MATURATION INTERMEDIATES OF A T=4 VIRUS CAPSID STUDIED BY TIME-RESOLVED X-RAY SC

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Nudaurelia capensis omega virus-like particle, a T=4 virus capsid, undergoes a pH promoted maturation process. Using the much improved instrumentation on SSRL BL4-2 we have begun studying the kinetics of structural change associated with the maturation process. Prior to this effort, we detected a structural intermediate [Canady et al. J .Mol. Biol. 311, 803-814 (2001)], but the data quality achievable then did not permit us to analyze structural details. Very recent experiments demonstrate that a much smaller quantity of virus-like particle (VLP) is sufficient to obtain higher quality data due to the vastly improved instrumentation, in particular the improved detector sensitivity and larger 2D active area as well as the higher beam flux level. Performing manual mixing, followed by a series of time-resolved data acquisition (each 3 sec exposure), we have been able to isolate a structural intermediate at intermediary pH values between neutral (pH 7.6) and pH 5.0, which was used to promote the maturation in our earlier studies. The other important observation is that two VLPs with different RNA contents show slight different shape and diameter. This is the first direct experimental observation of the significant role of RNA scaffolding in virus morphology.