Structure of the Pseudorabies Virus Capsid: Comparison with Herpes Simplex Virus Type 1 and Differential Binding of Essential Minor Proteins

• Published in: Journal of molecular biology 2013-09, Vol.425 (18), p.3415-3428
• Main Authors: Homa, FL, Huffman, JB, Toropova, K, Lopez, HR, Makhov, AM, Conway, JF
• Format: Article
• Language: English
• Subjects: Animals; capsid; Capsid - chemistry; Capsid - metabolism; Capsid - ultrastructure; Capsid Proteins - chemistry; Capsid Proteins - genetics; Capsid Proteins - metabolism; Cells, Cultured; Cercopithecus aethiops; cryo-electron microscopy; Cryoelectron Microscopy; crystal structure; CVSC; green fluorescent protein; Herpes simplex virus 1; Herpesvirus 1, Human - chemistry; Herpesvirus 1, Human - genetics; Herpesvirus 1, Human - physiology; Herpesvirus 1, Human - ultrastructure; Herpesvirus 1, Suid - chemistry; Herpesvirus 1, Suid - genetics; Herpesvirus 1, Suid - physiology; Herpesvirus 1, Suid - ultrastructure; Human herpesvirus 1; mass spectrometry; microscopy; Models, Biological; Models, Molecular; mutants; Protein Binding - genetics; Protein Multimerization - genetics; Protein Multimerization - physiology; Protein Structure, Quaternary; Pseudorabies virus; pUL17; pUL25; Suid herpesvirus 1; Swine; Vero Cells; Viral Proteins - chemistry; Viral Proteins - genetics; Viral Proteins - metabolism; virion; Virus Assembly - physiology; X-radiation
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1016/j.jmb.2013.06.034

The structure of pseudorabies virus (PRV) capsids isolated from the nucleus of infected cells and from PRV virions was determined by cryo-electron microscopy (cryo-EM) and compared to herpes simplex virus type 1 (HSV-1) capsids. PRV capsid structures closely resemble those of HSV-1, including distribution of the capsid vertex specific component (CVSC) of HSV-1, which is a heterodimer of the pUL17 and pUL25 proteins. Occupancy of CVSC on all PRV capsids is near 100%, compared to ~50% reported for HSV-1 C-capsids and 25% or less that we measure for HSV-1 A- and B-capsids. A PRV mutant lacking pUL25 does not produce C-capsids and lacks visible CVSC density in the cryo-EM-based reconstruction. A reconstruction of PRV capsids in which green fluorescent protein was fused within the N-terminus of pUL25 confirmed previous studies with a similar HSV-1 capsid mutant localizing pUL25 to the CVSC density region that is distal to the penton. However, comparison of the CVSC density in a 9-Å-resolution PRV C-capsid map with the available crystal structure of HSV-1 pUL25 failed to find a satisfactory fit, suggesting either a different fold for PRV pUL25 or a capsid-bound conformation for pUL25 that does not match the X-ray model determined from protein crystallized in solution. The PRV capsid imaged within virions closely resembles C-capsids with the addition of weak but significant density shrouding the pentons that we attribute to tegument proteins. Our results demonstrate significant structure conservation between the PRV and HSV capsids. [Display omitted] •We characterize the structure of PRV capsids by cryo-EM.•PRV and HSV-1 capsids appear to be very similar.•The CVSC molecule and pUL25 protein have higher occupancy on PRV capsids than HSV-1.•The HSV-1 pUL25 crystal structure is inconsistent with the PRV cryo-EM density.•PRV capsids offer better stability than HSV-1 for structural studies.