Implication of orphan histidine kinase (OhkAsp) in biosynthesis of doxorubicin and daunorubicin in Streptomyces peucetius ATCC 27952

The orphan histidine kinase (HK) from Streptomyces peucetius ATCC 27952 (ohkAsp) was found to be implicated in the regulation of doxorubicin (DOX)/daunorubicin (DNR) biosynthesis, self-defense and developmental attributes. OhkAsp is a homolog of OhkA from Streptomyces coelicolor and Streptomyces avermitilis (with 73 and 75% identity). As in its homologs, S. peucetius mutant with deletion of ohkAsp was found to enhance metabolite biosynthesis and impaired the morphological differentiation. But, unlike its homologs from Streptomyces coelicolor and Streptomyces avermitilis, differential enhancement in level of secondary metabolite production was found in overexpression mutants apart from deletion mutant. The deflection in characteristics of OhkA in its homologue from S. peucetius ATCC 27952, and its imminent implications was monitered by making various mutants with differential expression level of ohkAsp. The variations were observed in the morphology of mutants, transcriptional level of effectors and regulators of DOX/DNR biosynthesis pathway, DOX/DNR precursor pool and biomass accumulation. Based on comparisons of domain arrangements among its homologs, Low Complexity Region (LCR) present on the OhkAsp was the only domain that stood out. Further, the LCR on OhkAsp was found to be overlapping with a putative receiver domain responsible for interaction with response regulator. The imminent implications of differential expression level of ohkAsp on: regulation and biosynthesis of DOX/DNR, morphological differentiation, DOX/DNR precursor pool and biomass accumulation were explored in this study.