaux Cedex, France.
Fabienne
F
Rayne
Andrey V
AV
Kajava
Jacqueline
J
Lalanne
Robert Z
RZ
Mamoun
D000595:Amino Acid Sequence; D036022:Capsid Proteins / Q000378:metabolism*; D003553:Cystine / Q000378:metabolism; D019281:Dimerization; D015683:Gene Products, gag / Q000378:metabolism*; D015368:Human T-lymphotropic virus 1 / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D014759:Viral Envelope Proteins / Q000378:metabolism*; D014763:Viral Matrix Proteins / Q000378:metabolism*
D036022:Capsid Proteins; D015683:Gene Products, gag; D014759:Viral Envelope Proteins; D014763:Viral Matrix Proteins; D003553:Cystine