Novel dipeptidyl peptidase IV resistant analogues of glucagon-like peptide-1(7-36)amide have preserved biological activities in vitro conferring improved glucose-lowering action in vivo

Although the incretin hormone glucagon-like peptide-1 (GLP-1) is a potent stimulator of insulin release, its rapid degradation in vivo by the enzyme dipeptidyl peptidase IV (DPP IV) greatly limits its potential for treatment of type 2 diabetes. Here, we report two novel Ala(8)-substituted analogues of GLP-1, (Abu(8))GLP-1 and (Val(8) GLP-1 which were completely resistant to inactivation by DPP IV or human plasma. (Abu(8))GLP-1 and (Val(8))GLP-1 exhibited moderate affinities (IC50: 4.76 and 81.1 nM, respectively) for the human GLP-1 receptor compared with native GLP-1 (IC50: 0.37 nM). (Abu(8))GLP-1 and (Val(8))GLP-1 dose-dependently stimulated cAMP in insulin-secreting BRIN BD11 cells with reduced potency compared with native GLP-1 (1.5- and 3.5-fold, respectively). Consistent with other mechanisms of action, the analogues showed similar, or in the case of (Val(8))GLP-1 slightly impaired insulin releasing activity in BRIN BD11 cells. Using adult obese (ob/ob) mice, (Abu(8))GLP-1 had similar glucose-lowering potency to native GLP-1 whereas the action of (Val(8))GLP-1 was enhanced by 37%. The in vivo insulin-releasing activities were similar. These data indicate that substitution of Ala(8) in GLP-1 with Abu or Val confers resistance to DPP IV inactivation and that (Val(8))GLP-1 is a particularly potent N-terminally modified GLP-1 analogue of possible use in type 2 diabetes.

Sediment distribution, hydrolytic enzyme profiles and bacterial activities in the guts of Oneirophanta mutabilis, Psychropotes longicauda and Pseudostichopus - what do they tell us about digestive strategies of abyssal holothurians?

This paper describes inter-specific differences in the distribution of sediment in the gut compartments and in the enzyme and bacterial profiles along the gut of abyssal holothurian species — Oneirophanta mutabilis, Psychropotes longicauda and Pseudostichopus villosus sampled from a eutrophic site in the NE Atlantic at different times of the year. Proportions of sediments, relative to total gut contents, in the pharynx, oesophagus, anterior and posterior intestine differed significantly in all the inter-species comparisons, but not between inter-seasonal comparisons. Significant differences were also found between the relative proportions of sediments in both the rectum and cloaca of Psychropotes longicauda and Oneirophanta mutabilis. Nineteen enzymes were identified in either gut-tissue or gut-content samples of the holothurians studied. Concentrations of the enzymes in gut tissues and their contents were highly correlated. Greater concentrations of the enzymes were found in the gut tissues suggesting that they are the main source of the enzymes. The suites of enzymes recorded were broadly similar in each of the species sampled collected regardless of the time of the year, and they were similar to those described previously for shallow-water holothurians. Significant inter-specific differences in the gut tissue concentrations of some of the glycosidases suggest dietary differences. For example, Psychropotes longicauda and Pseudostichopus villosus contain higher levels of chitobiase than Oneirophanta mutabilis. There were no seasonal changes in bacterial activity profiles along the guts of O. mutabilis and Pseudostichopus villosus. In both these species bacterial activity and abundance declined between the pharynx/oesophagus and anterior intestine, but then increased along the gut and became greatest in the rectum/cloaca. Although the data sets were more limited for Psychropotes longicauda, bacterial activity increased from the anterior to the posterior intestine but then declined slightly to the rectum/cloaca. These changes in bacterial activity and densities probably reflect changes in the microbial environment along the guts of abyssal holothurians. Such changes suggest that there is potential for microbial breakdown of a broader range of substrates than could be otherwise be achieved by the holothurian itself. However, the present study found no evidence for sedimentary (microbial) sources of hydrolytic enzymes.

Multiple Enzymatic Activities Associated with Severe Acute Respiratory Syndrome Coronavirus Helicase

Severe acute respiratory syndrome coronavirus (SARS-CoV), a newly identified group 2 coronavirus, is the causative agent of severe acute respiratory syndrome, a life-threatening form of pneumonia in humans. Coronavirus replication and transcription are highly specialized processes of cytoplasmic RNA synthesis that localize to virus-induced membrane structures and were recently proposed to involve a complex enzymatic machinery that, besides RNA-dependent RNA polymerase, helicase, and protease activities, also involves a series of RNA-processing enzymes that are not found in most other RNA virus families. Here, we characterized the enzymatic activities of a recombinant form of the SARS-CoV helicase (nonstructural protein [nsp] 13), a superfamily 1 helicase with an N-terminal zinc-binding domain. We report that nsp13 has both RNA and DNA duplex-unwinding activities. SARS-CoV nsp13 unwinds its substrates in a 5'-to-3' direction and features a remarkable processivity, allowing efficient strand separation of extended regions of double-stranded RNA and DNA. Characterization of the nsp13-associated (deoxy)nucleoside triphosphatase ([dNTPase) activities revealed that all natural nucleotides and deoxynucleotides are substrates of nsp13, with ATP, dATP, and GTP being hydrolyzed slightly more efficiently than other nucleotides. Furthermore, we established an RNA 5'-triphosphatase activity for the SARS-CoV nsp13 helicase which may be involved in the formation of the 5' cap structure of viral RNAs. The data suggest that the (d)NTPase and RNA 5'-triphosphatase activities of nsp13 have a common active site. Finally, we established that, in SARS-CoV-infected Vero E6 cells, nsp13 localizes to membranes that appear to be derived from the endoplasmic reticulum and are the likely site of SARS-CoV RNA synthesis.

Identification of protease and ADP-ribose 1''-monophosphatase activities associated with transmissible gastroenteritis virus non-structural protein 3.

The replicase polyproteins, pp1a and pp1ab, of porcine Transmissible gastroenteritis virus (TGEV) have been predicted to be cleaved by viral proteases into 16 non-structural proteins (nsp). Here, enzymic activities residing in the amino-proximal region of nsp3, the largest TGEV replicase processing product, were characterized. It was shown, by in vitro translation experiments and protein sequencing, that the papain-like protease 1, PL1pro, but not a mutant derivative containing a substitution of the presumed active-site nucleophile, Cys1093, cleaves the nsp2|nsp3 site at 879Gly|Gly880. By using an antiserum raised against the pp1a/pp1ab residues 526–713, the upstream processing product, nsp2, was identified as an 85 kDa protein in TGEV-infected cells. Furthermore, PL1pro was confirmed to be flanked at its C terminus by a domain (called X) that mediates ADP-ribose 1''-phosphatase activity. Expression and characterization of a range of bacterially expressed forms of this enzyme suggest that the active X domain comprises pp1a/pp1ab residues Asp1320–Ser1486.

Human coronavirus 229E nonstructural protein 13: characterization of duplex-unwinding, nucleoside triphosphatase, and RNA 5'-triphosphatase activities.

The human coronavirus 229E (HCoV-229E) replicase gene-encoded nonstructural protein 13 (nsp13) contains an N-terminal zinc-binding domain and a C-terminal superfamily 1 helicase domain. A histidine-tagged form of nsp13, which was expressed in insect cells and purified, is reported to unwind efficiently both partial-duplex RNA and DNA of up to several hundred base pairs. Characterization of the nsp13-associated nucleoside triphosphatase (NTPase) activities revealed that all natural ribonucleotides and nucleotides are substrates of nsp13, with ATP, dATP, and GTP being hydrolyzed most efficiently. Using the NTPase active site, HCoV-229E nsp13 also mediates RNA 5'-triphosphatase activity, which may be involved in the capping of viral RNAs.

A complex zinc finger controls the enzymatic activities of nidovirus helicases.

Nidoviruses (Coronaviridae, Arteriviridae, and Roniviridae) encode a nonstructural protein, called nsp10 in arteriviruses and nsp13 in coronaviruses, that is comprised of a C-terminal superfamily 1 helicase domain and an N-terminal, putative zinc-binding domain (ZBD). Previously, mutations in the equine arteritis virus (EAV) nsp10 ZBD were shown to block arterivirus reproduction by disrupting RNA synthesis and possibly virion biogenesis. Here, we characterized the ATPase and helicase activities of bacterially expressed mutant forms of nsp10 and its human coronavirus 229E ortholog, nsp13, and correlated these in vitro activities with specific virus phenotypes. Replacement of conserved Cys or His residues with Ala proved to be more deleterious than Cys-for-His or His-for-Cys replacements. Furthermore, denaturation-renaturation experiments revealed that, during protein refolding, Zn2+ is essential for the rescue of the enzymatic activities of nidovirus helicases. Taken together, the data strongly support the zinc-binding function of the N-terminal domain of nidovirus helicases. nsp10 ATPase/helicase deficiency resulting from single-residue substitutions in the ZBD or deletion of the entire domain could not be complemented in trans by wild-type ZBD, suggesting a critical function of the ZBD in cis. Consistently, no viral RNA synthesis was detected after transfection of EAV full-length RNAs encoding ATPase/helicase-deficient nsp10 into susceptible cells. In contrast, diverse phenotypes were observed for mutants with enzymatically active nsp10, which in a number of cases correlated with the activities measured in vitro. Collectively, our data suggest that the ZBD is critically involved in nidovirus replication and transcription by modulating the enzymatic activities of the helicase domain and other, yet unknown, mechanisms.

The human coronavirus 229E superfamily 1 helicase has RNA and DNA duplex-unwinding activities with 5'-to-3' polarity.

The human coronavirus 229E replicase gene encodes a protein, p66HEL, that contains a putative zinc finger structure linked to a putative superfamily (SF) 1 helicase. A histidine-tagged form of this protein, HEL, was expressed using baculovirus vectors in insect cells. The purified recombinant protein had in vitro ATPase activity that was strongly stimulated by poly(U), poly(dT), poly(C), and poly(dA), but not by poly(G). The recombinant protein also had both RNA and DNA duplex-unwinding activities with 5'-to-3' polarity. The DNA helicase activity of the enzyme preferentially unwound 5'-oligopyrimidine-tailed, partial-duplex substrates and required a tail length of at least 10 nucleotides for effective unwinding. The combined data suggest that the coronaviral SF1 helicase functionally differs from the previously characterized RNA virus SF2 helicases.