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Carmen Butan, Giovanni Cardone, Naiqian Cheng,

Bernard Heymann, Paul Keller, Dennis Winkler

Laboratory of Structural Biology, NIAMS-NIH

Parvez Lokhandwala, John Purdy, Rebecca Craven

Pennsylvania State University College of Medicine

* RSV Core Assembly: It’s All About Nucleation

Retroviruses are highly variable in their capsid architecture, both for a given retrovirus and between different retroviruses. With HIV, the predominant capsid morphology is biconical; with Rous sarcoma virus, it is irregular polyhedra. Cylindrical tubes with and without end-caps are also produced.

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Butan et al. (2008) J. Mol. Biol., 376, 1168-81

Cryo-electron tomogram of Rous sarcoma virus

Angular, curved and miscellaneous cores

Virions with angular cores have many spikes: Virions with tubular cores have few spikes

In retroviruses, the capsid assembles de novoinside the provirion, post-budding

Not all of the capsid protein assembles: > 50% remains unassembled (Prevelige et al; Fuller et al)

Angular cores correlate with high CA assembly efficiencies: Tubular cores correlate with low CA assembly efficiencies

Measure #Gag ( total # CA) from

virion diameter

Observations

- tubular cores and many “curved”cores - including biconical RSVcores - fail to package RNP

- The range of polymorphic variation is very large

- Hypothesis: a viable core is one that is closed and has successfully packaged the genome(s) and the polymerase

Observations

- tubular cores and many “curved”cores - including biconical RSVcores - fail to package RNP

- The range of polymorphic variation is very large

- Hypothesis: a viable core is one that is closed and has successfully packaged the genome(s) and the polymerase

- Inference: Initiation is key to capsid assembly

Critical concentrations for assembly

Total conc’n of protein subunits

conc

’n o

f pro

tein

sub

units

in c

apsi

ds

Nucleation of angular nucleocapsid assembly : a model