Cryo-electron tomography of trimeric SIV and HIV-1 envelope glycoproteins: computational separation of conformational heterogeneity in mixed populations

Wednesday, October 26, 2011 — Poster Session IV
2:00 p.m. – 4:00 p.m.	Natcher Conference Center	NCI	VIROL/MICRO-7

Authors

• GA Frank
• A Bartesaghi
• O Kuybeda
• MJ Borgnia
• TA White
• G Sapiro
• S Subramaniam

Abstract

Recent advances in cryo-electron tomography combined with 3D image averaging and classification have allowed determination of distinct “closed” and “open” conformations of trimeric envelope glycoprotein spikes (Env) as displayed on the surface of intact simian and human immunodeficiency viruses (SIV and HIV, respectively). The averaging approaches that have been used so far to obtain structures have relied on specimens where there is a single dominant species of trimeric Env in unliganded or liganded states present in the virus preparations. However, since native SIV and HIV-1 virus preparations can contain more than one sequence variant of Env, it is important to be able to distinguish the presence of multiple conformational states of Env in mixed viral populations. Using automated, iterative, missing wedge-corrected 3D image alignment and classification methods, we have developed computational procedures that allow clear separation of the closed and open states, as well as unliganded and antibody liganded states of trimeric Env when they are present in mixtures. We show that identifying and removing spikes with the lowest signal-to-noise ratios improves the overall accuracy of alignment between individual spikes, and that alignment accuracy, in turn, determines the success of image classification in assessing conformational heterogeneity of Env.

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