Kasugamycin
Encyclopedia
Kasugamycin is an aminoglycoside
antibiotic
that was originally isolated in 1965, from Streptomyces kasugaensis, a Streptomyces
strain found near the Kasuga shrine in Nara, Japan
. Kasugamycin was discovered by Hamao Umezawa
, who also discovered kanamycin
and bleomycin
, as a drug which could prevent growth of a fungus causing rice blast disease. It was later found to inhibit bacterial growth also. It exists as a white, crystalline substance with the chemical formula C14H28ClN3O10 (kasugamycin hydrochloride). It is also known as kasumin.
, kasugamycin inhibits proliferation of bacteria by tampering with their ability to make new proteins
, the ribosome
being the major target. Kasugamycin inhibits protein synthesis at the step of translation
initiation. Kasugamycin inhibition is thought to occur by direct competition with initiator transfer RNA
. Recent experiments suggest that kasugamycin indirectly induces dissociation of P-site-bound fMet-tRNAfMet from 30S subunits through perturbation of the mRNA, thereby interfering with translation initiation.
Kasugamycin specifically inhibits translation initiation of canonical but not of leaderless mRNA. For initiation on leaderless mRNA, the overlap between mRNA and kasugamycin is reduced and the binding of tRNA is further stabilized by the presence of the 50S subunit, minimizing Ksg efficacy.
Kasugamycin also induces the formation of unusual 61S ribosomes in vivo, which are proficient in selectively translating leaderless mRNA. 61S particles are stable and are devoid of more than six proteins of the small subunit, including the functionally important proteins S1 and S12.
of kasugamycin in complex with the Escherichia coli 70S ribosome has been determined at 3.5-A resolution. The structure reveals that the drug binds within the messenger RNA channel of the 30S subunit between the universally conserved G926 and A794 nucleotides in 16S ribosomal RNA
, which are sites of kasugamycin resistance. The kasugamycin binding sites are present on top of helix 44 (h44), spanning the region between h24 and h28, which contacts the conserved nucleotides A794 and G926. Neither binding position overlaps with P-site tRNA. Instead, kasugamycin mimics the codon nucleotides at the P and E sites by binding within the path of the mRNA, thus perturbing the mRNA-tRNA codon-anticodon interaction.
in the 16S rRNA methyltransferase
KsgA which methylates
the nucleotides A1518 and A1519 in 16S rRNA. Spontaneous ksgA mutations conferring a modest level of resistance to kasugamycin occur at a high frequency of 10–6. Once cells acquire the ksgA mutations, they produce high-level kasugamycin resistance at an extraordinarily high frequency (100-fold greater frequency than that observed in the ksgA+ strain).
Surprisingly, kasugamycin resistance mutations do not inhibit binding of the drug to the ribosome. Present structural and biochemical results indicate that inhibition by kasugamycin and kasugamycin resistance are closely linked to the structure of the mRNA at the junction of the peptidyl-tRNA and exit-tRNA sites (P and E sites).
Aminoglycoside
An aminoglycoside is a molecule or a portion of a molecule composed of amino-modifiedsugars.Several aminoglycosides function as antibiotics that are effective against certain types of bacteria...
antibiotic
Antibiotic
An antibacterial is a compound or substance that kills or slows down the growth of bacteria.The term is often used synonymously with the term antibiotic; today, however, with increased knowledge of the causative agents of various infectious diseases, antibiotic has come to denote a broader range of...
that was originally isolated in 1965, from Streptomyces kasugaensis, a Streptomyces
Streptomyces
Streptomyces is the largest genus of Actinobacteria and the type genus of the family Streptomycetaceae. Over 500 species of Streptomyces bacteria have been described. As with the other Actinobacteria, streptomycetes are gram-positive, and have genomes with high guanine and cytosine content...
strain found near the Kasuga shrine in Nara, Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
. Kasugamycin was discovered by Hamao Umezawa
Hamao Umezawa
was a Japanese scientist who discovered several antimicrobial agents and enzyme inhibitors.After graduating from the Musashi Junior and Senior High School, Umezawa completed his medical degree in 1937. After serving in Japanese army during World War II Umezawa did work on tuberculosis which led to...
, who also discovered kanamycin
Kanamycin
Kanamycin sulfate is an aminoglycoside antibiotic, available in oral, intravenous, and intramuscular forms, and used to treat a wide variety of infections. Kanamycin is isolated from Streptomyces kanamyceticus.-Mechanism:...
and bleomycin
Bleomycin
Bleomycin is a glycopeptide antibiotic produced by the bacterium Streptomyces verticillus. Bleomycin refers to a family of structurally related compounds. When used as an anticancer agent, the chemotherapeutical forms are primarily bleomycin A2 and B2. It works by causing breaks in DNA...
, as a drug which could prevent growth of a fungus causing rice blast disease. It was later found to inhibit bacterial growth also. It exists as a white, crystalline substance with the chemical formula C14H28ClN3O10 (kasugamycin hydrochloride). It is also known as kasumin.
Mechanism of action
Like many of the known natural antibioticsAntibiotic
An antibacterial is a compound or substance that kills or slows down the growth of bacteria.The term is often used synonymously with the term antibiotic; today, however, with increased knowledge of the causative agents of various infectious diseases, antibiotic has come to denote a broader range of...
, kasugamycin inhibits proliferation of bacteria by tampering with their ability to make new proteins
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
, the ribosome
Ribosome
A ribosome is a component of cells that assembles the twenty specific amino acid molecules to form the particular protein molecule determined by the nucleotide sequence of an RNA molecule....
being the major target. Kasugamycin inhibits protein synthesis at the step of translation
Translation
Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. Whereas interpreting undoubtedly antedates writing, translation began only after the appearance of written literature; there exist partial translations of the Sumerian Epic of...
initiation. Kasugamycin inhibition is thought to occur by direct competition with initiator transfer RNA
Transfer RNA
Transfer RNA is an adaptor molecule composed of RNA, typically 73 to 93 nucleotides in length, that is used in biology to bridge the three-letter genetic code in messenger RNA with the twenty-letter code of amino acids in proteins. The role of tRNA as an adaptor is best understood by...
. Recent experiments suggest that kasugamycin indirectly induces dissociation of P-site-bound fMet-tRNAfMet from 30S subunits through perturbation of the mRNA, thereby interfering with translation initiation.
Kasugamycin specifically inhibits translation initiation of canonical but not of leaderless mRNA. For initiation on leaderless mRNA, the overlap between mRNA and kasugamycin is reduced and the binding of tRNA is further stabilized by the presence of the 50S subunit, minimizing Ksg efficacy.
Kasugamycin also induces the formation of unusual 61S ribosomes in vivo, which are proficient in selectively translating leaderless mRNA. 61S particles are stable and are devoid of more than six proteins of the small subunit, including the functionally important proteins S1 and S12.
Structural basis for kasugamycin action
The X-ray structureX-ray crystallography
X-ray crystallography is a method of determining the arrangement of atoms within a crystal, in which a beam of X-rays strikes a crystal and causes the beam of light to spread into many specific directions. From the angles and intensities of these diffracted beams, a crystallographer can produce a...
of kasugamycin in complex with the Escherichia coli 70S ribosome has been determined at 3.5-A resolution. The structure reveals that the drug binds within the messenger RNA channel of the 30S subunit between the universally conserved G926 and A794 nucleotides in 16S ribosomal RNA
Ribosomal RNA
Ribosomal ribonucleic acid is the RNA component of the ribosome, the enzyme that is the site of protein synthesis in all living cells. Ribosomal RNA provides a mechanism for decoding mRNA into amino acids and interacts with tRNAs during translation by providing peptidyl transferase activity...
, which are sites of kasugamycin resistance. The kasugamycin binding sites are present on top of helix 44 (h44), spanning the region between h24 and h28, which contacts the conserved nucleotides A794 and G926. Neither binding position overlaps with P-site tRNA. Instead, kasugamycin mimics the codon nucleotides at the P and E sites by binding within the path of the mRNA, thus perturbing the mRNA-tRNA codon-anticodon interaction.
Resistance
Low level resistance to kasugamycin is acquired by mutationsMutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...
in the 16S rRNA methyltransferase
Methyltransferase
A methyltransferase is a type of transferase enzyme that transfers a methyl group from a donor to an acceptor.Methylation often occurs on nucleic bases in DNA or amino acids in protein structures...
KsgA which methylates
Methylation
In the chemical sciences, methylation denotes the addition of a methyl group to a substrate or the substitution of an atom or group by a methyl group. Methylation is a form of alkylation with, to be specific, a methyl group, rather than a larger carbon chain, replacing a hydrogen atom...
the nucleotides A1518 and A1519 in 16S rRNA. Spontaneous ksgA mutations conferring a modest level of resistance to kasugamycin occur at a high frequency of 10–6. Once cells acquire the ksgA mutations, they produce high-level kasugamycin resistance at an extraordinarily high frequency (100-fold greater frequency than that observed in the ksgA+ strain).
Surprisingly, kasugamycin resistance mutations do not inhibit binding of the drug to the ribosome. Present structural and biochemical results indicate that inhibition by kasugamycin and kasugamycin resistance are closely linked to the structure of the mRNA at the junction of the peptidyl-tRNA and exit-tRNA sites (P and E sites).