Elucidation of the Functional Metal Binding Profile of a Cd^II/Pb^II Sensor CmtR^Sc from Streptomyces coelicolor

Abstract

Metal homeostasis and resistance in bacteria is maintained by a panel of metal sensing transcriptional regulators that collectively control transition metal availability and mediate resistance to heavy metal xenobiotics, including AsIII, CdII, PbII and HgII. The ArsR family constitutes a superfamily of metal sensors that appear to conform to the same winged helical, homodimeric fold, that collectively “sense” a wide array of beneficial metal ions and heavy metal pollutants. The genomes of many actinomycetes, including the soil dwelling bacterium Streptomyces coelicolor and the human pathogen Mycobacterium tuberculosis, encode over ten ArsR family regulators, most of unknown function. Here, we present the characterization of a homolog of M. tuberculosis CmtR (CmtRMtb) from S. coelicolor, denoted CmtRSc. We show that CmtRSc, in contrast to CmtRMtb binds two monomer mol equivalents of PbII or CdII to form two pairs of trigonal S3 coordination complexes per dimer. Metal site 1 conforms exactly to the α4C site previously characterized in CmtRMtb while metal site 2 is coordinated by a C-terminal vicinal thiolate pair, Cys110 and Cys111. Biological assays reveal that only CdII and, to a lesser extent, PbII mediate transcriptional derepression in the heterologous host M. smegmatis in a way that requires metal site 1. In contrast, mutagenesis of metal site 2 ligands Cys110 or Cys111 significantly reduces CdII responsiveness, with no detectable effect on PbII sensing. The implications of these findings on the ability to predict metal specificity and function from metal-site “signatures” in the primary structure of ArsR family proteins are discussed.

MALDI-TOF-MS and 16S rRNA characterization of lead tolerant metallophile bacteria isolated from saffron soils of Kashmir for their sequestration potential

“…Microorganism present in soil and water has the ability to produce volatile compounds that are less toxic from organic and inorganic leading compounds ( Kohli et al, 2019 , Abd_Allah et al, 2019 ) and it can be attributed to the present study. For the proper growth in presence of metals these species may have created a protective system as an additional component in relation to cytochrome c in the ultimate part of the respiratory chain, which is not inactivated by the metal ( Wang et al, 2010 , Lima e Silvaet al, 2012 ). Lead resistance in the microorganisms is also acquired by limiting their movement across the cell envelope ( Rahman et al, 2019 ).…”

Antimicrobial Nanomaterials: Why Evolution Matters

“…Homeostasis is a self-regulating core feature of biological organisms that allows them to, whenever possible, maintain their internal stability and keep a constant physiological state. There are a number of homeostatic process that must be preserved in order to guarantee the survival of the organism including iron homeostasis, metal homeostasis, pH homeostasis and membrane and lipid homeostasis [ 4 , 5 , 6 , 7 , 8 ]. Since the beginning of life on this planet, microbes have been exposed to metals—some necessary, but many that are toxic to the cells [ 9 ].…”

“…Virtually all bacteria have acquired genes that control their physiology, allowing them to resist toxic metal ions (Ag + , Cd 2+ , Hg 2+ , Ni 2+ etc.). To deal with these toxic metals, many bacteria express metal-sensing transcriptional regulators that can sense both beneficial and toxic metals allowing them to adapt to their environments rather quickly and as a result, energy dependent efflux is the most commonly deployed metal resistance mechanism among microorganisms [ 5 , 9 ]. Our studies showed this for both ionic and nanosilver (Ag + ) based resistance in E. coli [ 2 , 10 ].…”

An overview on transcriptional regulators in Streptomyces

“…ArsR/SmtB family 1147 Under conditions of metal excess, members of the ArsR/SmtB family 1148 regulate intracellular metal-ion concentrations by functioning as 1149 metallo-regulatory sensors (reviewed in [32]). In contrast to other clas-1150ses of prokaryotic metal sensors, the ArsR/SmtB members seem to func-1151 tion exclusively as transcriptional repressors[279,280].…”