Biology 421/521: Virology : Lecture 5, 9 October 2002

Last Updated: 10/10/02 at 4:25 PM

Outline

• Icosahedral symmetry
• Capsid structure
  • Polio virus (Picornaviruses)
  • SV-40 (Papomaviruses)
  • Adenovirus (Large Icosahedral Virus)
• Genome packaging
• Envelopes
• Enzymes
• Other (Viral and Cellular) Proteins

Review

• Quasi-equivalency
• Triangulation numbers
• Figure 3.6/3.7

Turrivirus from Yellowstone T = 31

• h = 5, k = 1

Poliovirus (Picornavirus)

• X-ray crystal structure solved, 1985
• 30 nm particles
• 60 copies of VP1, VP2, VP3, and VP4
• 7.5kb (+) ssRNA genome
• Figure Appendix 1

Polio VP structures

• Very similar structures but different sequences
• Figure 3.8

Polio capsid structure

• Not-quasiequivalent (but close)
• Peaks and valleys (VP1 interactions)
• Figure 3.9

SV-40

• papovavirus, 50 nm
• Appendix Figure 13
• Only one coat protein (VP1)
• 360 subunits: T = 6 ?
• 72 pentamers
• Not symmetric!
• Still beta-barrel structure
  • but in very different place
• Figure 3.10

Herpesviruses

• HUGE! 200 nm
• HSV 1
• Appendix Figure 17
• Single coat protein (of nucleocapsid)
  • 960 copies
  • T = 16
• 80 other proteins in virion
• Teguement and envelope spikes

Adenovirus

• Large (150 nm) NAKED virus
• Appendix Figure 15
• Penton Base and fibers
• Hexons (VP2 trimers)
• Arranged in T = 25 symmetry

Divide and conquer!

• Figure 3.13
• Hexon structure
• Figure 3.12
• Beta-barrels (again)

Difference imaging

• Figure 3.14

Other Large Icosahedral Viruses

• Reo/Rotaviruses
• 2 shells 12 spikes/3 shells 60 spikes
• Reovirus - 80nm
  • Inner core (nucleocapsid)
  • VP7 T = 13
  • inside VP3 T=2?
  • Figure 3.15

Other Animal Viruses

• Maybe combinations of structures
• Vaccinia - Figure 3.16

Packaging the genome

• Direct contact with capsid proteins
• Specialized binding proteins
• Cellular DNA binding proteins
• Table 3.6

Rotavirus genome packaging

• 11 ds RNA segments in T = 3 particle
• 25% of RNA is ordered!
• (not in Herpesvirus)
• Figure 3.17

Other genome packaging strategies

• Specialized viral proteins:
  • Hard to isolate in “packaged form”
  • Generally ribonucleoprotein complexes
  • NC protein in Retroviruses then packaged in Capsid protein
  • Often important for assembly
• Cellular proteins
  • Papovaviruses (SV40)
    • Packaged with histones