Investigators

Summary

I study the structure and function of macromolecular complexes, such as virus capsids, using cryo-electron microscopy (cryoEM) to detail protein folds and interfaces. The resolution achieved by cryoEM depends on the sample, and we routinely aim for 3-5 Ångstroms but in some cases can reach below 2 Å resolution. Systems currently being studied include herpesviruses and dsDNA bacteriophages such as HK97, lambda, D3, T5 and others. These tailed phages have important structural similarities with each other and with animal viruses such as herpesvirus, indicating a long evolutionary connection between them. The dynamic aspects of the virus lifecycle – assembly, DNA packaging, infection, and DNA delivery – are better suited to cryoEM study than crystallography, and the non-symmetric but functionally important regions such as the capsid portal vertex and the phage tail-tip can now be resolved due to recent advances in cryoEM technology. In recent work we imaged the phage HK97 portal vertex where the dodecameric portal ring occupies a 5-fold symmetric vertex of the icosahedral capsid. The portal has several vital functions, including nucleating capsid assembly, packaging and releasing the viral dsDNA, and binding the phage tail assembly. However, the nature of the symmetry mismatch with the capsid has been a long-standing puzzle, but one we could solve by cryoEM visualization to reveal that the capsid protein's scaffold domain interfaces with the portal in a quasi-symmetric 12-10 arrangement. This has a number of implications for capsid assembly and maturation that extend to the herpesviruses. With Fred Homa (Dept. MMG) we have visualized a series of herpesvirus capsid mutants that build a picture of the structural steps involved in DNA packaging and we are applying the phage analysis methods to similarly detail the symmetry-breaking portal vertex. Characterizing the structural and functional repertoire of a virus throughout its lifecycle reveals protein-protein and protein-DNA interactions that could be targeted by highly specific anti-virals. In addition to these viral studies, I am involved with numerous groups to enable their structural investigations of SARS2-Covid 19 (Ambrose/Watkins, Cheng/Shi), GPCRs (Cheng/Xie), encapsulins (NIH), lipid nanoparticles and exosomes (Song, CMU, Duquesne), and Merkel Cell Polyomavirus (Chang/Moore).