STRUCTURE OF THE MENGO VIRION .6. SPATIAL RELATIONSHIPS OF THE CAPSID POLYPEPTIDES AS DETERMINED BY CHEMICAL CROSS-LINKING ANALYSES

The asymmetric structure unit of the Mengo virus capsid comprises one molecule each of the polypeptides α, β, and γ. Structure units are clustered in pentamers which are centered at each of the 12 vertices of a T = 1 icosahedral lattice (Mak et al., 1974). The location of the ∼-60 δ polypeptides in the capsid has not been established. In order to obtain information about the arrangement of α, β, and γ in the structure unit and to determine which polypeptides participate in the noncovalent interactions responsible for pentamer formation and capsid stabilization, virions were reacted with bifunctional crosslinking reagents and the polypeptide complexes produced were identified by gel electrophoresis. Using the reversible crosslinkers dimethylsuberimidate (DMS) and dithiobis(succinimidyl propionate) (DSP), positive identification of βγ, αγ, αβγ, α2, α3, and α4 complexes was made. Complexes involving S were not detected, nor were βn or γn. The latter observation indicated that the hydrophobic interactions among αβψ structure units in a pentamer involve α-α contacts. When virions crosslinked with DMS, DSP, or dimethyladipimate (DMA) were subsequently dissociated by 0.1 M NaCl at pH 6 and examined in the electron microscope, it was shown that only treatment with DSP prevented complete capsid dissociation. Since DSP crosslinking alone produced αβ complexes, it was concluded that the interactions between adjacent pentamers probably result from α-β contacts. Treatment of Mengo virions with formaldehyde produced crosslinks between β and γ polypeptides and the RNA. Based upon these data, a model for the organization of individual polypeptide species within the Mengo virus capsid is presented. © 1979.