Ivan I Gusarov, Ph.D.

Nitric Oxide protects Gram-positive bacteria against a wide spectrum of antimicrobials
Gusarov, I
2010 JUN ;22(9):S23-S23, Nitric oxide : biology & chemistry
— id: 111897, year: 2010, vol: 22, page: S23, stat: Journal Article,

Endogenous nitric oxide protects bacteria against a wide spectrum of antibiotics
Gusarov, Ivan; Shatalin, Konstantin; Starodubtseva, Marina; Nudler, Evgeny
2009 Sep 11;325(5946):1380-1384, Science
Bacterial nitric oxide synthases (bNOS) are present in many Gram-positive species and have been demonstrated to synthesize NO from arginine in vitro and in vivo. However, the physiological role of bNOS remains largely unknown. We show that NO generated by bNOS increases the resistance of bacteria to a broad spectrum of antibiotics, enabling the bacteria to survive and share habitats with antibiotic-producing microorganisms. NO-mediated resistance is achieved through both the chemical modification of toxic compounds and the alleviation of the oxidative stress imposed by many antibiotics. Our results suggest that the inhibition of NOS activity may increase the effectiveness of antimicrobial therapy
— id: 102402, year: 2009, vol: 325, page: 1380, stat: Journal Article,

Bacterial NO-synthases operate without a dedicated redox partner
Gusarov, Ivan; Starodubtseva, Marina; Wang, Zhi-Qiang; McQuade, Lindsey; Lippard, Stephen J; Stuehr, Dennis J; Nudler, Evgeny
2008 May 9;283(19):13140-13147, Journal of biological chemistry
Bacterial NO-synthases (bNOSs) are smaller than their mammalian counterparts. They lack an essential reductase domain that supplies electrons during NO biosynthesis. This and other structural peculiarities have raised doubts about whether bNOSs were capable of producing NO in vivo. Here we demonstrate that bNOS enzymes from Bacillus subtilis and Bacillus anthracis do indeed produce NO in living cells and accomplish this task by hijacking available cellular redox partners that are not normally committed to NO production. These 'promiscuous' bacterial reductases also support NO synthesis by the oxygenase domain of mammalian NOS expressed in E. coli. Our results suggest that bNOS is an early precursor of eukaryotic NOS and that it acquired its dedicated reductase domain later in evolution. This work also suggests that alternatively spliced forms of mammalian NOSs lacking their reductase domains could still be functional in vivo. On a practical side, bNOS-containing probiotic bacteria offer a unique advantage over conventional chemical NO-donors in generating continuous, readily controllable physiological levels of NO, suggesting a possibility of utilizing such live NO-donors for research and clinical needs
— id: 76130, year: 2008, vol: 283, page: 13140, stat: Journal Article,

Bacillus anthracis-derived nitric oxide is essential for pathogen virulence and survival in macrophages
Shatalin, Konstantin; Gusarov, Ivan; Avetissova, Ekaterina; Shatalina, Yelena; McQuade, Lindsey E; Lippard, Stephen J; Nudler, Evgeny
2008 Jan 22;105(3):1009-1013, Proceedings of the National Academy of Sciences of the United States of America
Phagocytes generate nitric oxide (NO) and other reactive oxygen and nitrogen species in large quantities to combat infecting bacteria. Here, we report the surprising observation that in vivo survival of a notorious pathogen-Bacillus anthracis-critically depends on its own NO-synthase (bNOS) activity. Anthrax spores (Sterne strain) deficient in bNOS lose their virulence in an A/J mouse model of systemic infection and exhibit severely compromised survival when germinating within macrophages. The mechanism underlying bNOS-dependent resistance to macrophage killing relies on NO-mediated activation of bacterial catalase and suppression of the damaging Fenton reaction. Our results demonstrate that pathogenic bacteria use their own NO as a key defense against the immune oxidative burst, thereby establishing bNOS as an essential virulence factor. Thus, bNOS represents an attractive antimicrobial target for treatment of anthrax and other infectious diseases
— id: 75858, year: 2008, vol: 105, page: 1009, stat: Journal Article,

Instant adaptation to oxidative stress in bacteria is mediated by NO
Gusarov, I; Nudler, E
2006 JUN ;14(4):A2-A2, Nitric oxide : biology & chemistry
— id: 64819, year: 2006, vol: 14, page: A2, stat: Journal Article,

NO-mediated cytoprotection: instant adaptation to oxidative stress in bacteria
Gusarov, Ivan; Nudler, Evgeny
2005 Sep 27;102(39):13855-13860, Proceedings of the National Academy of Sciences of the United States of America
Numerous sophisticated systems have been described that protect bacteria from increased levels of reactive oxygen species. Although indispensable during prolonged oxidative stress, these response systems depend on newly synthesized proteins, and are hence both time and energy consuming. Here, we describe an 'express' cytoprotective system in Bacillus subtilis which depends on nitric oxide (NO). We show that NO immediately protects bacterial cells from reactive oxygen species by two independent mechanisms. NO transiently suppresses the enzymatic reduction of free cysteine that fuels the damaging Fenton reaction. In addition, NO directly reactivates catalase, a major antioxidant enzyme that has been inhibited in vivo by endogenous cysteine. Our data also reveal a critical role for bacterial NO-synthase in adaptation to oxidative stress associated with fast metabolic changes, and suggest a possible role for NO in defending pathogens against immune oxidative attack
— id: 76138, year: 2005, vol: 102, page: 13855, stat: Journal Article,

Novel mechanism of bacterial oxidative stress defense activation by NO
Gusarov, I; Nudler, E
2004 AUG ;11(1):61-61, Nitric oxide : biology & chemistry
— id: 48914, year: 2004, vol: 11, page: 61, stat: Journal Article,

Analysis of the intrinsic transcription termination mechanism and its control
Nudler, Evgeny; Gusarov, Ivan
2003 ;371(5):369-382, Methods in enzymology
— id: 46280, year: 2003, vol: 371, page: 369, stat: Journal Article,

Methods of walking with the RNA polymerase
Nudler, Evgeny; Gusarov, Ivan; Bar-Nahum, Gil
2003 ;371(5):160-169, Methods in enzymology
— id: 46282, year: 2003, vol: 371, page: 160, stat: Journal Article,

Control of intrinsic transcription termination by N and NusA: the basic mechanisms
Gusarov I; Nudler E
2001 Nov 16;107(4):437-449, Cell
Intrinsic transcription termination plays a crucial role in regulating gene expression in prokaryotes. After a short pause, the termination signal appears in RNA as a hairpin that destabilizes the elongation complex (EC). We demonstrate that negative and positive termination factors control the efficiency of termination primarily through a direct modulation of hairpin folding and, to a much lesser extent, by changing pausing at the point of termination. The mechanism controlling hairpin formation at the termination point relies on weak protein interactions with single-stranded RNA, which corresponds to the upstream portion of the hairpin. Escherichia coli NusA protein destabilizes these interactions and thus promotes hairpin folding and termination. Stabilization of these contacts by phage lambda N protein leads to antitermination
— id: 26542, year: 2001, vol: 107, page: 437, stat: Journal Article,

The mechanism of intrinsic transcription termination
Gusarov I; Nudler E
1999 Apr;3(4):495-504, Molecular cell
In bacteria, an intrinsic transcription termination signal appears in RNA as a hairpin followed by approximately eight uridines (U stretch) at the 3' terminus. This signal leads to rapid dissociation of the ternary elongation complex (TEC) into RNA, DNA, and an RNA polymerase. We demonstrate that the hairpin inactivates and then destabilizes TEC by weakening interactions in the RNA-DNA hybrid-binding site and the RNA-binding site that hold TEC together. Formation of the hairpin is restricted to the moment when TEC reaches the point of termination and depends upon melting of four to five hybrid base pairs that follow the hairpin's stem. The U stretch-induced pausing at the point of termination is crucial, providing additional time for hairpin formation. These results explain the mechanism of termination and aid in understanding of how cellular factors modulate this process
— id: 56433, year: 1999, vol: 3, page: 495, stat: Journal Article,

Spatial organization of transcription elongation complex in Escherichia coli
Nudler E; Gusarov I; Avetissova E; Kozlov M; Goldfarb A
1998 Jul 17;281(5375):424-428, Science
During RNA synthesis in the ternary elongation complex, RNA polymerase enzyme holds nucleic acids in three contiguous sites: the double-stranded DNA-binding site (DBS) ahead of the transcription bubble, the RNA-DNA heteroduplex-binding site (HBS), and the RNA-binding site (RBS) upstream of HBS. Photochemical cross-linking allowed mapping of the DNA and RNA contacts to specific positions on the amino acid sequence. Unexpectedly, the same protein regions were found to participate in both DBS and RBS. Thus, DNA entry and RNA exit occur close together in the RNA polymerase molecule, suggesting that the three sites constitute a single unit. The results explain how RNA in the integrated unit RBS-HBS-DBS may stabilize the ternary complex, whereas a hairpin in RNA result in its dissociation
— id: 7720, year: 1998, vol: 281, page: 424, stat: Journal Article,