In vitro disulfide-coupled folding of guanylyl cyclase-activating peptide and its precursor protein

Guanylyl cyclase-activating peptide II (GCAP-II), an endogenous ligand of particulate guanylyl cyclase C (GC-C), is processed from the precursor protein and circulates in human blood. GCAP-II consists of 24 amino acid residues and contains two disulfide bridges. The correct disulfide paring of GCAP-II is an absolute requirement for its biological activity. This study shows that the folding of the peptide from the reduced form yields a peptide with the native disulfide paring as a minor product and with non-native ones as major products, regardless of the presence or absence of reduced and oxidized glutathione. The results suggest that GCAP-II does not possess sufficient information to permit the adoption of the native conformation and to effectively form the correct disulfide pairing and, as a result, that GCAP-II is correctly folded by assistance of a factor(s) such as an intra- or intermolecular chaperone. We studied whether a peptide in the pro-leader sequence of the precursor protein (proGCAP-II) contains sufficient information to facilitate the folding of GCAP-II. For this purpose, we prepared proGCAP-II in Escherichia coli by a recombinant technique and examined the disulfide-coupled folding of proGCAP-II from the reduced form. proGCAP-II was quantitatively recovered with the correctly folded structure from the reduced form both in the presence and in the absence of reduced and oxidized glutathione. The protein contains only disulfide linkages at the same positions as the mature form of proGCAP-II, GCAP-II, and the biologically active isomer of GCAP-II in the molecule. These results provide evidence that the propeptide of proGCAP-II is a critical factor in the formation of the correct disulfide paring in the folding of the protein.

Uroguanylin: gene structure, expression, processing as a peptide hormone, and co-storage with somatostatin in gastrointestinal D-cells

Guanylin/GCAP-I and uroguanylin/GCAP-II are two structurally related peptides which play an important role in the regulation of water/electrolyte balance within the gut. In order to enable the investigation and comparison of both peptide hormones at the genomic level, we decided to clone the corresponding genes. The human gene for guanylin/GCAP-I and its 5'-flanking region have been described recently. Here, we report the three exon/two intron structure of the human uroguanylin/GCAP-II gene and its localization on chromosome 1 p35-34, as determined by radiation hybrid mapping. Together with data obtained for the guanylin/GCAP-I gene we show that these genes are localized in the same chromosomal area with other guanlyl cyclase-activating peptides like ANP etc. Northern hybridization revealed that the expression of the uroguanylin/GCAP-II gene is highest in the intestinal mucosa, especially in the ileum and colon. By means of polymerase chain reaction (PCR), an expression was also observed in the stomach where no guanylin/GCAP-I expression is detectable. Using immunohistochemical methods, uroguanylin/GCAP-II immunoreactive material was distinctly localized in D-type gastric and intestinal endocrine cells. Although the comparable data on the genomic organisation of both peptide hormones verify their high degree of relationship, this finding indicates a special task of uroguanylin/GCAP-II within the stomach, such as regulatory functions in gastric secretion. The redundant expression of the GCAP/GC-C system in the small and large intestine, however, is as yet unclear.

New technologies for amperometric biosensors

Amperomeric-based detectors have successfully been used as personal monitors for blood glucose levels. However, there is a desire to increase the number of compounds measured in a small blood sample, the speed of detection and enhance the reliability of the measurement. Furthermore, with the increasing use of microdialysis as a clinical sampling method in metabolic medicine, paediatric medicine and neurointensive care, there is a need for rapid on-line detection of analytes such as lactate, glucose and glutamate in low microlitre volume samples. Two approaches to these problems are described. The first uses enzymes immobilized in a packed bed with electrochemical detection of a ferrocene mediator as a flow-injection assay for use with microdialysis. Results from microdialysis of the brain of freely moving rats are described. In the second approach, thin-film techniques are used to fabricate arrays of microdisk and micro line electrodes. The properties of these arrays in free solution and in a flow cell are presented together with an example using multiple arrays to identify an analyte by oxidation potential. Finally, different enzymes are entrapped onto the surface of two arrays by electrochemical polymerization of o-phenylenediamine. The resulting device detects glucose and lactate in real-time.

Functional analysis of the human guanylin gene promoter

Guanylin (GCAP-I, guanylate cyclase activating peptide I) and uroguanylin (GCAP-II, guanylate cyclase activating peptide II) are regulatory peptides involved in the regulation of the intestinal chloride / water balance. They share significant structural homology to the E. coli enterotoxin STa, which binds to the particulate guanylyl cyclase C causing diarrhea in mammals. In this study we report the functional analysis of the guanylin / GCAP-I gene promoter region. By means of the luciferase reporter gene assay, we demonstrate a strong promoter activity in T84 cells. Especially the first 160 bp of the 5'-flanking region of the gene seem to be essential for gene induction. Our findings are the basis for further identification of important regulatory elements of the corresponding gene.

A new human guanylate cyclase-activating peptide (GCAP-II, uroguanylin): precursor cDNA and colonic expression

We have amplified, cloned, and sequenced 583 bp GCAP-II/uroguanylin-specific cDNA from human colon cDNA first strand. The cDNA codes for a putative 112 amino-acid precursor protein including the sequence of uroguanylin and GCAP-II. Northern blot hybridization revealed a high level expression of the GCAP-II gene in human colon, but not in the kidney. This expression of GCAP-II indicates a pivotal role in cGMP-mediated functions of the colon.

Analysis of the human guanylin gene and the processing and cellular localization of the peptide

The complete cell biological analysis of human guanylin, a recently discovered regulatory peptide, is offered in this investigation: (i) the nucleotide sequence of the gene, (ii) the isolation and characterization of its circulating molecular form, and (iii) its localization in enterochromaffin cells of the gut. As determined by molecular cloning, DNA sequencing, and comparison with the known cDNA sequence, the approximately 2.6-kbp large gene consists of three exons interrupted by two introns. The putative promoter region contains a TTTAAAA sequence motif and several potential binding sites for transcription factors such as AP-1, AP-2, Sp 1, and glucocorticoid receptors. The isolated hormonal form of guanylin is a 94-amino acid peptide with a molecular mass of 10.3 kDa. Western blot analysis of RP-HPLC fractions from blood plasma confirms this molecular form. Thus, guanylin is synthesized by gut enterochromaffin cells as a prohormone of 115 amino acids and is processed to the molecular form of 94 amino acids circulating in the blood.

Reactions of electron-transfer proteins at electrodes

Studies of electron-transfer reactions of redox proteins have, in recent years, attracted widespread interest and attention. Progress has been evident from both physical and biological standpoints, with the increasing availability of three-dimensional structural data for many small electron-transfer proteins prompting a variety of systematic investigations (Isied, 1985). Most recently, attention has been directed towards questions concerning the elementary transfer of electrons between spatially remote redox sites, and the nature of protein–protein interactions which, for intermolecular processes, stabilize specific precursor complexes which may be optimally juxtaposed for electron-transfer. These and other issues, including the necessary reversibility of protein interfacial interactions and the dynamic properties of proteins as carriers of electrons in biological electron-transport systems, are now being addressed in the rapidly emerging field of direct (unmediated) protein electrochemistry. It is our intention in this article to discuss developments made in this area and highlight points which we believe to have the most bearing on our current understanding of diffusion-dominated, protein-mediated electron transport at electrode surfaces. First we shall outline some basic considerations which are best considered with reference to homogeneous systems.

Cell surface lipids and adhesion. IV. The effects of trypsin on lipid turnover by the plasmalemma

Trypsin treatment of intact cells or isolated plasmalemmae from embryonic chick neural retinae leads to an accumulation of lysophospholipids in the plasmalemmae. Trypsin was used at activities commonly used in cell disaggregation techniques. This accumulation appears to result from the decrease in acyltransferase activity in the plasmalemma produced by enzyme treatment. Plasmalemmal CoA ligase activity is not affected by trypsin treatment. Trypsinization has little effect on plasmalemmal phospholipase A2 activity. These results are discussed in relation to (a) the effects of trypsinization on cell adhesion, and (b) the theory that cells cannot adhere to lecithins because of their fluidity or surface-free-energy values. We propose that the effects of trypsinization on adhesion may in large part be due to the effects on other plasmalemmal proteins. Similarly the inability of cells to adhere to lecithin substrates is simply explained as being due to the lysolecithin that contacting cells release from these substrates.

Treatment of the fractured edentulous mandible

Fifty-three cases of fractures of edentulous mandibles were reviewed and analyzed. Thirty-three cases were sufficiently documented to assess the entire treatment course. Two nonunions were identified. Major factors contributing to the difficulty of repair of fractures include the location of the fracture, the height of the horizontal ramus, and the patient's systemic condition. Closed reduction of fractures of atrophic mandibular bodies is advocated. Although anatomical alignment may not be achieved by this approach, it may preclude nonunion and a prolonged clinical course.