Geldanamycin
Encyclopedia
Geldanamycin is a benzoquinone ansamycin
antibiotic
that binds to Hsp90
(Heat Shock Protein 90) and inhibits its function. HSP90 client proteins play important roles in the regulation of the cell cycle, cell growth, cell survival, apoptosis
, angiogenesis
and oncogenesis.
Geldanamycin induces the degradation of proteins that are mutated in tumor
cells such as v-Src, Bcr-Abl and p53
preferentially over their normal cellular counterparts. This effect is mediated via HSP90. Despite its potent antitumor potential, geldanamycin presents several major drawbacks as a drug candidate (namely, hepatotoxicity
) that have led to the development of geldanamycin analogues, in particular analogues containing a derivatisation at the 17 position:
hygroscopicus. It is a macrocyclic polyketide that is synthesized by a Type I polyketide synthase
. The genes gelA, gelB, and gelC encode for the polyketide synthase. The PKS is first loaded with 3-amino-5-hydroxybenzoic acid (AHBA). It then utilizes malonyl-CoA
, methylmalonyl-CoA
, and methoxymalonyl-CoA to synthesize the precursor molecule Progeldanamycin. This precursor is subjected to several enzymatic and non-enzymatic tailoring steps to produce the active molecule Geldanamycin, which include hydroxylation, o-methylation, carbamoylation, and oxidation.
Ansamycin
Ansamycins is a family of secondary metabolites that show antimicrobial activity against many gram-positive and some gram-negative bacteria and includes various compounds, among which: streptovaricins and rifamycins...
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 binds to Hsp90
Hsp90
Hsp90 is a molecular chaperone and is one of the most abundant proteins expressed in cells. It is a member of the heat shock protein family, which is upregulated in response to stress...
(Heat Shock Protein 90) and inhibits its function. HSP90 client proteins play important roles in the regulation of the cell cycle, cell growth, cell survival, apoptosis
Apoptosis
Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Biochemical events lead to characteristic cell changes and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation...
, angiogenesis
Angiogenesis
Angiogenesis is the physiological process involving the growth of new blood vessels from pre-existing vessels. Though there has been some debate over terminology, vasculogenesis is the term used for spontaneous blood-vessel formation, and intussusception is the term for the formation of new blood...
and oncogenesis.
Geldanamycin induces the degradation of proteins that are mutated in tumor
Tumor
A tumor or tumour is commonly used as a synonym for a neoplasm that appears enlarged in size. Tumor is not synonymous with cancer...
cells such as v-Src, Bcr-Abl and p53
P53
p53 , is a tumor suppressor protein that in humans is encoded by the TP53 gene. p53 is crucial in multicellular organisms, where it regulates the cell cycle and, thus, functions as a tumor suppressor that is involved in preventing cancer...
preferentially over their normal cellular counterparts. This effect is mediated via HSP90. Despite its potent antitumor potential, geldanamycin presents several major drawbacks as a drug candidate (namely, hepatotoxicity
Hepatotoxicity
Hepatotoxicity implies chemical-driven liver damage.The liver plays a central role in transforming and clearing chemicals and is susceptible to the toxicity from these agents. Certain medicinal agents, when taken in overdoses and sometimes even when introduced within therapeutic ranges, may injure...
) that have led to the development of geldanamycin analogues, in particular analogues containing a derivatisation at the 17 position:
- 17-AAG
- 17-DMAG
Biosynthesis
Geldanamycin was originally discovered in the organism StreptomycesStreptomyces
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...
hygroscopicus. It is a macrocyclic polyketide that is synthesized by a Type I polyketide synthase
Polyketide synthase
Polyketide synthases are a family of multi-domain enzymes or enzyme complexes that produce polyketides, a large class of secondary metabolites, in bacteria, fungi, plants, and a few animal lineages...
. The genes gelA, gelB, and gelC encode for the polyketide synthase. The PKS is first loaded with 3-amino-5-hydroxybenzoic acid (AHBA). It then utilizes malonyl-CoA
Malonyl-CoA
Malonyl-CoA is a coenzyme A derivative.-Functions:It plays a key role in chain elongation in fatty acid biosynthesis and polyketide biosynthesis....
, methylmalonyl-CoA
Methylmalonyl-CoA
Methylmalonyl-CoA is the coenzyme A linked form of methylmalonic acid. Methylmalonyl-CoA is formed from propionyl-CoA by propionyl-CoA carboxylase by help of biotin . It is converted into succinyl-CoA by methylmalonyl-CoA mutase, in a reaction that requires vitamin B12 as a cofactor...
, and methoxymalonyl-CoA to synthesize the precursor molecule Progeldanamycin. This precursor is subjected to several enzymatic and non-enzymatic tailoring steps to produce the active molecule Geldanamycin, which include hydroxylation, o-methylation, carbamoylation, and oxidation.
External links
- A comprehensive review about Geldanamycin, 17AAG and 17DMAG
- Geldanamycin from FermentekFermentekFermentek Ltd. is a biotechnological company, located in Atarot industrial zone, Jerusalem, Israel, specializing in the research, development and manufacture of biologically active, natural products isolated from microorganisms as well as from other natural sources such as plants and algae.The main...