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MORFOLOGI, KOMPONEN
DAN STRUKTUR VIRUS
TUMBUHAN
Keutamaan
Ilmu yang mempelajari struktur virus penting
untuk memahami berbagai aspek virologi,
seperti bagaimana virus bertahan hidup,
menginfeksi,
menyebar,
bereplikasi
dan
bagaimana mereka berhubungan atu sama lain.
Ilmu tentang struktur virus telah meningkat
sejak penemuan mikroskop elektron dan
prosedur X-ray crystallography seperti;
 Teknik molekuler
 Informasi kimia tentang virus
Ultrastruktur Virus
Istilah pada komponen virus
Kapsid: kulit luar protein yang melingkupi
asam nukleat
 Kapsomer: unit morfologi yang dilihat dari
permukaan partikel dan mewakili klaster unit
struktur
 Virion : partikel lengkap partikel virus

Istilah pada komponen virus
Amplop (envelope/viral membrane): zat
lemak berlapis yang mengandung glikoprotein
virus. Tidak semua virus memiliki amplop,
beberapa virus hanya terdiri dari nuklekapsid.
 Nukleokapsid (core): asam nukleat virus
yang dibungkus oleh pelindung kapsid protein

Viruses
Figure 13.1
Virus Structures
1. contain DNA or RNA
2. contain a protein coat (capsid)
3. Receptor – on capsid determines what cell
can be infected and how the virus infects the cell
Virus Structures
Inner core nucleic acid
 Contains genetic materials (DNA or RNA)
Outer core nucleic acid
Surrounds virus (Capsdi)
 Contains receptors
Structures not found on every viruses
Envelope
Tail, end plate, tail fibres
• Surround some animal viruses
• Made from host membranes
• Bacteriophage only
Struktur Virus
Characteristic size scale is
30-100 nm.
Structures are known at
“atomic resolution” - see
Viper website
(http://viperdb.scripps.edu/
Highly symmetric
(Baker et al.)
Organization of Viral Particles
•Contains RNA or DNA
Streptococcus
•Form a protective package
E. coli
•Transmit genetic material
•Entry, multiply and exit the
host
•Redirect cellular machinery
Yeast Cell
Principles of Viral Architecture
•Viral capsid are made of repated protein subunits
•Capsids are self assembled
•Fraenkel-Conrat and Williams (1955): self-assembly of TMV
•Proteins and nucleic acids are held together with noncovalent bonds
•Protein-protein, protein-nucleic acid, protein-lipid
•Helical or icosahedral symmetry
General Structure of Viruses
• Capsids
– All viruses have capsids - protein coats that enclose
and protect their nucleic acid.
– Each capsid is constructed from identical subunits
called capsomers made of protein.
–The capsid together with the nucleic acid are
nucleoscapsid.
The Viral Capsid
Capsid functions
1. Protect genome from atmosphere (May include damaging
UV-light, shearing forces, nucleases either leaked or
secreted by cells).
2. Virus-attachment protein- interacts with cellular receptor to
initiate infection.
3. Delivery of genome in infectious form. May simply “dump”
genome into cytoplasm (most +ssRNA viruses) or serve as
the core for replication (retroviruses and rotaviruses).
Viral Capsids
• If 1 protein for 1 capsid:
– Need > 18,000 amino acids.
– Need > 54,000 nucleotides.
– Small viruses hold max. of 5,000 nucleotides.
• Must use many copies of 1 (or a few) protein(s).
• High symmetry
– Minimizes # different subunit interactions involved
with assembly.
– Simpler protein.
– Self assembly:
• Self-contained assembly "instructions".
Capsid and Envelope
Non-enveloped
Helical
Icosahedral
Capsid:
•Protect viral nucleic acid
•Interact with the nucleic acid for
packaging
•Interact with vector for specific
transmission
•Interact with host receptors for entry
to cell and to release of nucleic acid
Enveloped
Envelope:
•Made from host cell
membrane (plasma,
ER or Golgi)
•Fuse for Entry
Bentuk Virus
 Kira-kira
½ dari semua virus tumbuhan
yang telah diketahui berbentuk
memanjang (benang berputar atau
batang keras).
 Kira-kira ½ dari semua virus tumbuhan
berbentuk bola (isometris atau
polyhedral).
 Beberapa virus berbentuk basilus
silindris-menyerupai batang.
Bentuk Virus
• CUBIC (Icosahedral/polyhedral):
Spherical, amount of nucleic acid that
can be packaged is limited by the
number of capsomers and the size of
the viral particle
E.g. Papilloma virus
Bentuk Virus
• HELICAL:
Rod shaped, varying widths and specific
architectures; no theoretical limit to the
amount of nucleic acid that can be
packaged
Bentuk Virus
• BACTERIOPHAGE
Polyhedral-shape head
cylindrical tail leglike fibres
Cubic (Icosahedral)
• Susunan Icosahedral adalah struktur virus yang
khas
• Suatu cosahedron memiliki 20 sisi segitiga, 12
sudut, dan 5:3:2 axis simetri rotasi
Helical
• Organized around a single axis (the “helix axis”)
• Probably evolved along with other helical structures like
DNA, -helix, etc.
• Allow flexibility (bending)
• Helical viruses form a closely related spring like helix
instead. The best studied TMV but many animal viruses
and phage use this general arrangement.
– Note-all animal viruses that are helical are enveloped, unlike many of the
phage and plant viruses.
• Most helixes are formed by a single major protein arranged
with a constant relationship to each other (amplitude and
pitch).
Helical symmetry
• Tobacco mosaic virus is typical, well-studied example
• Each particle contains only a single molecule of RNA (6395 nucleotide
residues) and 2130 copies of the coat protein subunit (158 amino acid
residues; 17.3 kilodaltons)
– u=16.33 subunits/turn
– p=1.4 Å
– P= 23 Å
• TMV protein subunits + nucleic acid will self-assemble in vitro in a
energy-independent fashion
• Self-assembly also occurs in the absence of RNA
TMV rod is 18 nanometers
(nm) X 300 nm
n
Komposisi Virus
1.
Protein  adalah 60-95% terdiri dari virion

Sama untuk setiap jenis virus tetapi bervariasi dari satu
virus dgn virus lain


Subunit TMV - 158 asam amino dgn massa 17,600 Dalton
(17.6 kDa, kd atau K)
TYMV – 20,600 Dalton protein
2. Asam nukleat  adalah 5-40% virion
Sphererical viruses: 20-40%
• Helical viruses : 5-6%
•
Komposisi Virus



Asam Nukleat (5-40%) mewakili bahan
genetika, sangat diperlukan untuk replikasi
Asam Nukleat sendiri cukup untuk replikasi
virus
Protein (60-95%) melindungi genom virus
dari:



degradasi
Fasilitasi pergerakan melalui inang dan
transmisi dari satu inang ke inang lainnya.
Persentase protein pada beberapa virus
Persentase protein pada beberapa virus
Virus
n/a (%)
Protein (%)
TMV
5
95
PVX
6
94
PVY
5
95
CpMV
31-33
67-69
CMV
18
82
TRSV
40
60
Watson and Crick
 Pada tahun 1956 mengemukakan:
Jumlah asam nukleat virus tidak cukup untuk mengkodekan lebih dari sejumlah protein
 Oleh karena itu kulit luar protein harus merupakan
subunit yang sama.
 Subunit harus disusun untuk menyediakan setiap
subunit dengan lingkungan yang sama, seperti
pembungkusan simetris.
Berbagai fitur virus dapat di-estimasi
dengan mempelajari:
1. Kimia dan Biokimia
2. Ukuran partikel
•
•
•
•
Hidrodinamika
Pemancaran laser telah digunakan untuk
menentukan radius virus yang berbentuk bola
(spherical virus)
Mikroskop elektron
X-ray crystallography

Dapat memberi estimasi akurat radius virus isokahedral
(icosahedral virus), tapi dgn kondisi virus harus mampu
membentuk kristal yang stabil.
Mikroskop Elektron




Pada tahun 1924 L. de BROGLIE menemukan cahaya
elektron dengan karakter panjang gelombang, yang
kemudian menjadi syarat konstruksi mikroskop elektron.
Ditemukan oleh M. KNOLL & E. RUSKA (Technische
Universität Berlin, 1932).
Salah satu objek biologi yang pertama diamati adalah :
tobacco mosaic virus (TMV).
Gambar sel pertama dipublikasi tahun 1945 oleh K. R.
PORTER, A. CLAUDE dan E. F. FULLAM
(Rockefeller Institute, New York).
The Transmission Electron Microscope (TEM)
The Scanning electron microscope (SEM)
The Transmission Electron Microscope (TEM)
A 1973 Siemens electron microscope EM developed by E. Ruska 1933
The Transmission Electron Microscope (TEM)
Flu virus by TEM
Avian Flu virus by TEM
Swine Flu virus by TEM
TMV by TEM
TMV by SEM
Tobacco necrosis virus, 26 nm in diameter
BROME MOSAIC VIRUS
•Type
member of the
Bromovirus genus, family
Bromoviridae
•Virions are nonenveloped
icosohedrals (T=3), 26 nm
in diameter, contain 22%
nucleic acid and 78% protein
•BMV genome is composed
of three positive sense RNAs
separately encapsidated
RNA1 RNA2 RNA3
RNA4
RNA1
(3.2 kb),
kb),
RNA3 (2.1
(0.9 kb)
RNA2 (2.9
kb), RNA4
Francki, Milne & Hatta. 1985 Atlas of Plant Viruses, vol. I.
Three-dimensional image of Turnip yellow mosaic virus (TYMV)
reconstructed from EM
Tobacco mosaic virus
First virus crystallized (1946 Stanley was
awarded the Nobel prize)
 First demonstration
of
infectious
RNA (1950s)
 First virus to be shown to consist of RNA
and protein
 First virus characterized
by
X-ray
crystallography to show a helical structure
 First virus genome
to
be
completely sequenced

Tobacco mosaic virus (TMV), 300 nm
Potato virus Y (PVY), 740 nm
Maize streak virus,
Geminiviridae
Cocoa swollen shoot virus,
Badnavirus