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1.  Thermodynamics of Coupled Folding in the Interaction of Archaeal RNase P Proteins RPP21 and RPP29 
Biochemistry  2012;51(4):926-935.
We have used isothermal titration calorimetry (ITC) to identify and describe binding-coupled equilibria in the interaction between two protein subunits of archaeal ribonuclease P (RNase P). In all three domains of life, RNase P is a ribonucleoprotein complex that is primarily responsible for catalyzing the Mg2+-dependent cleavage of the 5′ leader sequence of precursor tRNAs during tRNA maturation. In archaea, RNase P has been shown to be composed of one catalytic RNA and up to five proteins, four of which associate in the absence of RNA as two functional heterodimers, POP5-RPP30 and RPP21-RPP29. NMR studies of the Pyrococcus furiosus RPP21 and RPP29 proteins in their free and complexed states provided evidence for significant protein folding upon binding. ITC experiments were performed over a range of temperatures, ionic strengths, pH values and in buffers with varying ionization potential, and with a folding-deficient RPP21 point mutant. These experiments revealed a negative heat capacity change (ΔCp), nearly twice that predicted from surface accessibility calculations, a strong salt dependence to the interaction and proton release at neutral pH, but a small net contribution from these to the excess ΔCp. We considered potential contributions from protein folding and burial of interfacial water molecules based on structural and spectroscopic data. We conclude that binding-coupled protein folding is likely responsible for a significant portion of the excess ΔCp. These findings provide novel structural-thermodynamic insights into coupled equilibria that enable specificity in macromolecular assemblies.
doi:10.1021/bi201674d
PMCID: PMC3964601  PMID: 22243443
2.  Use of Proteomic Analysis To Elucidate the Role of Calcium in Acetone-Butanol-Ethanol Fermentation by Clostridium beijerinckii NCIMB 8052 
Calcium carbonate increases growth, substrate utilization, and acetone-butanol-ethanol (ABE) fermentation by Clostridium beijerinckii NCIMB 8052. Toward an understanding of the basis for these pleiotropic effects, we profiled changes in the C. beijerinckii NCIMB 8052 proteome that occur in response to the addition of CaCO3. We observed increases in the levels of different heat shock proteins (GrpE and DnaK), sugar transporters, and proteins involved in DNA synthesis, repair, recombination, and replication. We also noted significant decreases in the levels of proteins involved in metabolism, nucleic acid stabilization, sporulation, oxidative and antibiotic stress responses, and signal transduction. We determined that CaCO3 enhances ABE fermentation due to both its buffering effects and its ability to influence key cellular processes, such as sugar transport, butanol tolerance, and solventogenesis. Moreover, activity assays in vitro for select solventogenic enzymes revealed that part of the underpinning for the CaCO3-mediated increase in the level of ABE fermentation stems from the enhanced activity of these catalysts in the presence of Ca2+. Collectively, these proteomic and biochemical studies provide new insights into the multifactorial basis for the stimulation of ABE fermentation and butanol tolerance in the presence of CaCO3.
doi:10.1128/AEM.02969-12
PMCID: PMC3536099  PMID: 23104411
3.  Complete Genome Sequence of Desulfurococcus fermentans, a Hyperthermophilic Cellulolytic Crenarchaeon Isolated from a Freshwater Hot Spring in Kamchatka, Russia 
Journal of Bacteriology  2012;194(20):5703-5704.
Desulfurococcus fermentans is the first known cellulolytic archaeon. This hyperthermophilic and strictly anaerobic crenarchaeon produces hydrogen from fermentation of various carbohydrates and peptides without inhibition by accumulating hydrogen. The complete genome sequence reported here suggested that D. fermentans employs membrane-bound hydrogenases and novel glycohydrolases for hydrogen production from cellulose.
doi:10.1128/JB.01314-12
PMCID: PMC3458677  PMID: 23012283
4.  Cooperative RNP assembly: Complementary rescue of structural defects by protein and RNA subunits of archaeal RNase P 
Journal of molecular biology  2011;411(2):368-383.
RNase P is a ribonucleoprotein (RNP) complex that utilizes a Mg2+-dependent RNA catalyst to cleave the 5′-leader of precursor tRNAs (pre-tRNAs) and generate mature tRNAs. The bacterial RNase P protein (RPP) aids RNase P RNA (RPR) catalysis by promoting substrate binding, Mg2+ coordination, and product release. Archaeal RNase P comprises an RPR and at least four RPPs, which have eukaryal homologs and function as two binary complexes (POP5•RPP30 and RPP21•RPP29). In this study, we employed a previously characterized substrate-enzyme conjugate [pre-tRNATyr-Methanocaldococcus jannaschii (Mja) RPR] to investigate the functional role of a universally conserved uridine in a bulge-helix structure in archaeal RPRs. Deletion of this bulged uridine resulted in an 80-fold decrease in the self-cleavage rate of pre-tRNATyr-MjaΔU RPR compared to the wildtype, and this defect was partially ameliorated upon addition of either RPP pair. The catalytic defect in the archaeal mutant RPR mirrors that reported in a bacterial RPR and highlights a parallel in their active sites. Furthermore, an N-terminal deletion mutant of Pyrococcus furiosus (Pfu) RPP29 that is defective in assembling with its binary partner RPP21, as assessed by isothermal titration calorimetry and NMR spectroscopy, is functional when reconstituted with the cognate Pfu RPR. Collectively, these results indicate that archaeal RPPs are able to compensate for structural defects in their cognate RPR and vice-versa, and provide striking examples of the cooperative subunit interactions critical for driving archaeal RNase P towards its functional conformation. (236 words)
doi:10.1016/j.jmb.2011.05.012
PMCID: PMC3143260  PMID: 21683084
pre-tRNA processing; in vitro reconstitution; mutational rescue
5.  Evidence for recycling of external guide sequences during cleavage of bipartite substrates in vitro by reconstituted archaeal RNase P 
Journal of molecular biology  2010;405(5):1121-1127.
RNA-mediated RNA cleavage events are being increasingly exploited to disrupt RNA function, an important objective in post-genomic biology. RNase P, a ribonucleoprotein enzyme, which catalyzes the removal of 5′-leaders from precursor tRNAs (pre-tRNAs), has previously been utilized for targeted degradation of cellular RNAs. In one of these strategies, borne out in bacterial and mammalian cell culture, an external guide sequence (EGS) RNA when base-paired to a target RNA makes the latter a substrate for endogenous RNase P by rendering the bipartite substrate-EGS complex a pre-tRNA structural mimic. In this study, we first obtained evidence that four different mesophilic and thermophilic archaeal RNase P holoenzymes, reconstituted in vitro using their respective constituent RNA and protein subunits, recognize and cleave such substrate-EGS complexes. We further demonstrate that these EGSs engage in multiple rounds of substrate recognition while assisting archaeal RNase P-mediated cleavage of a target RNA in vitro. Taken together, the EGS-based approach merits consideration as a gene knock-down tool in archaea.
doi:10.1016/j.jmb.2010.11.056
PMCID: PMC3025773  PMID: 21144851
Targeted RNA degradation; turnover
6.  Fidelity of tRNA 5′-maturation: a possible basis for the functional dependence of archaeal and eukaryal RNase P on multiple protein cofactors 
Nucleic Acids Research  2012;40(10):4666-4680.
RNase P, which catalyzes tRNA 5′-maturation, typically comprises a catalytic RNase P RNA (RPR) and a varying number of RNase P proteins (RPPs): 1 in bacteria, at least 4 in archaea and 9 in eukarya. The four archaeal RPPs have eukaryotic homologs and function as heterodimers (POP5•RPP30 and RPP21•RPP29). By studying the archaeal Methanocaldococcus jannaschii RPR's cis cleavage of precursor tRNAGln (pre-tRNAGln), which lacks certain consensus structures/sequences needed for substrate recognition, we demonstrate that RPP21•RPP29 and POP5•RPP30 can rescue the RPR's mis-cleavage tendency independently by 4-fold and together by 25-fold, suggesting that they operate by distinct mechanisms. This synergistic and preferential shift toward correct cleavage results from the ability of archaeal RPPs to selectively increase the RPR's apparent rate of correct cleavage by 11 140-fold, compared to only 480-fold for mis-cleavage. Moreover, POP5•RPP30, like the bacterial RPP, helps normalize the RPR's rates of cleavage of non-consensus and consensus pre-tRNAs. We also show that archaeal and eukaryal RNase P, compared to their bacterial relatives, exhibit higher fidelity of 5′-maturation of pre-tRNAGln and some of its mutant derivatives. Our results suggest that protein-rich RNase P variants might have evolved to support flexibility in substrate recognition while catalyzing efficient, high-fidelity 5′-processing.
doi:10.1093/nar/gks013
PMCID: PMC3378863  PMID: 22298511
7.  Assembly of the Complex between Archaeal RNase P Proteins RPP30 and Pop5 
Archaea  2011;2011:891531.
RNase P is a highly conserved ribonucleoprotein enzyme that represents a model complex for understanding macromolecular RNA-protein interactions. Archaeal RNase P consists of one RNA and up to five proteins (Pop5, RPP30, RPP21, RPP29, and RPP38/L7Ae). Four of these proteins function in pairs (Pop5-RPP30 and RPP21–RPP29). We have used nuclear magnetic resonance (NMR) spectroscopy and isothermal titration calorimetry (ITC) to characterize the interaction between Pop5 and RPP30 from the hyperthermophilic archaeon Pyrococcus furiosus (Pfu). NMR backbone resonance assignments of free RPP30 (25 kDa) indicate that the protein is well structured in solution, with a secondary structure matching that observed in a closely related crystal structure. Chemical shift perturbations upon the addition of Pop5 (14 kDa) reveal its binding surface on RPP30. ITC experiments confirm a net 1 : 1 stoichiometry for this tight protein-protein interaction and exhibit complex isotherms, indicative of higher-order binding. Indeed, light scattering and size exclusion chromatography data reveal the complex to exist as a 78 kDa heterotetramer with two copies each of Pop5 and RPP30. These results will inform future efforts to elucidate the functional role of the Pop5-RPP30 complex in RNase P assembly and catalysis.
doi:10.1155/2011/891531
PMCID: PMC3227427  PMID: 22162665
8.  Unexpected diversity of RNase P, an ancient tRNA processing enzyme: challenges and prospects 
FEBS letters  2010;584(2):287-296.
For an enzyme functioning predominantly in a seemingly housekeeping role of 5′ tRNA maturation, RNase P displays a remarkable diversity in subunit make-up across the three domains of life. Despite the protein complexity of this ribonucleoprotein enzyme increasing dramatically from bacteria to eukarya, the catalytic function rests with the RNA subunit during evolution. However, the recent demonstration of a protein-only human mitochondrial RNase P has added further intrigue to the compositional variability of this enzyme. In this review, we discuss some possible reasons underlying the structural diversity of the active sites, and use them as thematic bases for elaborating new directions to understand how functional variations might have contributed to the complex evolution of RNase P.
doi:10.1016/j.febslet.2009.11.048
PMCID: PMC2799185  PMID: 19931535
RNase P; precursor tRNA; diversity; evolution; organellar
9.  Solution Structure of an Archaeal RNase P Binary Protein Complex. Formation of the 30-kDa Complex Between Pyrococcus furiosus RPP21 and RPP29 is Accompanied by Coupled Protein Folding, and Highlights Critical Features for Protein-Protein and Protein-RNA Interactions 
Journal of molecular biology  2009;393(5):1043-1055.
RNase P is a ribonucleoprotein (RNP) enzyme that catalyzes the Mg2+-dependent 5’ maturation of precursor tRNAs. In all domains of life, it is a ribozyme: the RNase P RNA (RPR) component has been demonstrated to be responsible for catalysis. However, the number of RNase P protein subunits (RPPs) varies from one in bacteria to nine or ten in eukarya. The archaeal RPR is associated with at least four RPPs, which function in pairs (RPP21–RPP29 and RPP30-POP5). We used solution NMR spectroscopy to determine the three-dimensional structure of the protein-protein complex comprising Pyrococcus furiosus (Pfu) RPP21 and RPP29. We found that the protein-protein interaction is characterized by coupled folding of secondary structural elements that participate in interface formation. In addition to detailing the intermolecular contacts that stabilize this 30-kDa binary complex, the structure identifies surfaces rich in conserved basic residues likely vital for recognition of the RPR and/or precursor tRNA. Furthermore, enzymatic footprinting experiments allowed us to localize the RPP21–RPP29 complex to the specificity domain of the RPR. These findings provide valuable new insights into mechanisms of RNP assembly and serve as important steps towards a three-dimensional model of this ancient RNP enzyme.
doi:10.1016/j.jmb.2009.08.068
PMCID: PMC2782587  PMID: 19733182
10.  Cleavage of model substrates by archaeal RNase P: role of protein cofactors in cleavage-site selection 
Nucleic Acids Research  2010;39(3):1105-1116.
RNase P is a catalytic ribonucleoprotein primarily involved in tRNA biogenesis. Archaeal RNase P comprises a catalytic RNase P RNA (RPR) and at least four protein cofactors (RPPs), which function as two binary complexes (POP5•RPP30 and RPP21• RPP29). Exploiting the ability to assemble a functional Pyrococcus furiosus (Pfu) RNase P in vitro, we examined the role of RPPs in influencing substrate recognition by the RPR. We first demonstrate that Pfu RPR, like its bacterial and eukaryal counterparts, cleaves model hairpin loop substrates albeit at rates 90- to 200-fold lower when compared with cleavage by bacterial RPR, highlighting the functionally comparable catalytic cores in bacterial and archaeal RPRs. By investigating cleavage-site selection exhibited by Pfu RPR (±RPPs) with various model substrates missing consensus-recognition elements, we determined substrate features whose recognition is facilitated by either POP5•RPP30 or RPP21•RPP29 (directly or indirectly via the RPR). Our results also revealed that Pfu RPR + RPP21•RPP29 displays substrate-recognition properties coinciding with those of the bacterial RPR-alone reaction rather than the Pfu RPR, and that this behaviour is attributable to structural differences in the substrate-specificity domains of bacterial and archaeal RPRs. Moreover, our data reveal a hierarchy in recognition elements that dictates cleavage-site selection by archaeal RNase P.
doi:10.1093/nar/gkq732
PMCID: PMC3035440  PMID: 20935047
11.  Archaeal/Eukaryal RNase P: subunits, functions and RNA diversification 
Nucleic Acids Research  2010;38(22):7885-7894.
RNase P, a catalytic ribonucleoprotein (RNP), is best known for its role in precursor tRNA processing. Recent discoveries have revealed that eukaryal RNase P is also required for transcription and processing of select non-coding RNAs, thus enmeshing RNase P in an intricate network of machineries required for gene expression. Moreover, the RNase P RNA seems to have been subject to gene duplication, selection and divergence to generate two new catalytic RNPs, RNase MRP and MRP-TERT, which perform novel functions encompassing cell cycle control and stem cell biology. We present new evidence and perspectives on the functional diversification of the RNase P RNA to highlight it as a paradigm for the evolutionary plasticity that underlies the extant broad repertoire of catalytic and unexpected regulatory roles played by RNA-driven RNPs.
doi:10.1093/nar/gkq701
PMCID: PMC3001073  PMID: 20716516
12.  Dissecting functional cooperation among protein subunits in archaeal RNase P, a catalytic ribonucleoprotein complex 
Nucleic Acids Research  2010;38(22):8316-8327.
RNase P catalyzes the Mg2+-dependent 5′-maturation of precursor tRNAs. Biochemical studies on the bacterial holoenzyme, composed of one catalytic RNase P RNA (RPR) and one RNase P protein (RPP), have helped understand the pleiotropic roles (including substrate/Mg2+ binding) by which a protein could facilitate RNA catalysis. As a model for uncovering the functional coordination among multiple proteins that aid an RNA catalyst, we use archaeal RNase P, which comprises one catalytic RPR and at least four RPPs. Exploiting our previous finding that these archaeal RPPs function as two binary RPP complexes (POP5•RPP30 and RPP21•RPP29), we prepared recombinant RPP pairs from three archaea and established interchangeability of subunits through homologous/heterologous assemblies. Our finding that archaeal POP5•RPP30 reconstituted with bacterial and organellar RPRs suggests functional overlap of this binary complex with the bacterial RPP and highlights their shared recognition of a phylogenetically-conserved RPR catalytic core, whose minimal attributes we further defined through deletion mutagenesis. Moreover, single-turnover kinetic studies revealed that while POP5•RPP30 is solely responsible for enhancing the RPR’s rate of precursor tRNA cleavage (by 60-fold), RPP21•RPP29 contributes to increased substrate affinity (by 16-fold). Collectively, these studies provide new perspectives on the functioning and evolution of an ancient, catalytic ribonucleoprotein.
doi:10.1093/nar/gkq668
PMCID: PMC3001054  PMID: 20705647
13.  Studies on Methanocaldococcus jannaschii RNase P reveal insights into the roles of RNA and protein cofactors in RNase P catalysis 
Nucleic Acids Research  2008;36(12):4172-4180.
Ribonuclease P (RNase P), a ribonucleoprotein (RNP) complex required for tRNA maturation, comprises one essential RNA (RPR) and protein subunits (RPPs) numbering one in bacteria, and at least four in archaea and nine in eukarya. While the bacterial RPR is catalytically active in vitro, only select euryarchaeal and eukaryal RPRs are weakly active despite secondary structure similarity and conservation of nucleotide identity in their putative catalytic core. Such a decreased archaeal/eukaryal RPR function might imply that their cognate RPPs provide the functional groups that make up the active site. However, substrate-binding defects might mask the ability of some of these RPRs, such as that from the archaeon Methanocaldococcus jannaschii (Mja), to catalyze precursor tRNA (ptRNA) processing. To test this hypothesis, we constructed a ptRNA-Mja RPR conjugate and found that indeed it self-cleaves efficiently (kobs, 0.15 min−1 at pH 5.5 and 55°C). Moreover, one pair of Mja RPPs (POP5-RPP30) enhanced kobs for the RPR-catalyzed self-processing by ∼100-fold while the other pair (RPP21-RPP29) had no effect; both binary RPP complexes significantly reduced the monovalent and divalent ionic requirement. Our results suggest a common RNA-mediated catalytic mechanism in all RNase P and help uncover parallels in RNase P catalysis hidden by plurality in its subunit make-up.
doi:10.1093/nar/gkn360
PMCID: PMC2475606  PMID: 18558617
14.  Studies on the mechanism of inhibition of bacterial ribonuclease P by aminoglycoside derivatives 
Nucleic Acids Research  2007;36(2):697-704.
Ribonuclease P (RNase P) is a Mg2+-dependent endoribonuclease responsible for the 5′-maturation of transfer RNAs. It is a ribonucleoprotein complex containing an essential RNA and a varying number of protein subunits depending on the source: at least one, four and nine in Bacteria, Archaea and Eukarya, respectively. Since bacterial RNase P is required for viability and differs in structure/subunit composition from its eukaryal counterpart, it is a potential antibacterial target. To elucidate the basis for our previous finding that the hexa-arginine derivative of neomycin B is 500-fold more potent than neomycin B in inhibiting bacterial RNase P, we synthesized hexa-guanidinium and -lysyl conjugates of neomycin B and compared their inhibitory potential. Our studies indicate that side-chain length, flexibility and composition cumulatively account for the inhibitory potency of the aminoglycoside-arginine conjugates (AACs). We also demonstrate that AACs interfere with RNase P function by displacing Mg2+ ions. Moreover, our finding that an AAC can discriminate between a bacterial and archaeal (an experimental surrogate for eukaryal) RNase P holoenzyme lends promise to the design of aminoglycoside conjugates as selective inhibitors of bacterial RNase P, especially once the structural differences in RNase P from the three domains of life have been established.
doi:10.1093/nar/gkm1088
PMCID: PMC2241863  PMID: 18084035
15.  Elucidation of structure–function relationships in the protein subunit of bacterial RNase P using a genetic complementation approach 
Nucleic Acids Research  2002;30(23):5065-5073.
RNase P is a ribonucleoprotein involved in tRNA biosynthesis in all living organisms. Bacterial RNase P is comprised of a catalytic RNA subunit and a lone protein cofactor which plays a supporting, albeit essential, role in the tRNA processing reaction in vivo. In this study, we have searched various databases to identify homologs of the protein subunit of RNase P from diverse bacteria and used an alignment of their primary sequences to determine the most highly conserved residues, and thereby extend earlier predictions of which residues might play an important role in RNA recognition. By employing a genetic complementation assay, we have also gained insights into structure– function relationships in the protein subunit of bacterial RNase P.
PMCID: PMC137979  PMID: 12466529

Results 1-15 (15)