The amino acid sequence of iguana (Iguana iguana) pancreatic ribonuclease

Emerging biological functions of ribonuclease 1 and angiogenin

Pancreatic-type ribonucleases (ptRNases) are a large family of vertebrate-specific secretory endoribonucleases. These enzymes catalyze the degradation of many RNA substrates and thereby mediate a variety of biological functions. Though the homology of ptRNases has informed biochemical characterization and evolutionary analyses, the understanding of their biological roles is incomplete. Here, we review the functions of two ptRNases: RNase 1 and angiogenin. RNase 1, which is an abundant ptRNase with high catalytic activity, has newly discovered roles in inflammation and blood coagulation. Angiogenin, which promotes neovascularization, is now known to play roles in the progression of cancer and amyotrophic lateral sclerosis, as well as in the cellular stress response. Ongoing work is illuminating the biology of these and other ptRNases.

Leczyme: a new candidate drug for cancer therapy

Sialic acid-binding lectin (SBL), isolated from oocytes of Rana catesbeiana, is leczyme and has both lectin and ribonuclease (RNase) activities. A remarkable antitumor effect of SBL has also been reported. SBL agglutinates various kinds of tumor cells but not normal cells. SBL agglutination activity is not affected by mono- or oligosaccharides. However, SBL-induced agglutination and antitumor effects are inhibited by sialomucin but not asialomucin. In addition, SBL has very little effect on sialidase-treated cells. SBL causes cancer-selective induction of apoptosis by multiple signaling pathways, which target RNA. Synergistic antitumor effects with other molecules, such as tumor necrosis factor-related apoptosis ligand (TRAIL) and interferon-γ (IFN-γ), have been reported. Thus, SBL may be a novel candidate molecule for anticancer drug development. Sialoglycoconjugates on the tumor cell surface may be associated with lectin activity and antitumor effects of SBL. We review the properties of SBL, particularly its lectin, RNase, and antitumor activities, and comprehensively examine the potential application of SBL for clinical purposes.

Ribonucleases with angiogenic and bactericidal activities from the Atlantic salmon

The importance of fish in vertebrate evolution has been better recognized in recent years after the intense work carried out on fish genomics. The recent discovery that fish genomes comprise homologs of ribonucleases, studied before only in tetrapods, and the isolation of ribonucleases from zebrafish have suggested an experimental model for studying fish and vertebrate evolution. Thus, the cDNAs encoding the RNases from the Atlantic salmon were expressed, and the recombinant RNases (Ss-RNase-1 and Ss-RNase-2) were isolated and characterized as both proteins and for their biological activities. Salmon RNases are less active than RNase A in degrading RNA, but are both sensitive to the action of the human cytosolic RNase inhibitor. The two enzymes possess both angiogenic and bactericidal activities. However, catalytically inactivated Ss-RNases do not exert any angiogenic activity, but preserve their full bactericidal activity, which is surprisingly preserved even when the enzyme proteins are fully denatured. Analyses of the conformational stability of the two RNases has revealed that they are as stable as typical RNases of the superfamily, and Ss-RNase-2, the most active as an enzyme, is also the most resistant to thermal and chemical denaturation. The implications of these findings in terms of the evolution of early RNases, in particular of the physiological significance of the angiogenic and bactericidal activities of fish RNases, are analyzed and discussed.

Zebrafish Ribonucleases Are Bactericidal: Implications for the Origin of the Vertebrate RNase A Superfamily

Understanding the evolutionary origin of the ribonuclease (RNase) A superfamily is of great interest because the superfamily is the sole vertebrate-specific enzyme family known to date. Although mammalian RNases have a diverse array of biochemical and physiological functions, the original function of the superfamily at its birth is enigmatic. Such information may be obtained by studying basal lineages of the vertebrate phylogeny and is necessary for discerning how and why this superfamily originated. Here, we clone and characterize 3 RNase genes from the zebrafish, the most basal vertebrate examined for RNases. We report 1) that all the 3 zebrafish RNases are ribonucleolytically active, with one of them having an RNase activity comparable to that of bovine RNase A, the prototype of the superfamily; 2) that 2 zebrafish RNases have prominent expressions in adult liver and gut, whereas the 3rd is expressed in adult eye and heart; and 3) that all 3 RNases have antibacterial activities in vitro. These results, together with the presence of antibacterial and/or antiviral activities in multiple distantly related mammalian RNases, strongly suggest that the superfamily started as a host-defense mechanism in vertebrate evolution.

Enzymatic Properties of Newly Found Green Turtle Egg White Ribonuclease

Egg white ribonuclease was first found in green turtle eggs. The general properties were studied on substrate specificity, the optimum pH and temperature, and the effect of pH and temperature on the RNase activity. The enzyme studied was specific for poly (C) and degraded poly (U) at the lower rate and had the pH optimum at 7.0 and the optimum temperature at 40 degrees C. It was stable at alkaline range (pH 8.0-10.0) and up to 60 degrees C in pH 9.0 for 1 h, and unstable at acidic side for all temperatures. All of the properties studied showed similarity to RNase A. However, the optimum pH, broad range of optimum temperature and pH stability were different from RNase A. To evaluate the relationship of the structure and enzymatic properties, the 3D-structure of this enzyme was engineered by program MODELLER using two RNases (2BWL and 2BLZ) as starting models. The differences found in activity might be affected from the structure of micro environmental changing caused by amino acids deletion and substitution on the molecule.

The Complete Amino Acid Sequence of Green Turtle (Chelonia mydas) Egg White Ribonuclease

Egg white ribonuclease was first found in green turtle eggs. This enzyme has been purified by CM-toyopearl cation exchange. Two isoforms (GTRNase-1 and GTRNase-2) were further separated by RP-HPLC, with the same M.W. (13 kDa) and activity. These isoforms carried one amino acid exchange of Ser and Leu at the position 37. The N-terminal sequence, ETRYEKF, was determined for the transblotted protein. Internal sequences were analyzed by protein sequencer and ESI-Q-TOF mass spectrometry for tryptic peptides (Ts). The overlapping sequences were obtained from chymotryptic peptides, CNBr fragments and ISD-MS/MS analysis. The C-terminal Ile was identified by CPase-Y. The established sequence composed of 119 residues with the molecular mass of 12,942.1 Da for GTRNase-1 and 12,967.8 Da for GTRNase-2. The comparison of sequence with known pancreatic RNases, 27 positions including catalytic residues at the position 11 and 114 were conserved. Also basic residues contributed to phosphate binding residues were conserved with the exception of Lys 66. One insertion at the position 14, and 3 deletions at the position-1, between position 64-65, and 110 and 111 were found. Two Cys residues at position 65 and 72 that form a disulfide bond in mammalian RNase were deleted and exchanged. All these difference in the sequence were similar to reptile pancreatic RNase.

Evolution and Function of Leukocyte RNase A Ribonucleases of the Avian Species, Gallus gallus

In this study, we explore the evolution and function of two closely related RNase A ribonucleases from the chicken, Gallus gallus. Separated by approximately 10 kb on chromosome 6, the coding sequences of RNases A-1 and A-2 are diverging under positive selection pressure (dN > dS) but remain similar to one another (81% amino acid identity) and to the mammalian angiogenins. Immunoreactive RNases A-1 and A-2 (both approximately 16 kDa) were detected in peripheral blood granulocytes and bone marrow. Recombinant proteins are ribonucleolytically active (kcat = 2.6 and 0.056 s(-1), respectively), and surprisingly, both interact with human placental ribonuclease inhibitor. RNase A-2, the more cationic (pI 11.0), is both angiogenic and bactericidal; RNase A-1 (pI 10.2) has neither activity. We demonstrated via point mutation of the catalytic His110 that ablation of ribonuclease activity has no impact on the bactericidal activity of RNase A-2. We determined that the divergent domains II (amino acids 71-76) and III (amino acids 89-104) of RNase A-2 are both important for bactericidal activity. Furthermore, we demonstrated that these cationic domains can function as independent bactericidal peptides without the tertiary structure imposed by the RNase A backbone. These results suggest that ribonucleolytic activity may not be a crucial constraint limiting the ongoing evolution of this gene family and that the ribonuclease backbone may be merely serving as a scaffold to support the evolution of novel, nonribonucleolytic proteins.

Characterization of a ribonuclease gene and encoded protein from the reptile, Iguana iguana

In this work we identify an intronless open reading frame encoding an RNase A ribonuclease from genomic DNA from the Iguana iguana IgH2 cell line. The iguana RNase is expressed primarily in pancreas, and represents the majority of the specific enzymatic activity in this tissue. The encoded sequence shares many features with its better-known mammalian counterparts including the crucial His12, Lys40 and His114 catalytic residues and efficient hydrolytic activity against yeast tRNA substrate (k(cat)/K(m)=6 x 10(4) M(-1) s(-1)), albeit at a reduced pH optimum (pH 6.0). Although the catalytic activity of the iguana RNase is not diminished by human placental RI, iguana RNase is not bactericidal nor is it cytotoxic even at micromolar concentrations. Phylogenetic analysis indicates moderate (46%) amino acid sequence similarity to a pancreatic RNase isolated from Chelydra serpentina (snapping turtle) although no specific relationship could be determined between these RNases and the pancreatic ribonucleases characterized among mammalian species. Further analysis of ribonucleases from non-mammalian vertebrate species is needed in order to define relationships and lineages within the larger RNase A gene superfamily.

Secretory ribonucleases in the primitive ruminant chevrotain (Tragulus javanicus)

Phylogenetic analyses of secretory ribonucleases or RNases 1 have shown that gene duplication events, giving rise to three paralogous genes (pancreatic, seminal and brain RNase), occurred during the evolution of ancestral ruminants. A higher number of paralogous sequences are present in chevrotain (Tragulus javanicus), the earliest diverged taxon within the ruminants. Two pancreatic RNase sequences were identified, one encoding the pancreatic enzyme, the other encoding a pseudogene. The identity of the pancreatic enzyme was confirmed by isolation of the protein and N-terminal sequence analysis. It is the most acidic pancreatic ribonuclease identified so far. Formation of the mature enzyme requires cleavage by signal peptidase of a peptide bond between two glutamic acid residues. The seminal-type RNase gene shows features of a pseudogene, like orthologous genes in other ruminants investigated with the exception of the bovine species. The brain-type RNase gene of chevrotain is expressed in brain tissue. A hybrid gene with a pancreatic-type N-terminal and a brain-type C-terminal sequence has been identified but nothing is known about its expression. Phylogenetic analysis of RNase 1 sequences of six ruminant, three other artiodactyl and two whale species support previous findings that two gene duplications occurred in a ruminant ancestor. Three distinct groups of pancreatic, seminal-type and brain-type RNases have been identified and within each group the chevrotain sequence it the first to diverge. In taxa with duplications of the RNase gene (ruminants and camels) the gene evolved at twice as fast than in taxa in which only one gene could be demonstrated; in ruminants there was an approximately fourfold increase directly after the duplications and then a slowing in evolutionary rate.

Contribution of disulfide bonds to the conformational stability and catalytic activity of ribonuclease A

Disulfide bonds between the side chains of cysteine residues are the only common crosslinks in proteins. Bovine pancreatic ribonuclease A (RNase A) is a 124-residue enzyme that contains four interweaving disulfide bonds (Cys26-Cys84, Cys40-Cys95, Cys58-Cys110, and Cys65-Cys72) and catalyzes the cleavage of RNA. The contribution of each disulfide bond to the conformational stability and catalytic activity of RNase A has been determined by using variants in which each cystine is replaced independently with a pair of alanine residues. Thermal unfolding experiments monitored by ultraviolet spectroscopy and differential scanning calorimetry reveal that wild-type RNase A and each disulfide variant unfold in a two-state process and that each disulfide bond contributes substantially to conformational stability. The two terminal disulfide bonds in the amino-acid sequence (Cys26-Cys84 and Cys58-Cys110) enhance stability more than do the two embedded ones (Cys40-Cys95 and Cys65-Cys72). Removing either one of the terminal disulfide bonds liberates a similar number of residues and has a similar effect on conformational stability, decreasing the midpoint of the thermal transition by almost 40 degrees C. The disulfide variants catalyze the cleavage of poly(cytidylic acid) with values of kcat/Km that are 2- to 40-fold less than that of wild-type RNase A. The two embedded disulfide bonds, which are least important to conformational stability, are most important to catalytic activity. These embedded disulfide bonds likely contribute to the proper alignment of residues (such as Lys41 and Lys66) that are necessary for efficient catalysis of RNA cleavage.

An angiogenic protein from bovine serum and milk--purification and primary structure of angiogenin-2

Bovine serum and milk contain a basic angiogenic protein that binds tightly to placental ribonuclease inhibitor. It was purified from both sources by ion-exchange and reversed-phase chromatographies. Its amino acid sequence revealed that it is a member of the ribonuclease superfamily. It contains 123 amino acids in a single polypeptide chain, is cross-linked by three disulfide bonds, is glycosylated at Asn33, and is 57% identical to bovine angiogenin. The amino-terminal and carboxyl-terminal residues are pyroglutamic acid and proline, respectively. The protein has ribonucleolytic activity that is similar to, but somewhat lower than, that of bovine angiogenin, i.e. very low relative to RNase. It is angiogenically potent on chicken chorioallantoic membrane, but less so than angiogenin. The sequence and activities demonstrate that this protein is a second, distinct, member of the angiogenin sub-family of pancreatic ribonucleases, and is referred to as angiogenin-2.

Primary structures of two ribonucleases from ginseng calluses. New members of the PR-10 family of intracellular pathogenesis-related plant proteins

The amino acid sequences of two ribonucleases from a callus cell culture of Panax ginseng were determined. The two sequences differ at 26% of the amino acid positions. Homology was found with a large family of intracellular pathogenesis-related proteins, food allergens and tree pollen allergens from both dicotyledonous and monocotyledonous plant species. There is about 30% sequence difference with proteins from species belonging to the same plant order (Apiales: parsley and celery), 60% with those from four other dicotyledonous plant orders and about 70% from that of the monocotyledonous asparagus. More thorough evolutionary analyses of sequences lead to the conclusion that the general biological function of members of this protein family may be closely related to the ability to cleave intracellular RNA and that they have an important role in cell metabolism. As the three-dimensional structure of one of the members of this protein family has been determined recently [Gajhede et al., Nature Struct Biol 3 (1996) 1040-1045], it may be possible to assign active-site residues in the enzyme molecule and make hypotheses about its mode of action. Structural features in addition to the cellular site of biosynthesis indicate that this family of ribonucleases is very different from previously investigated ones.