Fred L. Homa, PhD

Associate Professor


Dr. Homa

Contact

412-648-8788
Fax: 412-624-1401

515 Bridgeside Point II

450 Technology Drive

Pittsburgh, PA 15219-3143

Education

PhD in Biological Chemistry, University of Illinois Medical School

Research Summary

Studies in my lab are primarily focused on understanding the molecular basis of HSV-1 capsid assembly and DNA packaging. Assembly of HSV-1 capsids requires the interaction of the four structural proteins VP5, VP19C, VP23 and VP22a. Encapsidation of viral DNA requires six cleavage/packaging proteins (UL6, UL15, UL17, UL28, UL32, UL33) that interact with the capsid either during capsid assembly or when DNA is packaged. DNA is considered to enter the capsid through the ring-shaped portal (composed of the UL6 protein) present at a unique vertex. The portal is assumed to rotate as DNA enters with energy provided by terminase proteins (UL15 and UL28), which also cut the concatemeric DNA at specific sites to yield a procapsid containing and intact genome. The scaffold protein, VP22a is released from the capsid during the packaging event. The final step in the process is “capsid completion” which results in the formation of a stable DNA-containing capsid. Six HSV-1 proteins (UL6, UL15, UL17, UL28, UL32, and UL33) are required for the cleavage/packaging reaction while the HSV-1 UL25 protein is required for the formation of a stable DNA-containing capsid. The cleavage/packaging and “capsid completion” reactions can be viewed as separate steps in the overall process of generating a stable DNA-containing capsid. The overall goal of the work is to provide a better understanding of these two steps by focusing on the UL28 and UL25 proteins. Based on the importance of UL25 in “capsid completion,” biochemical and genetic studies are aimed at mapping functional domains of UL25 that are important for assembly into capsids, for protein-protein interactions, and protein-nucleic acid interactions. UL28 is a minor capsid protein that is one subunit of the terminase complex and has been shown to interact with UL6, UL15, and UL33. More importantly, UL28 has been shown to specifically bind to HSV-1 packaging sequences (pac1 site). Although, the focus will be on the UL28 protein the aim is to characterize the whole cleavage/packaging complex using a genetic approach to examine how mutations in the UL28 gene affect its interaction with: (i) DNA, (ii) capsid proteins, and (iii) the other cleavage/packaging proteins. By focusing on UL28 the goal is to identify the protein complexes that are essential for the cleavage/packaging reaction. It’s likely that cellular proteins are involved in this process and the focus of the third aim of this proposal is to profile the cleavage/packaging protein complexes that form in infected cells by purification of native complexes from infected cells. A long term goal of our laboratory is to develop an in vitro cleavage and packaging reaction. It is anticipated that the studies in this proposal will not only enhance our understanding of the mechanisms of genome maturation and encapsidation and lead to the development of novel strategies for antiviral therapy.

Research Lab Affiliation

Publications

Nucleocapsid structure, assembly and DNA packaging of herpes simplex virus. In S.K. Weller (ed.), Alphaheresviruses. Caister Academic Press, Norwich, UK. |  

Toropova, K; Huffman, J. B; Homa, F. L; and Conway, J. F. (2011) The herpes simplex virus 1 UL17 protein is the second constituent of the capsid vertex-specific component required for DNA packaging and retention. J Virol. 85: 7513-7522. |  View Abstract

Cockrell, S. K; Huffman, J. B; Toropova, K; Conway, J. F; and Homa, F. L. (2011) Residues of the UL25 protein of herpes simplex virus that are required for its stable interaction with capsids. J Virol. 85: 4875-4887. |  View Abstract

Conway, J. F; Cockrell, S. K; Copeland, A. M; Newcomb, W. W; Brown, J. C; and Homa, F. L. (2010) Labeling and localization of the herpes simplex virus capsid protein UL25 and its interaction with the two triplexes closest to the penton. J Mol Biol. 397: 575-586. |  View Abstract

Cockrell, S. K; Sanchez, M. E; Erazo, A; and Homa, F. L. (2009) Role of the UL25 protein in herpes simplex virus DNA encapsidation. J Virol. 83: 47-57. |  View Abstract

Huffman, J. B; Newcomb, W. W; Brown, J. C; and Homa, F. L. (2008) Amino acids 143-150 of the herpes simplex virus type 1 scaffold protein are required for the formation of portal-containing capsids. J Virol. 82: 6778-6781. |  View Abstract

Jacobson, J. G; Yang, K; Baines, J. D; and Homa, F. L. (2006) Linker insertion mutations in the herpes simplex virus type 1 UL28 gene: effects on UL28 interaction with UL15 and UL33 and identification of a second-site mutation in the UL15 gene that suppresses a lethal UL28 mutation. J Virol. 80: 12312-12323. |  View Abstract