Deoxysugar Transfer during Chromomycin A ₃ Biosynthesis in Streptomyces griseus subsp. griseus : New Derivatives with Antitumor Activity

Abstract

Chromomycin A 3 (Fig. 1A) is an antitumor drug produced by Streptomyces griseus and other streptomycete species. It belongs to the class of antitumor compounds of the aureolic acid family (22), which inhibit growth and multiplication of several tumor cell lines. The antitumor properties are ascribed to their inhibitory effects on replication and transcription processes during macromolecular biosynthesis by interacting, in the presence of Mg 2ϩ , with GC-rich nucleotide sequences located in the minor groove of DNA. In this respect, they have been shown to prevent resistance to other antitumor agents by a number of mechanisms, including downregulation of proteins, such as MDR1 (16, 28). Chromomycin and the closely related compound mithramycin were also found to stimulate K562 cell erythroid differentiation (3), to be potent inhibitors of neuronal apoptosis (7), and to have antiviral activity against human immunodeficiency virus type 1 (2).Structurally, chromomycin A 3 is related to mithramycin.Both consist of a tricyclic chromophore (aglycone) with two aliphatic side chains attached at C-3 and C-7. However, they differ in glycosylation pattern. In chromomycin, the carbohydrate moieties and the acetyl groups which decorate these sugars are major structural contributors to the biological activity. Thus, it has been shown that the acetyl groups in sugars A and E of chromomycin contribute distinctively in the DNA complex formation by providing additional H bond acceptor groups that interact with the 2-amino groups of G-bases, thus adding more specificity to DNA binding (6). Also, it has been recently demonstrated that elimination of acetyl groups leads to the generation of a chromomycin derivative with a significant decreased antitumor activity (14).We have recently reported the cloning and characterization of the chromomycin A 3 biosynthetic gene cluster (15). Because mithramycin and chromomycin share the same aglycone but differ in four of the five sugars attached to the aglycone, we were interested in characterizing the chromomycin glycosyltransferase genes. These genes together with those of the mithramycin cluster may serve as genetic tools for further studies on the generation of novel aureolic acid group derivatives with potential antitumor activity. Here we report the identification * Corresponding author. Mailing address for Carmen Méndez (molecular biological questions):

Characterization of the Terminal Activation Step Catalyzed by Oxygenase CmmOIV of the Chromomycin Biosynthetic Pathway from Streptomyces griseus

“…The structure of 11 matches earlier discussions that concluded that CmmGIV, the glycosyltransferase responsible for the transfers of both sugars A and E, actually transfers 4-ketosugars, which are reduced after the attachment, presumably by CmmTIII (10). Thus, compound 11 might indeed be an (instable) intermediate of the chromomycin A 3 biosynthetic pathway.…”

“…The isolation of compounds from inactivation of CmmA and CmmMIII yielded chromomycin A 3 derivatives with missing acetyl and methyl decorations, and the di-deacetyl-chromomycin A 3 appears to be a substrate for the out-transporters CmrAB (26). On the other hand, mutants in which glycosyltransfer steps affecting sugar units B alone or both A and B, respectively, were inactivated and yielded still tricyclic tetrasaccharidal and tetracyclic trisaccharidal prechromomycins with already O -acetylated sugar moieties A and/or E (10). While these contradictive results could be explained by substrate flexibility of the sugar decorating enzymes, a potential substrate flexibility of key oxygenase CmmOIV is an alternative.…”

Modification of the antibiotic olivomycin I at the 2′-keto group of the side chain. Novel derivatives, antitumor and topoisomerase I-poisoning activity

“…In the past decades, a number of aureolic acid analogs were obtained from genetically engineered mutant producers showing distinct structural changes. [5][6][7][8] This has yielded in some information on the structure-activity relationship of this type of compounds.…”

Comparative Analyses of Gene Clusters and Ks-alpha Genes Involved in the Biosynthesis of Chromomycin A3 and Mithramycin

“…Later, it was identified that premithramycin B was transformed into an aureolic acid structure by oxygenase MtmOIV through fourth ring Baeyer-Villiger oxidative cleavage [26] . The enzyme homologue to cyclase MtmOIV was also identified in the biosynthetic gene cluster of chromomycin A 3 [2] derived from prechromomycin B, which is a tetracylic intermediate [27] .…”