101
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Degradation by stratum corneum proteases prevents endogenous RNase inhibitor from blocking antimicrobial activities of RNase 5 and RNase 7. J Invest Dermatol 2009; 129:2193-201. [PMID: 19262607 DOI: 10.1038/jid.2009.35] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The antimicrobial defense of the skin is partially mediated by RNase 7, an abundant ribonuclease of the stratum corneum (SC). Here, we investigated the expression and regulation of members of the RNase A family and of the endogenous RNase inhibitor (RI) protein in epidermal keratinocytes (KCs). Reverse transcription-PCR screening revealed that KCs expressed not only RNase 7 but also RNase 5, which was shown earlier to kill the yeast Candida albicans, as well as RNase 1, RNase 4, and RI. The mRNA and protein levels of RNase 5, RNase 7, and RI increased during KC differentiation. When RNase 5 and RNase 7 were incubated with RI in vitro, not only their ribonucleolytic activities but also their antimicrobial activities were strongly suppressed. Immunochemical analyses revealed that SC contains RNase 5, whereas RI was not detectable. Unlike recombinant RNase 5, recombinant RI was degraded when exposed to SC extract. The addition of aprotinin prevented the degradation of RI, indicating that serine proteases of the SC cleave RI. Taken together, this study adds RNase 5 to the list of antimicrobial factors present in the SC and suggests that proteases contribute indirectly to the defense function of the SC by releasing the RI-mediated inhibition of RNase 5 and RNase 7.
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102
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Turcotte RF, Raines RT. Design and characterization of an HIV-specific ribonuclease zymogen. AIDS Res Hum Retroviruses 2008; 24:1357-63. [PMID: 19025416 DOI: 10.1089/aid.2008.0146] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Ribonucleases are evoking medical interest because of their intrinsic cytotoxic activity. Most notably, ranpirnase, which is an amphibian ribonuclease, is in advanced clinical trials as a chemotherapeutic agent for the treatment of cancer. Here, we describe a strategy to create a novel antiviral agent based on bovine pancreatic ribonuclease (RNase A), a mammalian homologue of ranpirnase. Specifically, we have linked the N- and C-termini of RNase A with an amino acid sequence that is recognized and cleaved by human immunodeficiency virus (HIV) protease. This linkage obstructs the active site, forming an HIV-specific RNase A zymogen. Cleavage by HIV-1 protease increases ribonucleolytic activity by 50-fold. By relying on the proper function of HIV-1 protease, rather than its inhibition, our approach will not engender known mechanisms of resistance. Thus, we report an initial step toward a new class of agents for the treatment of HIV/AIDS.
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Affiliation(s)
- Rebecca F. Turcotte
- Medical Scientist Training Program and Biophysics Graduate Program, University of Wisconsin–Madison, Madison, Wisconsin 53706
| | - Ronald T. Raines
- Departments of Biochemistry and Chemistry, University of Wisconsin–Madison, Madison, Wisconsin 53706
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103
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Interaction of onconase with the human ribonuclease inhibitor protein. Biochem Biophys Res Commun 2008; 377:512-514. [PMID: 18930025 DOI: 10.1016/j.bbrc.2008.10.032] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2008] [Accepted: 10/02/2008] [Indexed: 11/21/2022]
Abstract
One of the tightest known protein-protein interactions in biology is that between members of the ribonuclease A superfamily and the ribonuclease inhibitor protein (RI). Some members of this superfamily are able to kill cancer cells, and the ability to evade RI is a major determinant of whether a ribonuclease will be cytotoxic. The archetypal cytotoxic ribonuclease, onconase (ONC), is in late-stage clinical trials for the treatment of malignant mesothelioma. We present here the first measurement of the inhibition of the ribonucleolytic activity of ONC by RI. This inhibition occurs with K(i)=0.15muM in a solution of low salt concentration.
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104
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Torrent G, Benito A, Castro J, Ribó M, Vilanova M. Contribution of the C30/C75 disulfide bond to the biological properties of onconase. Biol Chem 2008. [DOI: 10.1515/bc.2008.114_bchm.just-accepted] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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105
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Torrent G, Benito A, Castro J, Ribó M, Vilanova M. Contribution of the C30/C75 disulfide bond to the biological properties of onconase. Biol Chem 2008; 389:1127-36. [DOI: 10.1515/bc.2008.114] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
AbstractOnconase, a member of the pancreatic type ribonuclease family, is currently used as a chemotherapeutic agent for the treatment of different types of cancer. It is widely accepted that one of the properties that renders this enzyme cytotoxic is its ability to evade the cytosolic ribonuclease inhibitor (RI). In the present work, we produced and characterized an onconase variant that lacks the disulfide bond C30/C75. This variant mimics the stable unfolding intermediate des(30–75) produced in the reductive unfolding pathway of onconase. We found that the reduction of the C30/C75 disulfide bond does not significantly alter the cytotoxic properties of onconase, although the variant possesses a notably reduced conformational stability. Interestingly, both its catalytic activity and its ability to evade RI are comparable to wild-type onconase under mild reductive conditions in which the three disulfide containing intermediate des(30–75) is present. These results suggest that the C30/C75 disulfide bond could easily be reduced under physiological redox conditions.
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106
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Abstract
As our understanding of the molecular mechanisms driving complex biological processes grows, the role of chemical biology will continue to expand. The 2008 American Society for Biochemistry and Molecular Biology meeting showcased recent progress in the field of chemical biology while simultaneously pointing toward the future of research at the interface between chemistry and biology.
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Affiliation(s)
- Robert H Newman
- Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, Maryland 21205, USA
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107
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Edelweiss E, Balandin TG, Ivanova JL, Lutsenko GV, Leonova OG, Popenko VI, Sapozhnikov AM, Deyev SM. Barnase as a new therapeutic agent triggering apoptosis in human cancer cells. PLoS One 2008; 3:e2434. [PMID: 18560598 PMCID: PMC2413406 DOI: 10.1371/journal.pone.0002434] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2007] [Accepted: 05/13/2008] [Indexed: 02/05/2023] Open
Abstract
Background RNases are currently studied as non-mutagenic alternatives to the harmful DNA-damaging anticancer drugs commonly used in clinical practice. Many mammalian RNases are not potent toxins due to the strong inhibition by ribonuclease inhibitor (RI) presented in the cytoplasm of mammalian cells. Methodology/Principal Findings In search of new effective anticancer RNases we studied the effects of barnase, a ribonuclease from Bacillus amyloliquefaciens, on human cancer cells. We found that barnase is resistant to RI. In MTT cell viability assay, barnase was cytotoxic to human carcinoma cell lines with half-inhibitory concentrations (IC50) ranging from 0.2 to 13 µM and to leukemia cell lines with IC50 values ranging from 2.4 to 82 µM. Also, we characterized the cytotoxic effects of barnase-based immunoRNase scFv 4D5-dibarnase, which consists of two barnase molecules serially fused to the single-chain variable fragment (scFv) of humanized antibody 4D5 that recognizes the extracellular domain of cancer marker HER2. The scFv 4D5-dibarnase specifically bound to HER2-positive cells and was internalized via receptor-mediated endocytosis. The intracellular localization of internalized scFv 4D5-dibarnase was determined by electronic microscopy. The cytotoxic effect of scFv 4D5-dibarnase on HER2-positive human ovarian carcinoma SKOV-3 cells (IC50 = 1.8 nM) was three orders of magnitude greater than that of barnase alone. Both barnase and scFv 4D5-dibarnase induced apoptosis in SKOV-3 cells accompanied by internucleosomal chromatin fragmentation, membrane blebbing, the appearance of phosphatidylserine on the outer leaflet of the plasma membrane, and the activation of caspase-3. Conclusions/Significance These results demonstrate that barnase is a potent toxic agent for targeting to cancer cells.
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Affiliation(s)
- Evelina Edelweiss
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, Russia
- * E-mail: (EE); (SMD)
| | - Taras G. Balandin
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, Russia
| | - Julia L. Ivanova
- Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, Moscow, Russia
| | - Gennady V. Lutsenko
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, Russia
| | - Olga G. Leonova
- Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, Moscow, Russia
| | - Vladimir I. Popenko
- Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, Moscow, Russia
| | - Alexander M. Sapozhnikov
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, Russia
| | - Sergey M. Deyev
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, Russia
- Institute of Gene Biology, Russian Academy of Sciences, Moscow, Russia
- * E-mail: (EE); (SMD)
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108
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Abstract
Ranpirnase, a cytotoxic ribonuclease from the frog Rana pipiens, is the archetype of a novel class of cancer chemotherapeutic agents based on homologs and variants of bovine pancreatic ribonuclease (RNase A). Ranpirnase in combination with doxorubicin is in clinical trials for the treatment of unresectable malignant mesothelioma and other cancers. The putative mechanism for ranpirnase-mediated cytotoxicity involves binding to anionic components of the extracellular membrane, cytosolic internalization, and degradation of transfer RNA leading to apoptosis. The maintenance of ribonucleolytic activity in the presence of the cytosolic ribonuclease inhibitor protein is a key aspect of the cytotoxic activity of ranpirnase. The basis for its specific toxicity for cancer cells is not known. This review describes the development of ranpirnase as a cancer chemotherapeutic agent.
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Affiliation(s)
- J Eugene Lee
- Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706-1544, USA
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109
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Rutkoski TJ, Raines RT. Evasion of ribonuclease inhibitor as a determinant of ribonuclease cytotoxicity. Curr Pharm Biotechnol 2008; 9:185-9. [PMID: 18673284 PMCID: PMC2818677 DOI: 10.2174/138920108784567344] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Onconase (ONC) is an amphibian member of the bovine pancreatic ribonuclease (RNase A) superfamily that exhibits innate antitumoral activity. ONC has been granted both orphan-drug and fast-track status by the U.S. Food and Drug Administration for the treatment of malignant mesothelioma, and is poised to become the first chemotherapeutic agent based on a ribonuclease. Investigations into the mechanism of ribonuclease-based cytotoxicity have elucidated several important determinants for cytotoxicity, including efficient deliverance of ribonucleolytic activity to the cytosol and preservation of conformation stability. Nevertheless, the most striking similarity between ONC and bovine seminal ribonuclease, another naturally cytotoxic ribonuclease, is their insensitivity to inhibition by the potent cytosolic ribonuclease inhibitor protein (RI). RI typically binds to its ribonuclease ligands with femtomolar affinity--an extraordinary feat considering the modest sequence identity among the bound ribonucleases. Mammalian ribonucleases such as RNase A or its human homologue, RNase 1, have the potential to be more attractive chemotherapeutic agents than ONC owing to their higher catalytic activity, low potential for immunogenicity, favorable tissue distribution, and high therapeutic index, but are limited by their sensitivity to RI. These non-toxic mammalian ribonucleases can be transformed into potent cytotoxins by engendering them with RI-evasion using protein engineering strategies such as site-directed mutagenesis, multimerization, fusion to a targeting moiety, and chemical modification. In several instances, these engineered ribonucleases exhibit greater cytotoxicity in vitro than does ONC. Herein, we review the biochemical characteristics of RIribonuclease complexes and progress towards the development of mammalian ribonuclease-based chemotherapeutics through the elicitation of RI-evasion.
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Affiliation(s)
| | - Ronald T. Raines
- Address correspondence to this author at the Department of Biochemistry, University of Wisconsin–Madison, 433 Babcock Drive, Madison, WI 53706-1544, USA; Tel: (608) 262-8588; Fax: (608) 262-3453;
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110
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Ardelt W, Shogen K, Darzynkiewicz Z. Onconase and amphinase, the antitumor ribonucleases from Rana pipiens oocytes. Curr Pharm Biotechnol 2008; 9:215-25. [PMID: 18673287 PMCID: PMC2586917 DOI: 10.2174/138920108784567245] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Rana pipiens oocytes contain two homologues of pancreatic ribonuclease A that are cytostatic and cytotoxic to human cancer cells. Extensively studied Onconase is in advanced Phase IIIb clinical trials against malignant mesothelioma, while Amphinase is a novel enzyme in pre-clinical development. Onconase is the smallest (104 amino acid residues) member of the ribonuclease A superfamily while Amphinase (114 residues) is the largest among amphibian ribonucleases. Both enzymes share the characteristic frog ribonucleases C-terminal disulfide bond but another signature of this group, the N-terminal pyroglutamate, an integral part of Onconase active site is not conserved in Amphinase. Although Onconase and Amphinase are weak catalysts their enzymatic activities are required for cytostatic and cytotoxic activity. While it was postulated that tRNA is the primary substrate of Onconase in vivo there is also extensive indirect evidence that suggests other RNA species, in particular micro RNAs, may actually be the critical target of these ribonucleases. The cytostatic effects of Onconase and Amphinase are manifested as cell arrest in the G(1) cell cycle phase. Apoptosis then follows involving activation of endonucleases(s), caspases, serine proteases and transglutaminase. Onconase was shown to be strongly synergistic when combined with numerous other antitumor modalities. Onconase and Amphinase are highly cationic molecules and their preferential toxicity towards cancer cells (having distinctly higher negative charge compared to normal cells) may depend on increased binding efficiency to the cell surface by electrostatic interactions.
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Affiliation(s)
- W Ardelt
- Alfacell Corporation, 300 Atrium Drive, Somerset, NJ 08873, USA.
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111
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Kövér KE, Bruix M, Santoro J, Batta G, Laurents DV, Rico M. The solution structure and dynamics of human pancreatic ribonuclease determined by NMR spectroscopy provide insight into its remarkable biological activities and inhibition. J Mol Biol 2008; 379:953-65. [PMID: 18495155 DOI: 10.1016/j.jmb.2008.04.042] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2008] [Revised: 04/08/2008] [Accepted: 04/14/2008] [Indexed: 02/05/2023]
Abstract
Human pancreatic ribonuclease (RNase 1) is expressed in many tissues; has several important enzymatic and biological activities, including efficient cleavage of single-stranded RNA, double-stranded RNA and double-stranded RNA-DNA hybrids, digestion of dietary RNA, regulation of vascular homeostasis, inactivation of the HIV, activation of immature dendritic cells and induction of cytokine production; and furthermore shows potential as an anti-tumor agent. The solution structure and dynamics of uncomplexed, wild-type RNase 1 have been determined by NMR spectroscopy methods to better understand these activities. The family of 20 structures determined on the basis of 6115 unambiguous nuclear Overhauser enhancements is well resolved (pairwise backbone RMSD=1.07 A) and has the classic RNase A type of tertiary structure. Important structural differences compared with previously determined crystal structures of RNase 1 variants or inhibitor-bound complexes are observed in the conformation of loop regions and side chains implicated in the enzymatic as well as biological activities and binding to the cytoplasmic RNase inhibitor. Multiple side chain conformations observed for key surface residues are proposed to be crucial for membrane binding as well as translocation and efficient RNA hydrolysis. (15)N-(1)H relaxation measurements interpreted with the standard and our extended Lipari-Szabo formalism reveal rigid regions and identify more dynamic loop regions. Some of the most dynamic areas are key for binding to the cytoplasmic RNase inhibitor. This finding and the important differences observed between the structure in solution and that bound to the inhibitor are indications that RNase 1 to inhibitor binding can be better described by the "induced fit" model rather than the rigid "lock-into-key" mechanism. Translational diffusion measurements reveal that RNase 1 is predominantly dimeric above 1 mM concentration; the possible implications of this dimeric state for the remarkable biological properties of RNase 1 are discussed.
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Affiliation(s)
- K E Kövér
- Department of Chemistry, University of Debrecen, 4010 Debrecen, Hungary
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112
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113
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Rodríguez M, Moussaoui M, Benito A, Cuchillo CM, Nogués MV, Vilanova M. Human pancreatic ribonuclease presents higher endonucleolytic activity than ribonuclease A. Arch Biochem Biophys 2008; 471:191-7. [PMID: 18191631 DOI: 10.1016/j.abb.2007.12.016] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2007] [Revised: 12/14/2007] [Accepted: 12/15/2007] [Indexed: 11/17/2022]
Abstract
Analyzing the pattern of oligonucleotide formation induced by HP-RNase cleavage shows that the enzyme does not act randomly and follows a more endonucleolytic pattern when compared to RNase A. The enzyme prefers the binding and cleavage of longer substrate molecules, especially when the phosphodiester bond that is broken is 8-11 nucleotides away from at least one of the ends of the substrate molecule. This more endonucleolytic pattern is more appropriate for an enzyme with a regulatory role. Deleting two positive charges on the N-terminus (Arg4 and Lys6) modifies this pattern of external/internal phosphodiester bond cleavage preference, and produces a more exonucleolytic enzyme. These residues may reinforce the strength of a non-catalytic secondary phosphate binding (p2) or, alternatively, constitute a new non-catalytic phosphate binding subsite (p3).
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Affiliation(s)
- M Rodríguez
- Laboratori d'Enginyeria de Proteïnes, Departament de Biologia, Facultat de Ciències, Universitat de Girona, Campus de Montilivi s/n, 17071 Girona, Spain
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114
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Zhou HX, Qin S, Tjong H. Modeling Protein–Protein and Protein–Nucleic Acid Interactions: Structure, Thermodynamics, and Kinetics. ANNUAL REPORTS IN COMPUTATIONAL CHEMISTRY 2008. [DOI: 10.1016/s1574-1400(08)00004-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
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115
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Johnson RJ, Lavis LD, Raines RT. Intraspecies regulation of ribonucleolytic activity. Biochemistry 2007; 46:13131-40. [PMID: 17956129 DOI: 10.1021/bi701521q] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The evolutionary rate of proteins involved in obligate protein-protein interactions is slower and the degree of coevolution higher than that for nonobligate protein-protein interactions. The coevolution of the proteins involved in certain nonobligate interactions is, however, essential to cell survival. To gain insight into the coevolution of one such nonobligate protein pair, the cytosolic ribonuclease inhibitor (RI) proteins and secretory pancreatic-type ribonucleases from cow (Bos taurus) and human (Homo sapiens) were produced in Escherichia coli and purified, and their physicochemical properties were analyzed. The two intraspecies complexes were found to be extremely tight (bovine Kd = 0.69 fM; human Kd = 0.34 fM). Human RI binds to its cognate ribonuclease (RNase 1) with 100-fold greater affinity than to the bovine homologue (RNase A). In contrast, bovine RI binds to RNase 1 and RNase A with nearly equal affinity. This broader specificity is consistent with there being more pancreatic-type ribonucleases in cows (20) than humans (13). Human RI (32 cysteine residues) also has 4-fold less resistance to oxidation by hydrogen peroxide than does bovine RI (29 cysteine residues). This decreased oxidative stability of human RI, which is caused largely by Cys74, implies a larger role for human RI as an antioxidant. The conformational and oxidative stabilities of both RIs increase upon complex formation with ribonucleases. Thus, RI has evolved to maintain its inhibition of invading ribonucleases, even when confronted with extreme environmental stress. That role appears to take precedence over its role in mediating oxidative damage.
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Affiliation(s)
- R Jeremy Johnson
- Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706-1544, USA
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116
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Lee JE, Bae E, Bingman CA, Phillips GN, Raines RT. Structural basis for catalysis by onconase. J Mol Biol 2007; 375:165-77. [PMID: 18001769 DOI: 10.1016/j.jmb.2007.09.089] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2007] [Accepted: 09/20/2007] [Indexed: 11/18/2022]
Abstract
Onconase (ONC) is a homolog of bovine pancreatic ribonuclease (RNase A) from the frog Rana pipiens. ONC displays antitumoral activity and is in advanced clinical trials for the treatment of cancer. Here, we report the first atomic structures of ONC-nucleic acid complexes: a T89N/E91A ONC-5'-AMP complex at 1.65 A resolution and a wild-type ONC-d(AUGA) complex at 1.90 A resolution. The latter structure and site-directed mutagenesis were used to reveal the atomic basis for substrate recognition and turnover by ONC. The residues in ONC that are proximal to the scissile phosphodiester bond (His10, Lys31, and His97) and uracil nucleobase (Thr35, Asp67, and Phe98) are conserved from RNase A and serve to generate a similar bell-shaped pH versus k(cat)/K(M) profile for RNA cleavage. Glu91 of ONC forms two hydrogen bonds with the guanine nucleobase in d(AUGA), and Thr89 is in close proximity to that nucleobase. Installing a neutral or cationic residue at position 91 or an asparagine residue at position 89 virtually eliminated the 10(2)-fold guanine:adenine preference of ONC. A variant that combined such substitutions, T89N/E91A ONC, actually preferred adenine over guanine. In contrast, installing an arginine residue at position 91 increased the guanine preference and afforded an ONC variant with the highest known k(cat)/K(M) value. These data indicate that ONC discriminates between guanine and adenine by using Coulombic interactions and a network of hydrogen bonds. The structure of the ONC-d(AUGA) complex was also used to probe other aspects of catalysis. For example, the T5R substitution, designed to create a favorable Coulombic interaction between ONC and a phosphoryl group in RNA, increased ribonucleolytic activity by twofold. No variant, however, was more toxic to human cancer cells than wild-type ONC. Together, these findings provide a cynosure for understanding catalysis of RNA cleavage in a system of high medicinal relevance.
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Affiliation(s)
- J Eugene Lee
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706-1544, USA
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117
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Phillips GN, Fox BG, Markley JL, Volkman BF, Bae E, Bitto E, Bingman CA, Frederick RO, McCoy JG, Lytle BL, Pierce BS, Song J, Twigger SN. Structures of proteins of biomedical interest from the Center for Eukaryotic Structural Genomics. ACTA ACUST UNITED AC 2007; 8:73-84. [PMID: 17786587 DOI: 10.1007/s10969-007-9023-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2007] [Accepted: 07/17/2007] [Indexed: 12/01/2022]
Abstract
The Center for Eukaryotic Structural Genomics (CESG) produces and solves the structures of proteins from eukaryotes. We have developed and operate a pipeline to both solve structures and to test new methodologies. Both NMR and X-ray crystallography methods are used for structure solution. CESG chooses targets based on sequence dissimilarity to known structures, medical relevance, and nominations from members of the scientific community. Many times proteins qualify in more than one of these categories. Here we review some of the structures that have connections to human health and disease.
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Affiliation(s)
- George N Phillips
- Center for Eukaryotic Structural Genomics, Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706, USA.
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118
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Johnson RJ, Chao TY, Lavis LD, Raines RT. Cytotoxic ribonucleases: the dichotomy of Coulombic forces. Biochemistry 2007; 46:10308-16. [PMID: 17705507 PMCID: PMC2864629 DOI: 10.1021/bi700857u] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Cells tightly regulate their contents. Still, nonspecific Coulombic interactions between cationic molecules and anionic membrane components can lead to adventitious endocytosis. Here, we characterize this process in a natural system. To do so, we create variants of human pancreatic ribonuclease (RNase 1) that differ in net molecular charge. By conjugating a small-molecule latent fluorophore to these variants and using flow cytometry, we are able to determine the kinetic mechanism for RNase 1 internalization into live human cells. We find that internalization increases with solution concentration and is not saturable. Internalization also increases with time to a steady-state level, which varies linearly with molecular charge. In contrast, the rate constant for internalization (t1/2 = 2 h) is independent of charge. We conclude that internalization involves an extracellular equilibrium complex between the cationic proteins and abundant anionic cell-surface molecules, followed by rate-limiting internalization. The enhanced internalization of more cationic variants of RNase 1 is, however, countered by their increased affinity for the cytosolic ribonuclease inhibitor protein, which is anionic. Thus, Coulombic forces mediate extracellular and intracellular equilibria in a dichotomous manner that both endangers cells and defends them from the potentially lethal enzymatic activity of ribonucleases.
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Affiliation(s)
- R. Jeremy Johnson
- Department of Biochemistry, University of Wisconsin–Madison, Madison, Wisconsin 53706
| | - Tzu-Yuan Chao
- Department of Biochemistry, University of Wisconsin–Madison, Madison, Wisconsin 53706
| | - Luke D. Lavis
- Department of Chemistry, University of Wisconsin–Madison, Madison, Wisconsin 53706
| | - Ronald T. Raines
- Department of Biochemistry, University of Wisconsin–Madison, Madison, Wisconsin 53706
- Department of Chemistry, University of Wisconsin–Madison, Madison, Wisconsin 53706
- To whom correspondence should be addressed: Department of Biochemistry, University of Wisconsin–Madison, 433 Babcock Drive, Madison, WI 53706-1544. Telephone: 608-262-8588. Fax: 608-262-3453.
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