NOMENKLATUR DAN KLASIFIKASI VIRUS

KLASIFIKASI VIRUS

What is the purpose of classification?  Tomakestructuralarrangementforeasy comprehension  To communicate taxonomic decisions to the international community of virologist  Toenablepredictionofproperties of new viruses  Possible evolutionary relationships

Descriptors used in virus Taxonomy  Virion properties  Morphological properties of virion  Size;Shape; presence or absence ofenvelop or peplomers; capsomeric symmetry & structure  Physical properties of the virus  Molecular mass  Buoyant density  Sedimentation coefficient  pH stability, Solvent stability, Radiation stability, detergent stability  Cation (Mg2+, Mn2+, Ca2+) stability

 Properties of genome  Type of nucleic acid  Strandedness of n/acid  Linear or circular  Sense: +ve or –ve or ambisense  Number of segments  Size of genome or genome segments  Presence or absence and type of 5’ terminal cap  Presence o or absence of5’terminal covalently- linked polypeptide  Presence o or absence of 3’terminal poly (A) tract (or other specific tract)  Nucleotide sequence comparisons Descriptors used in virus Taxonomy

 Properties of protein  Number; size; functional activities and Amino acid sequence comparisons  Lipids  Presence or absence; Nature  Carbohydrates  Presence or absence; Nature  Genome organization and replicati on  Genome organization  Strategy of replication of nucleic acid  Characteristics of transcription  Characteristics of translation and post translational processing  Sites of accumulation of virion proteins, site of assembly site of maturation and release  Cytopathology inclusion body formation Descriptors used in virus Taxonomy

 Antigenic properties  Serological relationship  Mapping epitopes  Biological properties  Host range, natural & experimental; pathogenicity, etiology  Tissue tropism, pathology, histopathology,  Mode of transmission in nature; vector relationship;  Geological distribution Descriptors used in virus Taxonomy

Virus Classification Taxonomy from Order downward (three orders now recognized) Family often the highest classification. Ends in -viridae. Many families have subfamilies. Ends in -virinae. Bacterial viruses referred to as bacteriophage or phage (with a few exceptions). Examples family Myoviridae genus T4-like phages type species Enterobacteria phage T4 family Herpesviridae, subfamily Betaherpesvirinae genus Muromegalovirus type species Murine herpesvirus 1

Virus Classification I - the Baltimore classification Was crated by American biologist David Baltimore It is basically based on the method of viral syntesis It groups virus into families according to their type of genome All viruses must produce mRNA, or (+) sense RNA A complementary strand of nucleic acid is (–) sense The Baltimore classification has + RNA as its central point Its principles are fundamental to an understanding of virus classification and genome replication, but it is rarely used as a classification system in its own right

Based on genetic contents and replication strategies of viruses. According to the Baltimore classification, viruses are divided into the following seven classes: 1. dsDNA viruses 2. ssDNA viruses 3. dsRNA viruses 4. (+) sense ssRNA viruses (codes directly for protein) 5. (-) sense ssRNA viruses 6. RNA reverse transcribing viruses 7. DNA reverse transcribing viruses where "ds" represents "double strand" and "ss" denotes "single strand". Virus Classification I - the Baltimore classification

dsDNA Viruses No dsDNA virus is known to infect plants Examples of dsDNA viruses that infect humans –HSV, HPV and adenoviruses Among the largest known viruses Genome size varies from 5 to 1180 Kb Unfragmented genomes Both linear and circular Large genome size attributed to stability of dsDNA Low error rate during replication Phages are dsDNA viruses (95%)

ssDNA Viruses ssDNA Viruses have the following characteristics –Small genome, 2-7 Kb Possibly due to unstable nature of ssDNA compared to dsDNA –Circular genomes with the exception of Parvoviridae (hairpin) –No envelope –Predominantly icosahedral capsids

dsRNA Viruses They utilize RNA dependent polymerase Icosahedral capsids Capsids stays intact inside cell. Why?Genome protection. Transcription occurs via viral RNA polymerases Reoviruses (dsRNA) are capable of infecting multiple species (plants, vertebrates, fungi). Not a common phenomenon. Rhabhoviridae infect multiple species as well The fact that they carry their own RNA replication/transcription proteins makes them more adept

Viruses With + strand RNA Genomes Very common of plant viruses to be + ssRNA Only one phage family is + ssRNA RNA viruses have linear genomes Similar to ssDNA viruses they are susceptible to nucleases and divalant cation degradation Coronavirus has the largest genome of + ssRNA virus (16-30 Kb)

- ssRNA Viruses This group includes some of the deadliest viruses –Ebola, rabies, influenza, measles Only helical nucleocapsids Nucleocapsid seems to provide stability for RNA dependent RNA polymerase to generate + ssRNA + ssRNA=mRNA

Viruses With Reverse Transcription 3 families belong to this group –Retroviridae, Ex. HIV –Hepadnaviridae, Ex. Hep B –Caulimoviridae, Ex. Cauliflower Mosaic Virus These families utilize enzyme that uses an RNA template to make DNA template Reverse transcriptase is packaged in capsid –Similar to + ssRNA and – ssRNA that package the RNA dependent polymerase Retroviruses package 2 copies of their RNA genome in the capsid

Virus classification II - the Classical system This is a based on three principles - 1)that we are classifying the virus itself, not the host 2) the nucleic acid genome 3) the shared physical properties of the infectious agent (e.g capsid symmetry, dimensions, lipid envelope)

Virus classification III - the genomic system More recently a precise ordering of viruses within and between families is possible based on DNA/RNA sequence By the year 2000 there were over 4000 viruses of plants, animals and bacteria - in 71 families, 9 subfamilies and 164 genera

RNA viruses From Principles of Virology Flint et al ASM Press

DNA viruses From Principles of Virology Flint et al ASM Press

Criteria demarcating different virus taxa  Order  Common properties between several families including  Biochemical composition  Viurs replication strategy  Particle structure  General genome organization  Family  Common properties between several families including  Biochemical composition  Virus replication strategy  Nature of particle structure  Genome organization

GenusGenus  Common properties with a genus including:  Virus replication strategy  Genome size, organization and/ or number of segments  Sequence homologies  Vector transmission  Species  Common properties within a including:  Genome rearrangement  Sequence homologies  Serological relationship  Vector transmission  Host range  Pathogenicity  Tissue tropism  Geographical distribution Criteria demarcating different virus taxa

Table 1. Suffixes for taxonomic categories in three codes of nomenclature Suffix Taxon Botanical and bacteriological codes Viral code Subclass -idae--- Order -ales Family -aceae-idae Subfamily -oideae-inae

1. Structure of the virus particle 2. Physicochemical properties particle 3. Properties of viral nucleic acid 4. Viral proteins 5. Serological relationships 6. Activities in the plant 7. Methods of transmission Criteria for classifying plant virus

The families & genera of viruses infecting plants  Plant viruses are diverse, but not as diverse as animal viruses  Probably because of size constraints imposed by requirement to move through cell to cell of plasmodesmata’s host plants

Satellite Viruses Viruses that must always be associated with certain typical viruses (helpers) because they depend on the helper for multiplication and plant infections. They often reduce the ability of the helper virus to multiply and cause disease, so the satellite viruses act as parasites. These viruses require a helper virus Their genomes encode for capsid proteins Nucleic acid satellites are either non-coding or encode for non- capsid proteins Mostly a plant phenomenon In humans the Hep  virus resembles characteristics of satellite virus/viroid

INFECTOUS AGENTS Virion = a complete virus particle, including envelope (if any) Viroid = an infectious RNA particle, smaller than a virus, lacking a capsid, that causes various plant diseases Virusoid (satellite RNA) = same as viroid; small, ssRNA molecule, usually 500 to 2000 nucleotides in length, lacking a capsid, lack genes required for the replication  virusoid require a helper (satellite) virus to replicate, causes various plant diseases.

Example Viroid - avocado sunblotch viroid, peach latent mosaic, potato spindle tuber, coconut cadang-cadang, tomato plant macho viroid, citrus bent leaf viroid, pear blister canker viroid -Virusoid - barley yellow dwarf satellite RNA, tobacco ringspot virus satellite RNA Viroid - cause lethal plant diseases; potato spindle tuber disease, chrysanthemum stunt disease, cucumber pale fruit disease, coconut cadang-cadang disease, chrysanthemum stunt disease, tomato apical stunt disease. Virusoid - cause tobacco necrosis Disease

PRIONS A unique infectious agent, protein infectious particle Prion = a small infectious particle consisting of protein and lack nucleic acid. Prion – features: -Resistant to inactivation by heating to 90 o C, which inactivate virus -The infection is not sensitive to radiation; radiation damages virus genomes -Prions are not destroyed by enzymes that digest nucleic acids -Sensitive to protein denaturing agents; urea, phenol -Prions have direct pairing of amino acids

Diseases – 1.Creutzfeldt-Jakob – mental degeneration, loss of motor function and death (human) 2.Scrapie and bovine spongiform encephalopathy (BSE) – loss of neuronal function that leads to death in sheep and dairy cattle. 3.Kuru – a neurological disorder in human Holes brain – “spongiform” Cerebral cortex of a normal human brain (right), patient with CJD (left). Once present in the brain, prions cause normal proteins to refold into abnormal shapes. As these abnormal proteins multiply, they destroy neurons and eventually cause brain tissue to become riddled with holes. Prions can only be destroyed through incineration. PRIONS

Virus, Viroid and Prion  Characteristic between virus, viroid and prion  Nucleic acid type, NA strandedness, host range and structural features

NOMENKLATUR VIRUS

How are viruses named? Based on: - The disease they cause poliovirus, rabies virus - The type of disease murine leukemia virus - Geographic locations Sendai virus, Coxsackie virus - Their discovers Epstein-Barr virus - How they were originally thought to be contracted Tobacco mosaic virus, dengue virus ( “ evil spirit ” ), influenza virus (the “ influence ” of bad air) - Combinations of the above Rous Sarcoma virus

 Latinbinomialswereproposedfirst by Holmes in 1939  Various other schemes proposed between 1940 and 1966  International Committee on the Nomenclature of Viruses (ICNV) (1966)  Naming and cataloguing of viruses.  Renamed:InternationalCommittee Taxonomy of Viruses (ICTV) in 1973.

The International Committeeon Taxonomyof Viruses(ICTV)hasframed20 nomenclature. Amongothers rulesforvirus itrecognizes commonnames,theirinternationalmeaningand use of existing names.  ICTV database (ICTVdb)- A centralized repository of virus information  Collectinformationfrom databases around the world.  Facilitated the job of accurate identification and diagnosis of new and important virus diseases.

Terima Kasih